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The dash number is a grade, ten being the highest. Probably relates to tolerances? Anyway, the power handling is separate.

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'66 911 #304065 Irischgruen
'81 R65
Ex-'71 911 PCA C-Stock Club Racer #806 (Sold 5/15/13)
Ex-'88 Carrera (Sold 3/29/02)
Ex-'91 Carrera 2 Cabriolet (Sold 8/20/04)
Ex-'89 944 Turbo S (Sold 8/21/20)
Old 06-25-2008, 07:23 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #21 (permalink)
Max Sluiter
 
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I replaced the transistors today. They were all (quantity 5) broken.

I tried the RPM drop test from 2000RPM to 1300RPM but there was no RPM variation when manually actuating the microswitch. I thought that the car may be in the warm-up mode so I took it out for a short drive to get it upt to 180F or close to it. I repeated the RPM drop test and there was no RPM variation.

I do not have a heater or thermostat but have a screw in its place. Do I need to turn the screw in to get the motor out of the warm-up setting and seeing the RPM transducer and microswitch?

I have checked that the microswitch is working electrically and mechanically.

Now I will test the inputs to the RPM transducer (14V power, ground, distributor) and if those are all good, I will shoot a square wave into it and see how the output Hertz look.

I noticed that 1500 RPM divided by the 75Hz output = 20 and 1300 RPM divided by the 65Hz output = 20.

For T1,T2,T3 and D1 I used a 2N2222A transistor. For T4, I used a 2N2102 transistor.

I am thinking that a Zener diode may be the better replacement for the D1transistor. The base of D1 is soldered to the board but does not have any elecrical connection, correct?

Any thoughts and suggestions are welcomed.
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911S
1971 chassis, 2.7RS spec MFI engine, suspension mods, lightened

Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance
http://www.flickr.com/photos/max_911_fahrer/
Old 06-27-2008, 07:40 PM
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Max -

The RPM Transducer doesn't care about engine temp - it works just fine cold. Other than the pleasure of driving the car it won't make any difference in troubleshooting the transducer.

Can't help with the electrical stuff, sorry. It's all mirrors and magic to me.

Jim
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Old 06-27-2008, 08:15 PM
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Well, I will have to check the inputs

I want this to work
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911S
1971 chassis, 2.7RS spec MFI engine, suspension mods, lightened

Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance
http://www.flickr.com/photos/max_911_fahrer/
Old 06-27-2008, 08:30 PM
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I tested the inputs and they all appear to be in order. The RPM Transducer still fails the RPM drop test.

I tested the microswitch again and it is open when I am actuating the throttle. It is closed when the throttle arm hits the switch. I appear to have a connection between the distributor and 3 of the connectors to the RPM relay. I have power and a ground to the RPM relay. It appears that the RPM transducer is connected properly to the microswitch circuit.

I am going to test that I have a signal to the shut-off solonoid when the microswitch is jumpered and that the solonoid is actuating when given the proper signal. When it gets 12 volts, it should push out the rod that contacts the injection pump main rack, correct? I have a spare pump and solonoid to confirm that the circuit is working if my solonoid should prove faulty or hard to diagnose.

Any tips on proceeding from here?

If I cannot get the system to work after testing the solonoid circuit, I will pull the RPM transducer and bench test it. I need to replicate the square wave from the disributor with my signal generator and then confirm that I have 8.2 Volts across the R5- R6 pathway. I may need to tune the R5 and R6 values as Warren says. I have my Zener diodes coming still on backorder.
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911S
1971 chassis, 2.7RS spec MFI engine, suspension mods, lightened

Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance
http://www.flickr.com/photos/max_911_fahrer/
Old 06-28-2008, 07:55 PM
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Max Sluiter
 
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I am testing the RPM Transducer out of the car on the bench because the solonoid works when jumpered but not when the speed switch is connected.

What does the input from the distributor points look like as far as wave form and amplitude? Wave form meaning sine wave, square wave, ramp... so that I know how to set my signal generator.

Where does the wire carrying the signal from the distributor points come off of the distributor? What color is the wire? I see that there are 2 wires coming out of the distributor case near the rotor and 1 goes into the wiring harness. I would like to "buzz" out the connection from the distributor to pin 4 on the transducer connector to make sure I have an input to the transducer.
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911S
1971 chassis, 2.7RS spec MFI engine, suspension mods, lightened

Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance
http://www.flickr.com/photos/max_911_fahrer/
Old 06-29-2008, 05:56 PM
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Flieger,

The signal should be an 11 volt square wave with a 63% duty cycle (that's 63% MARK, 37% space). Here's how I calculate that: 38 degrees of "DWELL" this is points CLOSED or MARK time followed by points opening then 22 degrees of SPACE time while the distributor cam holds them open. 38+22= 60 times 6 ignition events =360 degrees of distributor rotation. 38 degrees out of 60 per degrees per ignition events is 63%. Of course the CDI doesn't care about this, it fires on the falling edge. (At least I think it triggers on the falling edge, I have to check Warren's documentation for the answer).

How do we know it's 11 volts? Well, there's a 33 ohm pullup resistor inside the Bosch CDI, when the points are open, this resisistor pulls the input line up to bus voltage. When the points close the line gets pulled down to ground and the resistor limits the current that can flow to 420 mA (assuming 14V power to the CDI, internal bus voltage may be different?)

Actually, we know it's 11 volts because that's what the later tachs need to function according to an old email from VDO. If you have a tach up to 10/70, you probably have the silver can "intermediate unit" that is a step-up transformer to drive the tach off the ignition system.

On the diagnosis, connect +12v to one of the terminals of the microswitch, and a jumper from the other to the solenoid. The ground should be supplied by the bolts to the engine. That could be your problem.

The output from the speed switch should look like this:

Above 1500 (75hz input) - power OFF
1500-1300 (75-65hz input)- power ON
below 1300 (65 or lower, like when nothing is connected to the input line sitting on the bench)- power OFF

There are 2 wires off the distributor, one for the CDI, one for the tach. But there is only one connector. The tach wire should be black/purple whereas the CDI trigger is plain black.
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'66 911 #304065 Irischgruen
'81 R65
Ex-'71 911 PCA C-Stock Club Racer #806 (Sold 5/15/13)
Ex-'88 Carrera (Sold 3/29/02)
Ex-'91 Carrera 2 Cabriolet (Sold 8/20/04)
Ex-'89 944 Turbo S (Sold 8/21/20)

Last edited by 304065; 06-30-2008 at 07:17 AM..
Old 06-30-2008, 07:10 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #27 (permalink)
Max Sluiter
 
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Thanks for the info.

I think I will try to run a long jumper wire from the distributor to get the actual input into the RPM Transducer. My signal generator is old and I can't get it to go over 10 Volts but I am reading the manual to get the signal you mention.

I already jumpered the solonoid and I will test operation when running 12V from the connector of the Speed Switch output (pole 1) to the solonoid. The ground is good.

I think the problem is in the RPM Transducer. I have a regulated buss Voltage of 8.04 so I will need to tune the resistor values. I am still waiting on the 8.2 Volt Zener diode.

I appreciate your help.

Regards,

Max
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911S
1971 chassis, 2.7RS spec MFI engine, suspension mods, lightened

Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance
http://www.flickr.com/photos/max_911_fahrer/

Last edited by Flieger; 06-30-2008 at 05:13 PM..
Old 06-30-2008, 04:37 PM
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Max,

My advice would be to get a good signal going, then see what frequencies click the relay on and off, THEN consider changing the resistors.

Here's what I think is happening: when an input pulse is received at the base of T1, it saturates (it's an NPN unlike the Tach) and the T1's collector gets pulled to ground, turning T2 OFF and causing C4 to begin charging through R5 and R6. The RC time constant and the bus voltage determine how long this takes. Eventually C4 becomes fully charged and the right end is positive enough to turn T2 ON, pulling its collector to ground and turning T1 OFF. This establishes the pulse width for the first half of the circuit.

Anyway, I would work on getting a good pulse first so you can see which way the resistors need to move, if at all.
__________________
'66 911 #304065 Irischgruen
'81 R65
Ex-'71 911 PCA C-Stock Club Racer #806 (Sold 5/15/13)
Ex-'88 Carrera (Sold 3/29/02)
Ex-'91 Carrera 2 Cabriolet (Sold 8/20/04)
Ex-'89 944 Turbo S (Sold 8/21/20)
Old 07-01-2008, 05:56 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #29 (permalink)
Max Sluiter
 
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Thanks,

I will do some more checking on the weekend to investigate some incorrect component signal values.
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911S
1971 chassis, 2.7RS spec MFI engine, suspension mods, lightened

Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance
http://www.flickr.com/photos/max_911_fahrer/
Old 07-01-2008, 04:26 PM
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I thought more about a 555-based pulse generator-- configured for astable operation

the resistor relationships establish the duty cycle
the capacitor sets the frequency

for 63% duty cycle you want a 7/10 ratio, 7K ohms for R1 and 10K ohms for R2, and the cap varies, 0.80uf for 65Hz, 0.68uf for 76Hz (pretty close to 75)

You would need a single transistor output stage- an NPN with the base connected through a resistor to the 555's output pin 3, the emitter to ground and the collector to the tach input, a 33 ohm pullup resistor and then to the +14v power supply (also to pin 7 of the 555). I'll breadboard this and see if it works.
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'66 911 #304065 Irischgruen
'81 R65
Ex-'71 911 PCA C-Stock Club Racer #806 (Sold 5/15/13)
Ex-'88 Carrera (Sold 3/29/02)
Ex-'91 Carrera 2 Cabriolet (Sold 8/20/04)
Ex-'89 944 Turbo S (Sold 8/21/20)
Old 07-03-2008, 11:01 AM
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Here is a tacho generator in SPICE--- uses a 555 timer running in astable mode to generate a square wave from ground to about 11V.



--- Bill of Materials ---

Ref. Mfg. Part No. Description
C1 -- -- capacitor, 10mF
C2 -- -- capacitor, 680nF
Q1 -- NPN bipolar transistor
R1 -- -- resistor, 7K
R2 -- -- resistor, 10K
R3 -- -- resistor, 50
R4 -- -- resistor, 33
U1 Linear Technology NE555 integrated circuit
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'66 911 #304065 Irischgruen
'81 R65
Ex-'71 911 PCA C-Stock Club Racer #806 (Sold 5/15/13)
Ex-'88 Carrera (Sold 3/29/02)
Ex-'91 Carrera 2 Cabriolet (Sold 8/20/04)
Ex-'89 944 Turbo S (Sold 8/21/20)
Old 07-08-2008, 12:33 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #32 (permalink)
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Here is a simple output stage to transform a sine wave from a pulse generator that swings above and below ground into an 11 volt square wave. You have to adjust the pulse width to get the duty cycle right, but that's not hard.

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'66 911 #304065 Irischgruen
'81 R65
Ex-'71 911 PCA C-Stock Club Racer #806 (Sold 5/15/13)
Ex-'88 Carrera (Sold 3/29/02)
Ex-'91 Carrera 2 Cabriolet (Sold 8/20/04)
Ex-'89 944 Turbo S (Sold 8/21/20)
Old 07-08-2008, 02:59 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #33 (permalink)
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Update:

I put in my newly acquired Zener diode as a replacement for the D1 " transistor." I then scoped out the board but still found some odd voltage levels . Collector of T4 was stuck "high". I then removed C6 capacitor (10 micro-farads) and put in a suitable 10V square wave to replicate a distributor signal for the 1500 RPM range. The relay would chatter rapidly between ~55 Hz and ~73 Hz, but only after removing C6. That was it for the day.

Next project was to tackle the discontinuity in the microswitch circuit. The solenoid worked when 12 v was applied. The microswitch buzzed out correctly, i.e it was electrically functioning, ON/OFF, but there was no signal coming through to the microswitch when 12 v was applied to pin 1 of the RPM Transducer's mating connector on the cars wiring harness. I found several broken and clipped wires, lots of electrical tape, and general kludged wiring. This car had a long, hard transformation from a 1971 911S to an RS 2.7 liter motor. Pin 8 on the connector at the back of the engine bay electrical panel was vacant. This is the pin that had a connection to the microswitch. I moved an unused pin over to #8 position and then reattached the broken crimp to the RPM transducer's output pin. I then cleaned up the wiring, shirnk-sleeving and tying back the wires and fixing broken insulation and weak points. I now had continuity.

Next I put the board back in and fired it up. It worked! I held the engine at 2000 RPM and my dad actuated the microswitch by hand. It hunted around between 1800 and 1300 or so and I could not hold it in that range with the throttle but at least something was happening.

We then both though of all the adjustment we had done to the screw that clicks the microswitch before we knew our circuit was cut and our RPM transducer was missing

I backed off the adjustment screw so that the microswitch was open until my foot was completely off the throttle. I made it so that if I roll off gently while puttering around town, it will stick open and run smoother. If I snap off the throttle at higher RPMs and speeds, it clicks shut.

That solved the issue. I can drive sensibly around town without the big blast of flame. I can hold the revs between 1000 RPM idle and 2000 for checking oil pressure, etc.

And, best of all, the engine is much more responsive to the throttle. There is more engine braking and less backfiring. It is saving gas and running smoother.

There are still a few smaller "tick" noises after engine braking, just transitioning back onto the throttle, but no more "BANG!" explosions of raw fuel. The "ticks" sound like a lean condition out of the exhaust. Maybe rusty heat exchangers?

I am going to think more about C6 capacitor, probably replacing it with a smaller capacitance value since the 10 UF value of C6 seems to be shunting the drive signal of the base of T3 to ground. I do not think the relay chatters in the car, only clicks open or closed at the extremes of the hunting range. The response time to dampen the occilations seems just adequate. But I also may take another shot at adjusting the R5 and R6 values on the bench.

So, my dad and I have rebuilt our whole Speed Switch fuel cutoff system. It shuts off on the over-run and provides smooth engine braking. We learned a lot, had fun and saved a lot of money. Thanks to all who helped, particularly David Reynolds for his RPM transducer core and also thanks to the late Early S Man for his work with the schematic and components. I will give it a more thorough road test this weekend and report the outcome.

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911S
1971 chassis, 2.7RS spec MFI engine, suspension mods, lightened

Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance
http://www.flickr.com/photos/max_911_fahrer/

Last edited by Flieger; 07-10-2008 at 08:10 PM..
Old 07-10-2008, 07:48 PM
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The driving this weekend was great. The car has a much crisper throttle response and engine note. It is much smoother and smells leaner.

On Saturday, the idle was rising up into the range where the RPM transducer took effect, which caused annoying hunting until the engine was fully warmed up. On Sunday, I put the 114 mm MFI injection pump throttle rod back into spec. It was about 119 mm. This made the car idle higher and rougher, still hunting, so I backed off the throttle bodies to lessen the idle air flow. This brought the idle down into the 1000 RPM range and stopped the hunting. It idles cleanly now, with no smoke, hunting, or excessive fuel smell. The air/fuel mixture seems much improved.

The throttle body air and MFI injection pump fuel adjustments seemed to make a big difference in drivability. The car is smooth and has a crisp, clean engine note to accompany the greater engine braking and better throttle response.

Now I will try to figure out how to hook up C6 capacitor so that I ca improve the function of the RPM transducer board. I may put a much smaller value of capacitor in its place. I am also going to try to tune the resistor R5 and R6 values so as to smooth out the small fluctuations at idle of about 100 RPM and to try to control the RPM range for fuel cutoff.
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911S
1971 chassis, 2.7RS spec MFI engine, suspension mods, lightened

Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance
http://www.flickr.com/photos/max_911_fahrer/

Last edited by Flieger; 07-13-2008 at 03:49 PM..
Old 07-13-2008, 03:43 PM
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Max Sluiter
 
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I measured the value of R5 and R6. They were 4250 Ohms and 620 Ohms respectively.

Output at pin 1 was 12V above 53 Hz with a 10V DC square wave input (my signal generator would not go higher). I used a 13V power supply to the RPM transducer. The K1 relay was "on" above 78 Hz and "off" at 53 Hz. Between these inputs, the relay chattered.

I used a potentiometer of 5000 Ohms to tune R5 and came up with a value of 3450 Ohms that had a good 12V output Hz range.

At 65 Hz, K1 was "off"- zero volts out at pin 1 of the board. Above 65 Hz, the relay chatters. At 83 Hz, it is "on" with 12V solid output. I got a 1000 Ohm resistor for R6 and a 3300 Ohm resistor for R5. I replaced the factory components with these new values and the output signal responded with a 65 Hz shutoff as it had with the potentiometer.

I found that the Hz output from the distributor corresponds to the RPM that the engine turns at if the Hz is multiplied by 20. ---> 75 Hz x 20 = 1500; 65 Hz x 20 = 1300; 55 Hz x 20 = 1100.

1100 was where my car was hunting at warm idle. It now runs smoothly with an idle circuit reactivation at 1300 RPM and an idle engine speed of 1100 warm. It runs smothly and cleanly at this speed. If I lower it, the engine feels rough and will not start without much effort and coaxing to life.

So, decrease the resistor values to move the bottom RPM cutoff up. Freq in Hz x 20 = RPM

Hope this can help someone.
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911S
1971 chassis, 2.7RS spec MFI engine, suspension mods, lightened

Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance
http://www.flickr.com/photos/max_911_fahrer/

Last edited by Flieger; 07-20-2008 at 07:59 PM..
Old 07-20-2008, 04:21 PM
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I just replaced T1, T2, D1, D3 and D4 on my speed switch. The anti-vibration gunk had trapped something corrosive against the wires of D3 and D4 - both were broken but held in place by chocolate. The others were loose in the case. I would have never seen the problem with D3/4 if I hadn't removed the gunk with a dental pick and noticed the wires move. Be sure to clean that stuff off so you can inspect all the components.

According to Warren's note, I replaced D1 with a 8.2v 1 watt zener rather than a 2n2222a.

Now, I will have to test the voltages on R5 and R6 while it's on the car. I don't have any other way to create the signals needed. Can I expect a drastically different voltage at R5 and R6 or will the zenner get things fairly close to 8.4v?

Meanwhile, someone mentioned the idea of using potentiometers at R5 and R6. Can anyone wade in on that idea?

Last edited by tharbert; 03-20-2009 at 11:59 AM..
Old 03-20-2009, 11:46 AM
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You can try what my Dad and I did. We soldered in a 10k ohm potentiometer for R5 and a 5k pot for R6. We were able to fine-tune the resistor values for the RPM settings high and low that we wanted. We then went and got normal resistors to run with.

We used an 8.2 volt Zener diode in place of the transistor in D1 position. The resistor values we ended up with were 3.3k ohm in R5 and 1k ohm in R6.

We also took capacitor C6 out of the circuit- the whole relay circuit worked properly only when C6 was out.

Your values will likely vary due to tolerance build-up. These component values were individually tuned for the correct rpm signal operation at the Bosch factory, as you know from Warren's notes.

We have a signal generator for the 12V DC offset square wave input used to replicate the tachometer signal and a bench power supply for the main power 12V like from the battery. Since you do not have these items, you could try the potentiometers or our approximate resistor values and see how the car runs, then go from there to find the proper R values.

Good luck. I hope this helps.

Cheers
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911S
1971 chassis, 2.7RS spec MFI engine, suspension mods, lightened

Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance
http://www.flickr.com/photos/max_911_fahrer/
Old 03-20-2009, 09:13 PM
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John, If you have a PC with a soundcard, you have an oscilloscope. Here.
Much cheaper than a real one (as in free), and that may help for your troubleshooting.
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Old 03-21-2009, 03:40 PM
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Hello Folks,
is the speed switch also creating the rpm speed signal?

The rpm speed signal ends in pin 43 black purple on the schematic. Is is
connected to the Pin 4 of the RPM transducer which is the Pin 1 of the points.
If i connect the pin 1 othe points directly to pin 43 rpm meter it won´t work.
If I put a funtction generator triggerpulse square 10V to the rpm meter it works as well.

Pin 4 on the RPM transducer is also Black/ Purple which is Pin 1 on the dizzy.
The signal on pin 1 is not a TTL signal it is more the a pulse.
The rpm meter does not like this pulse shape so it must be converted.

Is the signal conditioning also done by the speed switch?

My rpm meter is a 1972 unit.

BR bob




Old 06-07-2009, 02:54 AM
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