Engine compartment electrical question 2, 74

moneymanager · 10-27-2007, 03:59 PM

Well just yesterday I asked an electrical question and Warren Hall gave me the answer in less time than it took me to ask the question. I've put a 74 2.7 in a 73.5 and am sorting out the rear compartment electrics. Have made a lot of progress but several "loose ends" remain.
Can someone tell me what this is? I think it may be what Haynes calls an rpm sensor I think, and PET seems to call it a ballast resistor. It has two leads soldered in place and I believe was mounted on the aluminum elec panel in the rear compartment, about 5" rearward of the CD unit, but am not sure. Mine was kind of lying in the back of the car, seemingly unconnected. Where do the electric leads go?

Here's another pic of the rear-most part of that rear auxiliary electrical panel. At the lower right is a 6 pin connector (3 shovel connectors in one row, 3 below these.) Anyone know what this is?
Finally there's the five pin relay socket.
One pin of this socket is assoc'd w/alternator & CD box pin B.
Another pin goes to an unused multiconnector pin, apparently for an option.
Another pin goes to D- on voltage regulator.
Another pin goes to a key switched circuit from that goes to starter solenoid.
THis isn't the relay for the rear window heater which can't be seen on the panel. But what is it? I thought it might be related to the WUR but, if it is, why did the car run fine without the relay itself in place?
With this info in hand, I should be able to make another leap forward. Thanks for any help,

304065 · 04:40 PM

JH,

That's actually a capacitor. Porsche used them as noise filters for the ignition. (Ballast resistors were only used 64-68 and they were a square box, and the "intermediate unit" was used only in 69-70 and has three terminals.)

Second pic, I don't see a six pin connector. I see a pair of 14-pin connectors, a fuse box, three factory 1/4" fastons, pair of three-pin plugs and a relay socket.

The relay socket is for the warm-up regulator relay.

moneymanager · 10-27-2007, 05:06 PM

Hi John,
A capacitor? Any idea where it might be wired in, or what it would be called on the
schematic?
The six pin connector is the square unit just right of the relay socket. It looks like an integral part of the harness, not an add on. Your mention of the thermotime switch got me to take another look at it. Actually only four of the shovel pins in this six pin connector are activated. One has two brown grounds, another pin gets two reds, the third pin is black and purple (like the tach) and the fourth is grey and red/brown. My thermotime switch has four wires coming out of it, unfortunately the colors don't match! It's hook-up is a mystery I haven't gotten to yet.
So the regular relay socket is for the WUR? How in the world did the car run well without it? Or maybe the relay just got lost when we pulled this thing apart.
Many thanks for your information. It is invaluable at times like this (when you are quietly going nuts) to get some real information!
Jim

spuggy · 10-27-2007, 05:48 PM

Quote:

Originally Posted by moneymanager

Hi John,
A capacitor?

Yup. You can see the rating written on the can (MFD = micro-farad, or mu-f). Don't wire it backwards, it'll either pop the can, or at least blister and not work anymore.

Quote:

Any idea where it might be wired in, or what it would be called on the
schematic?

The standard diagram symbol is to draw the wire, stop, draw two parallel lines perpendicular to the wire with a gap, and then continue the trace. In an electronics diagram or on a circuit board, it'd have a Cnnn component number.

Kinda like this:

----||----

In an automotive circuit diagram context, maybe it'd have a circle around the parallel lines, to signify it was a discrete component. Hope this helps.

Can't tell you what it's supposed to be connected to - on my car, I think the only part of that rear panel that's functional is the CDI...

304065 · 10-27-2007, 06:21 PM

The six-pin socket is a mystery to me. . . black/purple and red/brown, along with switched power and ground are all inputs to a SIX-pin Bosch CDI. . . did you pull this console from a '74, are you certain?

I give up, the Man from Texas will have to take over.

moneymanager · 10-28-2007, 11:45 AM

Thanks John. We swapped motors between a 73.5 and a 74. I am going to ask the mechanic tomorrow when I can see him if we swapped consoles too. I am pretty sure we did as I had an MSD on the other one and this one shows no signs of that.
But before I waste any more of your or anyone else's time, let me check.

DO you happen to know what the factory might have called the wur in the earliest CIS days (ie on the 73.5?)
My schematic shows no such animal but does show a speed switch (?), an electromagnetic control valve (might this be the wur?), a lifting magnet (aka a solenoid?), a time temperature time switch (which I assume we know as the thermo time) and a microswitch (which I think is the small switch at the left end of the CIS unit probably triggering the cold start valve.)
ANY contributions gratefully received. JIm

304065 · 10-28-2007, 02:00 PM

Jim you are looking at a mfi diagram

the wur is called wur, the pic above i posted is the factory cis addition

look at the sc diagram on the pp elec page

Early_S_Man · 10-28-2007, 03:22 PM

That suppressor was connected to the Voltage regulator.

The six-pin connector could be for a two-stage rear window defog relay ...

Strangely, none of the EMI/RFI noise suppression bits were ever shown on the factory schematics. I presume they varied somewhat from country to country, so the overburdened newhires [engineers] handling maintenance of the electrical system and documentation just never could quite get around to all of the needed projects! The parts did manage to make it into the parts catalogs, though!

This is a later schematic, but the two-stage defrost relay is the same, complete with internal error in the schematic! Easier to just put a transistor symbol inside the box ... than to get the drawing right, for some of those newhires, anyway.

moneymanager · 10-28-2007, 03:24 PM

Well no wonder it doesn't make any sense!
Let me study your diagram a bit. It may help on several fronts.
I have schematics for the 73.5 in Haynes, but they are so damned hard to read
(in b & w) that I have gotten used to some color ones someone posted on the web...but they are, as you point out, not for the 73.5. I see now on looking that Haynes actually has the small CIS chart you posted, but I prefer yours in color.
Thanks much for your help. Jim

moneymanager · 10-28-2007, 04:26 PM

Warren, thanks. If I can confirm this by tracing the wiring in the 6 pin connector
(only 4 of which are occupied as noted elsewhere in this thread) I'll let you know.

John, thanks much for getting me back on track. Now another anomoly. Looking at the "whole car" Haynes 73.5 schematic, the WUR gets power from rear middle fuse 2 DIRECTLY via pin 10 on the 14 pin multiconnector. But your small chart shows the exact same circuit EXCEPT that a "solenoid switch" with connections to voltage regulator pins D+ and D- is added between fuse 2 and the multiconnector.
I assume this is the correct wiring, not the whole car schematic.
But what solenoid switch are we talking about? Does it go under another name?
Jim

Early_S_Man · 10-28-2007, 06:01 PM

Jim,

Sorry, scratch the defog relay rabbit trail off the list ... I should have read a bit more about your wiring description for the six-in connector!

Without a doubt, that connector was for a Speed Switch [aka Speed Relay, RPM Transducer] for a carbed or MFI engine from 1968 - 73.

More details in this thread, if interested:

Tach - oh - woe (pre '74)

304065 · 10-29-2007, 03:44 AM

Wow, Warren nails it. Room for six pins in the headshell, but only four wires.

So do we think that the Factory left the wires in place in the console? JIT manufacturing hadn't been raised quite to the level it is to day, but I wonder whether it's truly a '74 console you have there.

moneymanager · 10-29-2007, 09:52 AM

Wow. Very impressive Warren. So I have an RPM transducer left over from mfi days? (Haynes shows it sitting there, p206.) And I don't need to worry about it anymore as it is non-functional? A big mystery resolved. Thanks to both of you.

Unfortunately I still have several unknowns. Here's one. John, I think it finally dawned on me that the #1 solenoid switch on your small CIS schematic is what most of us call the WUR relay? That would make sense I think. What still doesn't make sense is that my motor ran without it. Did later mechanics just bypass the relay having found it irrelevant for some reason?
Jim

Early_S_Man · 10-30-2007, 11:36 PM

JT,

My list of inclusive years for the Speed Relay should have extended out to 1976, for the 911/83 engine was built for the ROW 2.7 Carreras through the fall of 1975 ... for the last 125 or so.

The connector may have been in all wiring harnesses, but the module would not have been present in CIS cars. That would have been throwing money away, and including parts that weigh something, yet have no function on a CIS engine. Definitely a violation of the bean-counter mentality of 1974!

moneymanager · 07:21 AM

Again, many thanks Warren.
I've got another real mystery on my hands. Two red leads leave the harness on the rear console and dead end 3 inches later in a male shovel connector. The two wires show connectivity to the voltage regulator D+thru the frontmost 14 pin multiconnector (pin 12,) to fuse 1 at the rear, to the speed relay you just identified, to one of three pins in another unidentified small connector, and to a pin in the WUR relay socket. It almost looks like an aftermarket addition but the way it goes into the main harness suggests it is original. Any idea what this might be?
Jim