73.5 charging light problem

[cak]

I've got a new-to-me 73.5 911T. Since bringing it home (from Portland to Palo Alto), I've been attacking various small electrical problems. After today's session, I decided to go for a ride. Car hasn't been started for a month, the battery disconnect has been off, so the battery is in good shape.

Start with the usual CIS dance, but the big red charging light won't go off.

It did something similar to this 6 weeks ago when I was picking up the car from a year's storage. Then, the light stayed on when the key was off. The battery was flat then, and we towed it to a shop that diagnosed a short in the alternator. Three hours of labor and an alternator rebuild later, I was on the road.

Now this. If I was still in the same state as the shop that did the work, I'd just drive it there - but I'm not. Suggestions welcome. All I can do without tearing into the shroud, I think, is verify that there is no voltage at the regulator terminal - and there isn't (well ... my test lamp didn't light at the blue wires).

I put a voltmeter on the battery and it is not getting charge when the car is running (12.4v off, 11.8v running).

I tried tapping on the regulator in case something is stuck, to no avail. It was tested OK in early December. I checked the list in "101 projects", but it doesn't really tell me how to determine if the regulator is OK or not. It's a Marchal regulator, presumably original, which I think means I have the 70A alternator (but I'm not sure, and the paperwork I have doesn't say).

Suggestions? Maybe some connection has worked its way loose under the shroud?

Thanks,
chris

[cak]

I measured at the regulator terminals: with the engine running and the charging light lit, there's about 1.5V at both the D+ (blue) and DF (black) terminals. D- is well grounded (0.4ohms to engine casing). There's B+ at the 25A fuse.

I notice that the D+ has an extra black wire that was added at some point; it disappears into the structure of the box there, but I haven't yet traced it any farther. The 14pin connector seems clean and solid.

Seems like maybe the regulator has failed - is there some test I can do? The schematic (and Haynes) don't really tell me much about its inner workings, other than that there's a coil - I measured about 5ohms to ground with power off from both D+ and DF, but that is not enlightening to me.

[Early_S_Man]

Chris,

Is it a metal-cased regulator, or one of the rectangular, plastic ones? 1973 and earlier cars came with the oval, metal-cased Marchal/Motorola regulator and 55 Amp, 770 Watt alternator. The 980 Watt, 70 Amp alternators did not appear until late-1975 production, and there was also an 840 Watt interim model, as well, in 1975 early production!

The metal-cased regulators are relay-based, and are adjustable ... after the case is removed.

[cak]

Metal cased, silver or cad plated, marked SEV Marchal.

It looks as if the cover is "just" snapped on with a couple of indented points, but I wasn't able to remove the cover with the regulator in place - but I couldn't apply too much effort there.

I plan to pull it tonight and see what it looks like inside, burnish the points, etc.

And charge the battery with an external charger.

I'm thinking about full-fielding to test, since the alternator was just rebuilt for $$$ and I would rather not pull it if I can avoid it.

Thanks,
chris

[304065]

The "extra" black wire sounds like an add-on by some prior owner, can you post a photo? Often the blue wire turns black with age, though.

The plug at the bottom of the VR has three terminals, as you can see in the below diagram:

http://www.pelicanparts.com/911/911_Parts/Electrical/911_electrical_1973_CIS_Part2.jpg

If you examine the diagram, you will see that the blue wire starts at the battery, runs to the ignition switch, goes to one terminal of the bulb holder and then back to the VR, and then to the D+/61 terminal on the alternator.

The DF goes directly to the alternator rotor, hence its title "DF" or Dynamo Field.

Finally, the brown ground is connected in two places, one on the alternator, and one on the chassis, probably to make sure there's no potential difference in the sensing circuit.

Now, when you turn the key on, the voltage coming out of the alternator's "trio" diodes is less than +12v, so current flows from the battery through the bulb, lighting it, and then back to the voltage regulator and to ground. It doesn't flow into the alternator because the trio diodes block current flow "in," they only let current flow OUT of the stator, more on that in a minute.

At the same time, the +12v coming from the battery causes the VR to drive the DF current to maximum, in order to induce a magnetic field in the rotor windings.

Now you start the car, and the field induces an alternating current in the stator, which is rectified by the trio diodes and fed OUT of the alternator in the form of a voltage, which is higher than the battery, around 14V. Since there's more electrical "pressure" on the alternator side, current flows in the other direction, back toward the battery, and since the pressure has dropped by the time it gets to the bulb, the bulb won't light. The light goes out. At the same time, the VR reduces the amount of current flowing to the field in the DF circuit, and so the output voltage falls, causing the "trio" output to be lower, which reverses the current flow in the blue wire circuit, causing the whole thing to start over again. It's a continous feedback loop from the alternator's output, all centered around the "set-point" or desired output voltage from the main diodes (B+).

The below diagram may make this easier to visualize. Notice how the regulator has one leg going to the Rotor (DF) and one leg going to the battery (D+/61) but also connected in parallel with the output diodes (the "trio).



Your first problem is too low a battery voltage. You should charge the battery unti you have 12.6V resting voltage.

Where, exactly, does the extra wire go? Remote diagnosis impossible if a PO has changed from the factory setup.

[cak]

Thanks, John. I'll put the battery on charge when I get home, and then start over. Is too-low B+ likely to produce this symptom? I understand that the alternator is not really designed to bring a dead battery back (it's an Odyssey, btw).

I'll also take a picture of the extra wiring, and do a little tracing - I was in a hurry this morning. It's added to the faston tab with the blue wires by using a piggyback male/female terminal, then goes down the same path as the blue wires, and into the folded metal base that holds the various pieces together. I can see something in there wiggle when I wiggle the black wire at the regulator, but I didn't investigate beyond that ... but I think that it goes to another insulated spade connection down in there.

I'm trying really hard to avoid pulling the alternator if that's at all possible ... in case you hadn't noticed. I know that it would be good for me, but not this week, please. :-)

[cak]

OK, I have data on two things this morning (brr, I need a bigger garage ... at least it's not raining any more).

First, the mystery wire. You want pictures? We got pictures.

First, a general overview of the area:



Now, the regulator's upper connections (sorry about the focus):



Now, the regulator's lower connection:



And a view into the chassis:



It appears that the extra black wire that is connected to the D+ and the extra brown that is connected to the bottom mounting bolt go into the chassis, to the insulated faston connectors visible under the rd/wh wire, and continue into the harness for the relay socket, along with a rd/wh and rd/bk wire. My best guess is that this is the rear defogger relay, and that the well-known 1973.5 911T schematic is a bit out of date as to where terminal 86 actually gets B+ from.

Not too interesting, in retrospect.

On to the charging system! Battery was on charger over night, disconnected via the battery disconnect switch (in the ground lead). Some voltage readings, measured at the battery...

batt disc off: 13.04v
batt disc on: 12.85v
ignition on: 12.1v
engine running: 12.1v
ignition off: 12.4v

Charge light comes on with ignition on, stays on when running. Oh well.

I put the battery back on the charger.

I have connectivity from the battery's positive cable to the blue tab at the regulator. I didn't measure resistance, just listened for the beep.

I pulled the regulator. I'll take it to a shop to test. I pulled off the top and inspected a bit - the points have some fuzz, but I've seen worse. They certainly aren't stuck together, and they have low resistance.

For grins, I tried hooking up a power supply to D+ and ground. I have a small variable supply that's limited to 0.5A, and it clamped before I got to 12V. I could see the arm deflect, but not enough to move the points. I then tried a fixed 13.8v supply which does about 5A, and it deflected further, but again not enough. I don't have anything that puts out higher voltage right now, but it appears that I was getting close to causing a switch.

This is ... puzzling to me. Is the rest position to provide a connection between D+ and DF?

Anyway, I'm hopeful that it's the regulator, but I'm betting that it isn't, and I'll have to pull the alternator to look for a loose connection or worse.

Thanks,
chris

[304065]

Chris,

Classic VR meltdown. The old mechanical VRs can fail over time.

Check out the Transpo IB301A.

[Early_S_Man]

Chris,

That round black relay isn't for the rear window defogger ... you have a two-stage defogger relay in the aluminum rectangular box by Hella, as depicted below. I believe the 'mystery' brown and black wires are for the CIS Warm-up Regulator relay as shown below in the CIS Addition schematic from the Pelican Electrical Diagrams page.

[cak]

Thanks, John.

Looks like the Transpo ID4010 is the right modern replacement for the Marchal regulator - they cross reference it to the Porsche p/n 911 603 901 00, but not to the 724 161 02 that's on the case.

And our host carries it!

Seems a pity to put a solid state regulator on a fairly unmolested original car...

[cak]

Thanks Warren! Yes, that makes sense and matches what I see. Not shown on the Haynes schematic which claims to be for the 73.5 CIS 911T ... oh, there it is, on another page!

So where is the warmup regulator and what does it do? I guess that's really a different thread. :-)

[cak]

OK, local electric shop tested the Marchal regulator and says it's overcharging to the tune of 17v!

And that may have fried a diode in the alternator, leading to no charge at all.

Bother.

I guess I have nothing to lose by momentarily full-fielding the alternator to test it?

[cak]

I guess I have nothing to lose by momentarily full-fielding the alternator to test it?

And apparently nothing to gain - no obvious change. I have a new voltage regulator on the way.

I guess I'll be learning what it's like to pull the alternator after all.

[304065]

Removing the alternator is a 12 minute task to get it out of the shroud, and another 10 to get it out of the fan housing. Search here for John Walker's Famous Wooden Box Technique.

Be sure and make note of the number of shims inside the pulley, and the number outside, between the cup-shaped washer and the pulley. Do not fail to note the number.

[cak]

Removing the alternator is a 12 minute task to get it out of the shroud, and another 10 to get it out of the fan housing.

How long did it take the first time? :-)

Failing on the wooden box search, I fear, but I'll keep looking (and read all the various writeups).

Thanks,
chris

[cak]

Well, OK, it took me about 30 minutes from start to bare alternator, even with the a/c belt and grabbing the wrong socket a few times. Not bad at all. (Yes, I counted the shims.) I don't have a suitable wooden box, but the steps up to the deck are wooden and worked adequately well.

Yes, it appears to be a freshly rebuilt SEV unit. Not even a little dirty.

The alternator is at a local shop for test/repair. Initial testing didn't reveal a bad diode, but... we'll see. She said she didn't like something about how the rotor looked.

One thing I noticed is that the blue wire from D+/61 on the regulator was not connected to the terminal marked D+/61 on the alternator (which is on the raised bridge/brush plate with the B+ terminal), but rather to a (insulated, unmarked) post that is lower down on the body of the alternator. I mentioned this, they didn't know, but will check it out.

While I've got this apart, what else should I be looking for? I guess I could pull the a/c bracket and read the engine number... but I'm thinking more along the lines of continuity tests and visual inspections

[cak]

OK, finally back together... took a little longer because I had to do some shroud repair around a rivet hole. Thank goodness for JB Weld. Getting the ground strap back on is a pain.

Alternator didn't have a bad diode, but didn't work. Lady at the shop (Pacific Auto Electric, Sunnyvale, Calif, great folks) said that the brush path looked "funny" - not an even path of graphite. They cut the commutator and it's working ($20). Her best conjecture was that the 17V cutout of the regulator was causing some internal arcing and that caused bad/no contact at the brushes. Dunno. "Working now..."

Installing the Transpo ID4010 was a small challenge. The mounting and terminals are close, but not quite.

Here's a photo that compares the two regulators:


For starters, the terminal connectors aren't the same. That wasn't hard to fix. But the CIS addon harness for the warmup regulator relay is quite short, and uses the case of the regulator as a ground path. That doesn't work on a plastic case!

The overall 'vertical' dimensions are larger; the terminals stick up higher than the original, and the upper mounting hole is at the very upper end of the SEV's upper slot.

The main regulator harness comes up under the left side of the regulator (see pic earlier in the thread). The ID4010 has a full-width bottom mounting leg, so I cut some of that away for clearance. I made a ground jjumper to go around the other side (and had to carve a little clearance there, too).

Here's the final install:



Seems OK so far. I added some plastic edge strip to keep the black CIS wire from rubbing on the chassis - I don't want to wear through a B+ lead (you can't really discern it in the photo, since it's the same color as the dirt next to it).

I'm a bit concerned about the added stack height on the two mount points, especially the top one; the plastic legs are thicker than the original steel, and the top one has the regulator's ground strap *and* the extra ground jumper.

It's worth noting that the set point on this Transpo is 15V; that seems like it might be high, but I guess they're counting on significant voltage drop between the alternator and the battery. The ID4009 has a 14.3V set point - but that's not the part that 'everyone' sells for this application.

The best news, of course, is that the red light finally goes out again!

Thanks for everyone's help.

[azasadny]

Chris,
Good luck with the new car, looks like you've got things under control.

[cak]

Wanted to link this to another alternator thread

Alt light doesn't work

which implies that anyone doing this change (from mechanical to solid state regulator) might want to add a resistor to the charge indicator lamp socket as described in the Factory Technical Bulletin listed there.

I did so and am happier with how quickly the alternator/charge light goes out at start ...

[Sunroof]

So, you asked about the warm up regulator (WUR)?

Hey Cak....

The WUR is mounted on the left side of the engine next to the intake manifold. Its easy to see if you look in that direction. Small rectangulat metal shaped thing held mounted to the block by two bolts. It has a ground wire (black) and a hot wire (red?) that runs to the relay as well as a connected fuel hose. This little gem has been the unit from "hell" for many and can be a big problem on cold start - warm up issues. They are adjustable and often require high - low fuel pressure adjustments. Inside this little very expensive regulator is a metal bar that heats up and opens to allow proper fuel flow during warm up. They can be bought rebuilt and often the original 73.5T unit is almost impossible to find, so you can replace with a newer unit (from the 74 on series). Your right in saying the WUR in "another issue". If you own a 73.5T then get ready to experience the infamous WUR chapter as time progresses. These things make you feel like you have a 70's car!!

By the way, I replaced my v-regulator with a Bosch replacement (metal) that cross references with the older unit. Cheap and suitable replacement and easy plug in. Keep all those contacts back their clean!!

Bob
73.5T