85fortheDrive

With no key in the ignition - 12.6V between exciter cable and alternator housing
With key turned to 2nd spot, just prior to starting the engine - 0.75V between cable and housing.

Is this abnormal?

Also, when key is turned to second spot, the emergency brake (!) light and the light at the bottom of the oil pressure gauge both are flashing.

Tyson and I are trying to figure this one out.
Any ideas?

Time to pull the pod?

Tyson wants to know if a Playboy centerfold can act in replacement of the exciter circuit.

Lizard928

if you have the option (be very careful) check the voltage while running. That is the ultimate test.

I normally use a pair of wires with alagator clamps on both ends, one end of each on what I am testing and one on each of the tester leads.

However it sounds like an ign switch issue if that is the case.

85fortheDrive

I had the car into a shop yesterday and they tested the car twice while it was running. The first time, from a "cold" start, the alternator put out a steady 13.9V. They were about to tell me that nothing was wrong when they tested it again. This time, the alternator was putting out 11.7V - not even enough to charge the battery.

I recently replaced the ignition switch because several Rennlisters suggested that as a likely culprit to these gremlins. I suppose my installation could have been faulty, but I know there's a new switch in there.

j.kenzie@sbcglobal.net

I don't think your ignition switch install is bad. The connector is all or nothing more or less. There is a pathway from the instrument panel to alternator with a defined resistance through a light bulb. This could be faulty any of a number of places.
Good luck

Alan

Tim - with ignition off it should be 0v between the exiter wire at the alternator and ground. It should be approx 12v between the alternator big terminal (battery+) and the alternator exiter terminal.

When the ignition is on and car not running you should have a small voltage (a few volts? - 0.75v seems low) between the alternator exciter terminal & ground. When the car is running the exciter terminal should virtually match the output of the alternator = big terminal

Make sure you know if you are measuring to ground or the the big alternator terminal...?

Alan

FlyingDog

If you start the car and voltage is low, then rev the engine... does it start charging? Does fully charged vs partially charged battery have an effect?

Charley B

This certainly sounds like a voltage regulator problem. I'm not so sure it's related to the issue occuring with the engine not running.

85fortheDrive

Nope, with the key out, I get a 12V differential when I put one voltage probe within the exciter wire ring and touch the other to the metal chassis of the alternator.

I will check this next.

As reported, I do.

I will measure voltage between big terminal and ground as well as exciter terminal and ground.

I was using the chassis of the alternator as the ground when testing voltage differential on the exciter wire.

Continued thanks. I am enjoying learning this stuff and know that I have some great tutors here.

Pax,
Tim

85fortheDrive

I'm holding off on having Roger send another replacement alternator until we test all possible wiring fault possibilities. But that remains a possibility Charlie.

Thanks.

Alan

Tim - I think you need to remove the wire from the alternator exciter terminal.

Measure the voltage on the alternator terminal - still ~12v? if yes - seems the alternator is kaput and is driving this line itself all the time - it should not unless its spinning & the rotor field was initiated. (Some units may self initiate at hig rpms)

Now measure disconnected exciter wire with the ignition off - should be 0v? Now measure with the ignition on should be 12v? if these check out its likely the pod wiring is good and not part of the problem.

Alan

ROG100

Alan - Alternator is a new Bosch remanufactured unit - some similar problems were being experianced with the older alternator. I have another one ready to go but we do not want to throw parts at the problem.
As you know I'm a little electrically challenged and trouble shooting from a 1000miles is always tricky.

85fortheDrive

Okay, day off of work here today and a chance to make some progress...

Alan, I'm trying to make sure my measurements aren't making the matter more confusing. All of my tests thus far on voltage difference between exciter wire and ground have been done with the exciter wire unfastened - I connected the probe to the interior of the connector loop in doing so.

This morning, I have measured voltage between the two terminals on the alternator with the key out of the ignition. With exciter wire off, it understandably reads 0V. With exciter wire attached, it reads 12.6V. When I insert the key and turn to position 2, the voltage difference between large and small terminals on the alternator WITH THE EXCITED WIRE ATTACHED is 0.75V. With the exciter wire UNATTACHED and the key in position 2, the voltage difference between the terminals is 0V.

I hope I'm doing the right homework here.

Also, I do not see all dashboard lights come on when I turn the key to position 2. Just the two aforementioned flashing ones. So I'm ready to take the pod off if necessary.

Oh, good morning Tyson.

Alan

Check the fuses for the dashboard - #4 & #12 I think ?

Alan

85fortheDrive

4 and 12 are correct - both 8A. Replaced them, but same situation.

Fellow Rennlister and good pal Dave McKenzie assisted me in the installation of a new Commando car alarm/keyless entry system last weekend. With the fuse in or out of that system, the behavior described in this thread is the same. Just wanted to let you know of that change to the car since it is electrical in nature.

In the low 30's here in Chitown. Had to turn the space heater on in the garage. Continued thanks.

Jim bailey - 928 International

Odds are the front engine harness is toast ! The big alternator power feed wire to the jump start post and oil pressure wire as well as starter wires are bundled together. The insulation has cracked and wires are cross feeding. That often happens after it is worked on and the harness moved around like during a timing belt change.