88BlueTSiQuest

I went straight from the gauge to the alternator blue wire. A bit of a PITA, and as I stated, this should only be a temp fix to get it going.

Once again, this is only if:
A. The bulb check does not light when the ignition is turned on.

And:

B. The bulb itself is still good. A bad bulb would merely have to be replaced to fix this issue.

I simply used my multi meter to figure out which wire it was at the cluster plug, then cut it and ran it out to the alternator and connected it to the alternator's blue wire.

por4ever

Do you remember which pin you took it from the instrument cluster? Pin 3 connects to the ignition switch and the coil. Pin 4 leads to the alarm module and so does the blue wire from the alternator.

por4ever

I jumpered between pin 4 and the blue wire and it is still only at 12V. I have confirmed the bulb is good and the connection between the bulb and the coil is good.

project951

have you checked your belt if it is not tight enough it it will slip and the warning light comes on

por4ever

Ok after a full day of checking just about every voltage I can find I come up with this:

D+ - B+ Off->12.3VDC On .889VDC Running .824VDC
blue to ground Off .1mV On 11.2V Running 11.3V

I have the wiring diagram and I have an understanding of how the circuit works but it is a differential circuit and it is really confusing me. I don't know what the regulator circuit looks like so I am having a hard time telling if it is that or the diodes in the alternator.

You know the really sad part is that I am an Electronics Technician 2nd class in the Navy but it has been years since I have had to troubleshoot a circuit. I am a net admin type.

Droops83

If you have the back cover to the alternator off, the only reading you need is to, with the engine running, connect the positive lead of the voltmeter to B+, which is the alternator output, and the negative lead to the alternator case (ground). If the voltage is anything less than 13 your alternator is not working, either rebuild it or replace it, simple as that.

Also, as a side note, voltage drop tests are only valid if the circuit in question is active like Chris Prack said, in the case of checking the charging circuit that would mean engine running.

por4ever

Drove to work this AM and after the car had warmed up and I turned the lights on and reved the engine I got just under 14V on the voltmeter. Unfortunately I did not bring my multimeter with me. I will just take the alternator out tomorrow and have it tested.

I think she knows I am about to get my 914 running again and she is having a tantrum.

bearone

drive the car to autozone/checker/pep boys/etc and have them check it in the car.

87951

88BlueTSiQuest

Sorry, I didn't commit that one to memory. I used my multimeter to chase the traces for the bulb itself.

IIRC, it's the bulb's ground wire that ultimately connects to the alternator blue wire. The bulb lights up by using the alternator core as it's ground, and this energizes the alternator. Once energized the blue wire on the alternator no longer reads ground, and this shuts off the bulb.

Chris Prack

5mV is seems too low. I think you did something wrong. I would expect atleast 100-150mV on a normally functioning car. All wiring will have voltage drop normally.

The "idiot" light should come on key on engine off. If the bulb does not light you have a problem. The light bulb acts as an exciter for the charging circuit. Key on, engine off the bulb has power on one side and the alternator is providing ground on the other to light the lamp. Once the alternatror starts turning the power side of the bulb fields the alternator and both wires have power tuning off the light.

When you rev the engine over 3k rpm you are force fielding the circuit and it starts to charge. What I would do is remove the regulator and take a close look at the brushes. I bet you will find they are either worn down and are two short or they are worn unevenly. Either way you will need to replace the regulator.

You should be able to get one pretty cheap.

por4ever

Just wanted to update with the solution.

I removed the alternator and had it checked at Autozone and it showed good. I figured I would replace the voltage regulator anyway and when I took the old one out the brushes were worn down to nubs. I put the new regulator in and reinstalled the alternator and now I get a solid 14.5VDC.

Thanks to all for the help.

eniac

Glad to see you got it fixed.