3G Current Draw???

[Chalky]

Chasing an electrical gremlin in the '86. I noticed the battery was discharging so unplugged it till I could diagnose it. At Mitch's suggestion I put a meter between the + battery terminal and the + positive battery lead and measured 4.2 amps. I then proceeded to remove fuses one by one but saw no change on the meter.

Then started to remove connections from added accesories, PLA headlight relay harness, added gauges etc.

The only time I saw a change, draw dropped to 0 amps, was when I removed the 3 pin voltage regulator harness from my 3G alternator and when I removed the large yellow wire (part of chassis harness,primary power??) from the + side of the starter solenoid. The 3G was still connected when I removed the yellow wire.

I am thinking it's time to replace the alternator?? Any thoughts??? It's charging fine and the battery holds voltage with the voltage regulator disconnected.

[Laredo]

Are you sure it's charging "fine?" If you have a bad diode in your rectifier bridge you can end up with 2/3 charging output (1/3 of your alternator windings are dead). If you have a good battery and not much amperage load, your charging voltage would still be relatively normal. A shorted diode (which happens) will allow the current to flow backwards through your alternator to ground. 4.2 amps sounds about right for this kind of draw. You can also see it on an oscilliscope pattern of your charging system. Or...just replace the alternator.

[MikeFleming]

The EEC KAM (keep-alive memory) and most modern radios in powered-off mode will total to less than 0.8Amps in my experience.

As Laredo suggests get a scope on that alternator output (under load) and see if it's a proper rectified sine wave. You will not be able to detect bad diode(s) in an assembled alternator using a voltmeter.

[Chalky]

Well, couldn't find a 'scope at Wal-mart or the local Goodwill so I just swapped the alternator. Gotta love lifetime warranties:):) Well, still measuring a current draw so I'm gonna have to dig a little deeper. Any suggestions??

On a positive note, the new alternator does seem to have woken the car up a bit.

[Under Pressure]

Put a test light between the positive cable & battery key off. If you have a current draw the light will be on. Then start around the alternator and start disconnecting wires until the light goes out. If it doesn't go out disconnect everything on the car til it goes out. It can take some time but you'll find it.

[SnakePlisskin]

Do you have one of those ghetto blaster stereo systems?:stick_poke:

[Chalky]

Nope. Currently the car has no stereo, passenger seat, centre console or any other interior to speak of:):):)

[Laredo]

Have you pulled fuses?

[Meotchh]

Put a test light between the positive cable & battery key off. If you have a current draw the light will be on. Then start around the alternator and start disconnecting wires until the light goes out. If it doesn't go out disconnect everything on the car til it goes out. It can take some time but you'll find it.

That is the poor man's method of what he already did with a DMM. With the DMM you can actually view the current drain taking place.

[Under Pressure]

Yeah test light cost a couple of bucks. I've used that method for 40 years works ever time to find a 12 volt current draw.

[Meotchh]

Yeah test light cost a couple of bucks. I've used that method for 40 years works ever time to find a 12 volt current draw.

I'm not saying it doesn't work, but I prefer to see how much current is being drawn. Many times it helps to troubleshoot the offending component knowing how much current is being drawn. But if you only have a test light, that will work to assist in finding the source of the problem

[Chalky]

I just got back from a week snowboarding up at Mt. Baker, WA. Awesome time with Sada for her 30th Birthday. Gonna get back onto this this week and see what I can find.

[Chalky]

So, finally got around to this and think I've solved the problem. I've had the dash bezels out since I got it and forgot which idiot light was the amp light. I'm well aware of the "amp light bulb blows, no charge" scenario, but was getting a good charge so figured it was something else. SVOJosh was around today helping me finish the brakes on the 8.8 and we decided to trouble shoot this. Looking at his car I realized my amp light was blown. Switched the bulb with a known good one, still no glow.

At this point I decided now would be a good time to switch my cluster over to the white face gauges from Blackie. Easy, I thought, switch over the printed circuit board and away we go. Turn's out there is a resistor or something mounted to the housing so we pulled both clusters apart and put the white faced gauges from the 84 cluster into the 86 cluster. With that done we went to re-fit the cluster when I discovered that the lower left harness connector, the one that goes to the idiot lights, had a tab broken of and wasn't locking in place properly.

Switched it out for a good one, got it all back together and fired her up. Lights all lit up, except the low oil (which is good right:) ) and she seems to be fine. Charging and 14.4V, steady at 12.7V when off and no measurable draw with a meter or test light.

Here's the confusion, I've fixed charging issues with switching in a good bulb before. I know the system won't charge without the amp bulb not working, but I never knew it would discharge the battery if it was blown. Anyone else had this situation before??

[Desert Patina]

Its funny how the universe works. I was diagnosing why my alternator won't charge, and going over wiring schematics and thought, "hey, do I really see what I think I see? The alternator won't charge if the light burns out". I guess I really did see that.

Also, while playing with out cluster this week, we found that a simple pinch on the plastic printed circuit on the back of the cluster will cause a short. Perhaps it is possible that your cluster had a similar short along with the burned out light?