1969 Z11 Pace Car. 350/manual/AC. At idle the Gen light in the dash flickers and the amp gauge in the console shows negative. At higher rpm light may go off but amps are still negative. New: alternator, junction block, voltage regulator, horn relay, battery cables, ground straps, amp gauge, etc. This problem has also stumped the local muscle car shop. Battery dies after a ride of 45 minutes or so.

I would appreciate thorough suggestions on best way to troubleshoot this. Been a problem for 12 years that i have owned it.

 

Hook up a 10 ga. wire from the output terminal on the alternator, and run it directly to the battery. If that solves the problem, then you have a wiring issue. The factory output wire from the alternator splices into a main wire inside the loom further down the line. If that connection is corroded, or any of those related wires are cracked/frayed/corroded, you'd have resistance in the line that could be holding back power that should otherwise be going to the battery.

 

Thanks for your response Camaro 69. I tried as you suggested and it made no difference - isn't that weird? I think I actually tried that same jumper several years ago, but it was worth another try. This is a new alternator - new a few years ago, probably has 100 miles on it - and I have since taken the alternator to AutoZone for bench testing. Also swapped out a few of the voltage regulators.

The Gen light is actually on half dim but steady at all RPMs.

I'm thinking I must have a short somewhere and was wondering if this would work if in fact I have a short - should I start the car, then one-by-one remove each fuse in the fuse box and check to see if it makes a difference. Wouldn't that at least isolate the circuit that has the short?

A little more observation in case it helps - when the car is running the gen light is glowing and the amp gauge is reading maybe -2 amps, just left of zero. While running, if I turn on the direction signal, with each blink the amp gauge drops to maybe -4 amps and back to -2. If I turn on the headlights it drops to maybe -10 or -12 amps. Hope that might stir a thought.

 

Have you checked the voltage output directly at the alternator? That would at least narrow down which side of the charging system you need to check. I'm thinking another possibility is that the voltage regulator might not be getting activated. I know you replaced the horn relay as well as the regulator, but did you check for battery voltage at those two points?

 

Thank you for sticking with this a bit longer. I assume to check voltage out at the alternator I just use my multimeter from output stud to ground? I have not specifically checked voltage at the regulator and relay - I'll check that too. Thanks.

 

The voltage across the battery is 12.55V. From heavy red lead on horn relay to ground it is 12.51V and from heavy red lead on regulator to ground it is 12.46V. Going from output stud on alternator to ground I'm getting 11.91V. In all cases ground means chassis.

 

With engine running? That's how you want to check the alternator output.

 

Yes, engine was running to get all of those numbers.

 

Well that's not right! With engine off, carefully disconnect output wire from back of alternator, and see what kind of voltage reading you get on that wire.

 

Another thing to check, make sure your alternator and regulator have good grounds.
Also, while the alternator output wire is off, check to see what the alternator is putting out with the engine running.
This pic shows your charging system in a nutshell. Really not all that complicated once you look at it. Since you replaced everything in the system, without change for the better, your issue must be with the wiring somewhere (assuming your replacement parts aren't defective). There is an off chance that you got your hands on a bad alternator or regulator. Don't always assume new means good.