Erratic amp gauge reading

[Keith M.]

I cannot get the amp gauge to function properly. At times it will show a very high over charge, never a discharge and some of the time it will shake violently. I have replaced the voltage requlator, ground the voltage regulator to the frame of the car and changed the alternator. If anyone can help me it will be appreciated.

[Douglas L.]

Re: Erratic amp gauge reading

Keith,

I had the same problem and tried everything. If you figure out, let me know. I finally ended up disconnecting the guage. The car still charges fine. I think it might be a ground.

[Keith M.]

Re: Erratic amp gauge reading

Doug,

Thanks for your fast reply. I ground the voltage regulator to the frame with no luck. Is there a ground on the gauge? Thanks

[Douglas L.]

Re: Erratic amp gauge reading

Keith,

There is a ground from the motor to the frame, from the bird cage to the frame, and from the dash to the birdcage, and there is the ground in the wiring harness.

I get steady charge at the battery. So, I think my problem is somewhere in how the guage reads that charge. My guage worked great for about 10 years after restoring the car. Then, it started to slowly go crazy. One time I pulled in for gas and noticed by quartz reworked clock was running backwards! It only did it one time - but somehow, I think the polarity in the electrical system got reversed!

[William C.]

Re: Erratic amp gauge reading

Keep in mind that the C-2 Corvette ammeter is really a very sensitive voltmeter that measueres voltage across the ends of the wire from the voltage regulator and infers charg from that measurement. Any instability in the system can cause "funny" readings while the charging system is functioing notmalle. One place to check is the connection between the engine wiring and the fuseblock on the front of dash under the master cylinder.

[Kevin G.]

Re: Erratic amp gauge reading

Might also want to check the wiring right at the alternator. It does become brittle from the heat.

Kevin

[Douglas L.]

Re: Erratic amp gauge reading

I worked the dash connector over pretty good by cleaning all the contact points and using contact grease and it didn't help. As far a the wiring itself goes, that's a good question. Brittle wiring can increase resistance.

What's interesting is at idle, the guage flops back and forth. If I turn on the lights, it flops back an forth more. When I increase the rpm's, the guage reading smooths out a bit.

[Keith M.]

Re: Erratic amp gauge reading

Doug,

Thanks for your input.

KM

[Keith M.]

Re: Erratic amp gauge reading

Thanks Doug.

KM

[Keith M.]

Re: Erratic amp gauge reading

Bill,

Thanks for your input.

KM

[Keith M.]

Re: Erratic amp gauge reading

Kevin,

Thanks for your suggestions.

KM

[Bill C.]

Re: Erratic amp gauge reading

I worked the dash connector over pretty good by cleaning all the contact points and using contact grease and it didn't help. As far a the wiring itself goes, that's a good question. Brittle wiring can increase resistance.

What's interesting is at idle, the guage flops back and forth. If I turn on the lights, it flops back an forth more. When I increase the rpm's, the guage reading smooths out a bit.

Having same issue with a car, alt good, VR good, gauge good, grounds good, firewall connections good, BUT it is the original wire harness, appears as good but inside?

[Phil D.]

Re: Erratic amp gauge reading

I had a jumpy ammeter on my 69 and ultimately discovered a spot where the insulation on the positive cable to the starter had worn off and it was occasionally arcing to a nearby ground. Fixed that an the meter has been steady since.

[Douglas L.]

Re: Erratic amp gauge reading

Phil,

Thanks - I will check that one out.

[Jack H.]

Re: Erratic amp gauge reading

And, the voltmeter in the gauge is rather cheaply constructed...

If the gauge itself has seen prior electrical overstress, it can become intermittent in terms of pointer needle operating integrity. This can be verified on the bench...

You connect the ammeter to a variable bench power supply and raise the voltage output from 0 VDC to roughly 1/2 Volt. The pointer needle ought to move smoothly, in lock-step from its center position to either the +40A or -40A gradicule.

Reverse the cables and re-run the test. Now, the pointer needle should swing smoothly in the opposite direction.

If the pointer jumps or becomes unstable, on the bench, there are gauge internal problems you're fighting. If the gauge moves smoothly and is rock solid, you've got problem(s) in car's wiring harness components and/or the voltage regulator/alternator...