Question for all (especially the elders. I'm not worthy). I've got a '90 RS that is O.K. cold. 14.5V. As I drive it the voltage gauge gets lower. It will go below 13 and approach the 12.5 that the new battery is sitting at. Also the voltage bounces slightly to moderately with bumps on the road. My wife and I first noticed the low voltage condition with full load, lights, AC, @ Idle in gear. I also had some weirdness in the headlight switch. When turning to dome position voltage display would go to 15V. Release then back to 13 - 14V. I've changed out:
Battery, Alternator, Headlight switch, relamped all exterior bulbs and actually got another Instrument cluster. Now the voltage still lowers as you drive but without full load involved. The voltage still bounces from 1/2 to a Volt when going down a rough road. I've been working on cars since I was a kid, but this one has got me scratchin' my head. Sounds like a loose connection, right? The batt cables look good. The 12V distribution block is tight and clean. The main chassis ground is tight & clean. Please offer some advice. Check alternator mounting and alternator output to confirm behavior is real not just a gauge behavior is what I've gathered so far browsing this forum. Any help will be greatly appreciated. Thanks in advance.

BTW I've got a ton of experience with other Camaro issues, having had them for 31 years. Feel free to ask me any questions you may have. I'm more than willing to contribute to these boards.

T

 

The factory gauges in these cars are terrible, so don't count on diagnosing any problems from them. Mine reads a hair over 14 an times and other times at 12, while my aftermarket gauge reads a steady 13.5.

 

Sounds like you have a gremlin that's one step ahead of you!
Have you checked with a test meter both at the alternator and the battery to see if it drops the same as what the dash gauge is showing, and to also see the voltage difference between the two? You should have at least 14v coming from the alternator, and 13+ at the battery with no accessories on (some voltage drop is normal going through the system). With the headlights, fan, etc. on, voltage at the battery can drop to the 12's.

 

I sometimes out smart myself. Did some measurements last night.
The voltmeter gauge is lying to me. The battery and the alternator are very close together in their respective readings. I did note that I got a 13.4V from the alternator at full load. Just once though, the rest of the time it was 14.3V. No I'm not dyslexic. I've got a lifetime warrantee on that bad boy, so I'm thinking of getting it tested. They can't test under load so if I push they will cough up another one. Thanks for your advice Camaro 69. I'll keep posting until I get this resolved and I'll let you know what I found. Right now the negative battery cable is my strongest suspect.

 

Cables coming in tomorrow. Installation on Saturday.
Can't wait to get "Sally" back on the road.

 

Cables are in. $60 cables thru local College auto department friend for $34. So far, so good.

 

The cables are installed and it looks to have been a failure of the insulator, not the conductor. Cleaned up 4 grounds. Main ground batt cable to engine block. Neg batt to chassis ground. Engine to firewall ground. 3rd point altermator to mounting bracket. That and new positive cable to starter and positive cable to 12V distribution block. 1 badly gouged finger later and about 1 hour total working time it appears we have a winner. So far all voltages both real and the display an the gauge cluster are solid as a rock! Woo-Hoo!!:ic on_jammin: