1G Strange voltage issues with aftermarket voltage gauge

[kchaazz]

So, when I got the car put together, I rewired the alternator from the B+ post to the battery fuse with 2 awg wire (I had some laying around), then 2awg from the fuse to the battery. Ive got the high output, Canadian spec alternator. Ive also got an Autometer Sport Comp volt gauge, which is tied into the fuse box under the driver's side dash, in a slot that was unused by the factory but comes on when the ignition is switched on.
Anyway, over the last couple months, Ive noticed that the volt gauge, which usually stays around 13.5- 14.xx, has a dancing needle that is going down to 10- 12 volts then going to 13 or so and changing constantly. If I put my multimeter on the alternater when the gauge is doing its thing, the alternator reads a steady 14.2- 14.3 volts. However, when I put the multimeter on the battery posts, it will sometimes be at 13.5 and sometimes down to 12.xx volts. Battery is an Optima Red Top, but I got it October 2012, so is it ready to be changed or? Car always starts and fires right up, its never drained even when its sat for a month. I just cant quite figure this one out.

 

[hotrodssnova]

Have you checked at the fuse, both sides, and at the terminal before the battery. Sometimes the wire will corrode inside the cover and give you odd readings.

 

[kchaazz]

Well, none of my stuff at the battery is even stock. Its all that tin plated, amplifier crap that supposedly doesnt oxidize, and it all looks good. Basically, instead of the 3 fuse block on the battery, Ive got a distribution block that takes 3 either 2 or 4 gauge in, and 3 8 or 12 gauge out. So, from battery fuse, 2 gauge into the block, then one of the inputs goes to the starter then one to the battery itself, then I used the 3 fused outputs for the 3 factory wires that used to go to that fused block. Here is a picture. Im going to check voltage on each side of the battery fuse this weekend if I have time. Maybe Ill put the voltage gauge directly off the battery on a relay or something too.

 

[stars]

Go back and double check all your connections that you yourself have installed. Something more than likely a ground issue with your aftermarket volt meter is causing the gauge to not read the proper voltage. (Keep in mind you could have a faulty gauge) Since your alternator output with the multimeter is of an constant voltage I would highly suspect the the gauge itself may have a problem. You have verified that the alt output is of an consistent voltage compared to what your gauge is interpreting. Go back and double check connectors and the proper placement of the grounds on your custom wiring job.

 

[kchaazz]

Actually, the gauge was reading ten vols and the the starter was barely turning the motor over today so i think perhaps the alt was putting out 14 volts but not adequate amperage to actually charge the battery. Going to get a new alt from JNZ and see what happens

 

[kchaazz]

Okay i figured it out. I decided to poke around with the multimeter some more before buying an alt or battery and this is what i found. The slot in the fuse box under the dash that i had the guages tied into was outputting unstable voltage. I found another unused slot that has power always even with the ingnition off and it reads 12 volts with the ignition off, and 14 plus with the engine running, so i installed a relay and used a slot that comes on with ignition to turn on the relay and the constant power slot to power the relay and tied the guages to the relay and now the voltage guage reads 14.xx volts when the car is running. Regarding the unstable voltage and the starter hesitating intermittantly, i can only guess that a weak ignition switch may be to blame but for now i will consider this problem solved.