volts dropping

[klowninc89]

In my 94 suburban when in drive or reverse with my lights and heater on my volts drop alot. Also when defrost is on it dropped to red. No battery light. I never had a problem with starting my truck it has a new alternater on it and a big ass diehard battery. Idk what could be doing this everything seems to be working fine any ideas?

 

[4X4HIGH]

If your volts are dropping you should pick them up.

Seriously, the factory volt gauges aren't very accurate after 17 years of service. I would suggest you first get a GOOD DVOM and check the battery voltage with the engine off, then start the engine and check with it running (should be somewhere between 13.5-14.7 volts with the engine running). If the voltage is low then check directly at the back lug of the alternator and see what you have there with the engine running.

 

[Fordum]

The fan draws a lot of amps. Add in headlights, other loads, you may be just exceeding the output of your alternator.
Stock size is not always big enough.
The only way to tell for sure would be to know the wattage rating of the alternator and measure it under a load.

But if its a fairly large one, then check the usual suspects.

Bad ground on the alternator. Some people run a heavy cable from the frame of the alt to the ground wire hookup point.

Bad connection or too small wire coming out of the alternator.
If yours has a separate voltage regulator, it may be bad.

Plus, the one that used to be the most likely one, loose, glazed, or slipping belt.

Modern serpentine belts have mostly eliminated this one. I used to check it by running the car with everything electrical turned on for a couple of minutes.

Turn the car off, and Carefully touch the alternator pulley.
If the belt is slipping its going to be really hot.