Voltage Problem

TAH0129

MEMBER
GMC C1500

I have a 86 GMC Pick-up C-1500 305. I have replaced the alternator and battery. My battery meter always stayed at 13 volts. I noticed it was going down so I replace the battery. After it was still going down as I idled at a traffic light I replaced the alternator. Now when it idles the voltage meter still goes down almost into the red. I have check all grounds under hood. What could be wrong?

1 Reply

MHPAUTOS

MECHANIC
31,937 POSTS

Hi there,

You will have to check the out put voltage at the alternator do this with all acc turned off, then check with head lights and heater fan on. If voltage is stable at alternator, make sure that all the earths are tight and in good condition, set a master amp gauge up on the battery pos, and check amps there, don't rely on the car's gauge as it may be faulty. Load test battery and check with a hydrometer to prove battery condition, if the alternator is working as it should the problem is in the wiring IE a faulty connection, bad earth or faulty amp gauge. I am not to sure but check if your car has an external voltage regulator, if so the problem could be there, and not the alternator itself.

Mark (mhpautos)