Headlights drawin juice from fuel pump


Asked by May 24, 2015 at 07:59 PM about the 1994 Chevrolet C/K 1500 Sport Stepside 4WD

Question type: General

I've got a 94 Chevy 1500. I was goin to work one mornin and hit a pothole. The lights
dimmed down and the truck started to dog then shut off. I got it to work and then looked
at it after I was done. The truck runs great until I turn on the headlights. It brings my
battery gauge way down and draws enough power from my fuel pump that the truck will
spit and sputter then shut off after a couple of minutes. Keep the lights off and it runs
great. Changed the battery and had the alternator tested 5 times. Checked and cleaned
the grounds. Still can't figure it out. Anyone have any ideas?

13 Answers


Check the power wire that goes to the power distribution box, you may have to remove the box enough to look underneath for damaged wiring. And make sure of your grounds, even the smaller ones on the body.


I'll check the wire to the distributor in the mornin. I've gone over all the grounds. Replaced a broken one. Just gettin aggravated with the truck at this point.


I checked the wires goin to the distributor. They're all good. I followed the wire harness from front to back of the truck and can't find a bare spot anywhere. If I turn my lights on, 4 ways and a/c the battery goes down to the red and truck will die. I checked all the fuses and relays. I've really got no idea what else to do.


If all the wiring checks then the only conclusion I can draw is the alternator is not turning on, check the dash and make sure that the battery or alt light comes on when you turn the key to on. That light is the exciter for the alternator.


I found 2 different wiring diagrams for your truck, 1 shows just the normal wiring set up, the other shows that the alternator is an ECM controlled alternator, so if yours has an orange wire that goes to the alternator then you have an ECM controlled unit and that maybe your problem, the ECM is not turning on the alternator.


I really appreciate ya tryin to help me out. The only wires goin to the alternator is the one that runs to the battery and a ground wire. The battery light comes on when I turn the key on. There must be somethin I'm missin. I've checked, double checked and rechecked the wires under the dash. Can't find anything. Would my headlight switch be bad?


Have you done a voltage check at the battery with the engine idling and then with the headlight on?


No. I didn't think to check the voltage because I changed the battery and it didn't make a difference. I pulled a battery out of one of my other vehicles and put in it and it did the same thing.


Then it might be a good idea to do so. It should be about 14.2 at idle, then turn the headlights on it should drop to 13.8 and stay there.


Here, take a look at this


My voltmeter's over at the barn somewhere. I hooked up one of my other vehicles to it wit'em both runnin. Didn't make a difference. I'm gonna look under the dash in a bit.

Did u figure it out mines doing it

Please reply! mine is doing the same thing and its driving me nuts trying to figure it out

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