'99 3500 Diesel, no warning until yesterday morning and the batteries were completely dead. Hooked up the charger, got it started. The dash gauge showed it was charging, but the headlights seemed dim.

Last night, put the trickle charger on both batteries (taking turns). This morning the truck spun right over and started fine. Turned on the headlights and the truck shuts off just as if you turned the key. Started it a couple of times with the same result after switching on the lights. (also the heater blower fan would not operate, didn't do this before).

I'm going to replace the batteries tonight. I'd appreciate anyone's comments on possible causes for it to shut off with the lights. One mechanic mentioned I might have a short in one of the lights or trailor plugs. What do you guys think?

SilverDollar

 

Maybe some sort of funky ground? The lights are turned on by completing the ground circuit they have 12v+ fed to them all the time and the switch/es complete the ground path. Does it make any difference whether or not the high beams are on? The high beam ground is through the multifunction switch on the steering column and the regular lights are ground through the headlight switch. Might be worth checking those circuits.

 

I agree with checking grounds and connectors, better check the alt. while you're doin it.

 

It doesn't matter if lights on high or low beam. How do I replace the light switch?

 

Truck runs fine as long as you dont turn on the headlights right, just no blower?

Switch-On my 01 you just remove the dash bezel by pulling it off carefully then it was 2 or 3 screws holding the switch in and a plug. Cant remember if the plug has a screw in it or not. One of the switches has a screw holding the plug in. The headlight switch isnt the cheapest thing I think my local napa was in the $80 range.

You might check all of your grounds in the engine area, under the dash area as well as under the bed of the truck I think there is one or two back there.

The heater blower not working I dont think that is connected in anyway to the light circuit but it may be somehow or other. So it may be unrelated and coincidence or it may not be the light switch at all but something entirely different.

I would check the trailer plug at least for obvious things such as nothing jammed in the receptacle, bad looking wires going into it etc

When your truck shuts off after you turn the lights on do the lights stay on?

You might try unplugging the headlights from the connector at the light itself. Start her up turn on the lights and see what happens. That at least would eliminate the headlight assemblies themselves.

Pull the headlight fuses and turn on the lights see what happens. I am unfamiliar with whether or not there are any other wire connectors/plugs between the headlights and the switch but see if there are and unplug them one at time and see what happens.

To be honest if it is not the switch or a bad ground or an obvious short it is over my head electrically. I am mentally challenged in that area.

 

I'd say its a battery issue, turning the lights on steals all the power shutting down the truck.
Best to load test the batterys first.
Then test to see if the truck is actually charging.
Confirm and clean all battery connections and grounds

 

i have the same exact problem, did you ever find a solution?