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Truck dies when I turn on my headlights!

Discussion in 'GM Electrical Tech' started by Big6ft6, Dec 15, 2009.

  1. Big6ft6

    Big6ft6 Rockstar 100 Posts

    I have a crazy problem that just started out of nowhere.

    Here are the symptoms. 1989 surburban. New engine, trans, radiator, thermostat, waterpump etc...all new.

    1) Last night when I turn on the headlights, the truck died...like shutting off a light switch. No CEL illuminated, nothing. Radio and heater fan still work, but headlights and CEl and other lights are dark.

    2) When this is happening I can still start the truck as long as I keep the headlights off, but it seems to start hard and if it is cold I need to keep my foot on the gas to keep it going (TBI engine). Eventually I tried turning on the headlights..no problem...seems to have fixed itself.

    3) Another symptom possibly related or not. My coolant temperature gauge does weird things. Goes all the way to 230, then back down to 210, then to 180, then to 210 for a while, then to 180, then slowly climbs back up to 230. Could this be caused by an electrical issue?

    4) I also notice sometimes I seem to lose my charging system, almost an audible "click" and my voltmeter drops to 12, headlights go dim etc...then a few blocks later..."click" everything brightens back up and I'm back at 13.2 V?? This does seem to be only when my headlights are on....I think...but I'm not sure.


    Any ideas??
    Last edited: Dec 15, 2009
  2. Duncan_Z71

    Duncan_Z71 Rockstar

    is all your battery cables good and tight. i left school yestarday and my truck was cutting off going down the road when i let off the gas. becasue the battery cables were loose. i tighten them up and made sure they were saying in. and it cranked right up and ran fine.
  3. Big6ft6

    Big6ft6 Rockstar 100 Posts

    Hi Duncan, yes the battery cables were tight at least at the battery. That is a good idea though I'll double check all those connections. Possibly a loose/weak ground somewhere.

    When I got home last night I couldn't re-create the problem by turning on the headlights, but if I turned the blower fan all the way up...and then twisted the headlight dimmer switch to activie the inteior dome light the CEL would come on and the engine would start to stumble...WHAT THE??? Isn't that crazy??

    I'm praying that this is a faulty headlight switch....please god make it that simple.
  4. KMKsilverado

    KMKsilverado New Member

    Sounds like a bad ground from the motor to the body and or the computer ground which should be the same but just like anything start basic and work your way up eliminate possibilities.
  5. KMKsilverado

    KMKsilverado New Member

    As for the heat wen the gauge fluctuates does ur heat seem diff, like does it colder and warmer as it moves. If it does you need to purge ur cooling system and or a bad thermo, if it doesnt than the bad ground from motor sounds probable. Also you said the voltage too so get a load tester on the battery while its running put a load on it and see how the truck and gauges react.
  6. Duncan_Z71

    Duncan_Z71 Rockstar

    I have no clue what it could be.
    Could be a bad ground. But theres really no telling.
    I would get somebody who works in all that and somebody you trust to help you out,

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