Turn lights on, truck dies?

[Bonshee1971]

Anyone ever had this happen to them? I have a 91 K5 with a tbi 350. I went out to start it and let it warm up before I left the house. It started fine. I turned the lights on and it dies right a way. No spitter or sputter. Then it didnt want to start again. I let it sit a few minutes and it fired right back up. I turned the lights on again and it died again. Any suggestions?

 

[82Scottsdale]

Yea i know a buddy that has the same problem but doesnt have the time to chase it down, and would be nice to find out for him, any idea's?

 

[bp71k5]

Sounds like a short in the headlight circuit.

 

[Desert Rat]

Just a guess but if the alternator wasn't working, then the engine would be running off of the battery alone. Turn on the lights, and the battery can't power both the engine and the lights at the same time. This would only work for a while though. Eventually the battery drains out and the whole thing won't run so that might not be it. Could be a short somewhere too.

 

[dremu]

Well, get thee to a parts store that does free testing of alternators and batteries.

Also check the connections AT the battery for gunk. A toothbrush and baking soda in water will do wonders.

You should prolly check the battery cable at both ends, but my experience is that they get bad at the battery end first.

-- A

 

[blazin_blazer]

or bad alternator....battery has enuff juice to crank once....turn on lights not enuff juice for ignition anymore....then won't start...he lets it sit battery builds enuff to start again.

when u try 2 restart after lites kill it..does it spin over as usual or act like low battery?

*edit...i'm 2 slo, but yea what they said, get alt & bat checked

 

[3/4 Ton Blazer]

Make sure you have a solid coinnection between battery positive and the alternator charging post. When I bought my current K5, I had that same problem, and that line was disconnected, and it would still work most of the time (My alternator was charging by backfeeding another, smaller circuit). I finally found out that that line was bad, and made a new connection from the battery to the alternator, and all has been fine since.

 

[Bonshee1971]

or bad alternator....battery has enuff juice to crank once....turn on lights not enuff juice for ignition anymore....then won't start...he lets it sit battery builds enuff to start again.

when u try 2 restart after lites kill it..does it spin over as usual or act like low battery?

*edit...i'm 2 slo, but yea what they said, get alt & bat checked

Yeah, after it dies when you turn the lights on, it cranks fine. Doesnt act like it has no charge. Then it has to set for about a minute before it will start again.

I think I might take your guys suggestions and take it to my local Auto Zone and get the alternator tested after I do all the wiring checks myself.

 

[dyeager535]

Very odd. Doesn't sound like a battery issue, (shouldn't crank ok if it was) but won't hurt to test. Simple test for this would be to make sure ALL accessories are off, start the truck, then turn your heater on high. That likely draws as much if not more than your headlights. If it doesn't die, it's not an alternator/battery issue. Wiring perhaps, but not the components.

The headlight switch has a self-resetting circuit breaker in there, but that in no way should be tied to ignition, and if it was somehow, all those circuits should be protected individually (fuses or fusible links) and those all are typically "hard failures" where they no longer work once popped.

Fusible links I've actually seen be intermittent, but pretty rare, and your issue is too repeatable for that I'd think.

 

[Bonshee1971]

The heater doesnt seem to affect it. Thats what I was doing when I noticed the problem. I was warming it up to melt off the ice. Heat worked great and didnt cause any noticeable problems. This all just started out of the blue. What you said about the circuit breaker in the headlight switch makes sense but you're right, it shouldnt be tied into the ignition. And from what I see about the rest of the Blazer, I dont think anything has been altered. Its almost completely stock. The only addition that I can see that was done was it had some kind of light bar or series of lights on the roof as it was commissioned as a fire dept. vehicle. But the lights were long gone before I got ahold of it.

 

[Desert Rat]

If it was a former public safety vehicle, then they may have added some extra gizmos to the wirng system. Lots of police patrol cars have battery protectors, or other custom wiring to keep the battery from dying when a patrol car is parked with it's emergency lights on. At a minimum, they usually add extra fuses and other connectors to facilitate the extra lighting, radios, etc.

 

[Bonshee1971]

I brought it into work to do some checking. I found that the left most portion of the fuse panel loses power when you turn on the headlights. There are three fuses in this section: courtesy lights(not working), horn(not working), and an ecm fuse(not working). I would be able to let it set a few minutes after this happened the first time and it would start back up, not it wont start at all. I am kind of leaning toward an ignition switch. It seems like maybe that quadrant of the fuse panel is not getting power and when it does get power, turning on the headlights might overload it and kill it. Dunno, just a guess. I did check all the wiring under the dash and nothing looks butchered.

 

[dyeager535]

I don't see this being highly probable, but perhaps your ignition switch is just out of adjustment?

It could go bad, but there isn't much to them. Heck, you can even pull it apart yourself if you want to find out.