This problem arose out of nowhere a few days ago, on an '88 K5 with just the stock lighting. If I turn the high beams on after startup, it'll run fine for about 15 minutes, but then all the lights on the truck will start to shut off and come back on, repeatedly. If I turn the high beam off I'm back to normal with all the lights front and rear and in-cab functioning, but if I switch the high beam on again I get the same problem. It's like I get an overload after a while with the high beams on, and a circuit breaker cuts and restores the power... Does anyone have any ideas on where to start looking? It naturally sucks not being able to use the headlights on dark winter nights.
CK5
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All the lights start to flicker when turning on high beam!
- Thread starter AuH2O
- Start date
plumber mike
1/2 ton status
I had the same problem. Started with just the high beams. When they were on for a little while they would just go out but the parking lights would stay on. It turned out to be the headlight switch.
blazin' j
1/2 ton status
my 86 started doin this 1 nite outta nowhere as well...then 1 day i installin my fog lights and while all my lights were on, they went out again...jus buy a new headlight switch and ur problem should go away...mine did
bodacious
1/2 ton status
Mine is doing the same thing. I though it might be the dimmer switch.
blazin' j
1/2 ton status
btw, headlight switch is like $10 bucks @ autozone, n a pain @ change, very simple, but a pain...gotta find the lil release button on the old switch to pull the knob out b4 u can take the switch off...if u have trouble findin it (release button) on the old 1, look @ the new 1 to find it...thats what i did and it worked for me...no problems with lights after that...
The thing is though, I changed the headlight/dimmer switch just about 6 months ago because the old one was basically worn out; and it's been working flawlessly since. And it's an OEM from Delco, too. It doesn't seem right that it would turn bad after merely half a year. But ok, I'll start with pulling the switch out to inspect it.
Check all your grounds. If all grounds are clean and tight then turn on all electrical items and then check voltage at the back of the alternator with the engine running, it could be that your alternator is becoming weak and can't keep up with a heavy load and needs replacing. Voltage should be anywhere from 13.5-15.5 but closer to 14.7 or so.
Actually, the alternator is also just a few months old. Genuine ACDelco of course. 
88amps or thereabout, which was the biggest housing I could fit without revamping the compartment.
Haven't gotten to checking the switch yet. If that turns out to be good though, then it's on to grounds and wiring...
88amps or thereabout, which was the biggest housing I could fit without revamping the compartment.
Haven't gotten to checking the switch yet. If that turns out to be good though, then it's on to grounds and wiring...
Actually, the alternator is also just a few months old. Genuine ACDelco of course.
88amps or thereabout, which was the biggest housing I could fit without revamping the compartment.
Haven't gotten to checking the switch yet. If that turns out to be good though, then it's on to grounds and wiring...
IIRC on an 88 the alternators were more than 88amp more like 120/140 amp. At any rate, i have a stock 140 amp alternator in my 89. Now, just because the alternator is new doesn't mean that it is exemt from going bad on you. I've installed parts brand new out of the box that were bad.
I can't speak for the gassers (hey, I'm a diesel guy... 
), but my '88 6.2L had a 66 amp alternator mounted from the factory. That was part of a 'cold climate' package however (it was originally sold in Canada), which also featured "Special insulation, Special Heater & Defroster, Engine Block Heater, HD Batteries". I don't know if you got that generator without the cold climate package too, or if you got even one step further down, which would've been 56 amps or thereabout.
Naturally though I wanted to step up from 66 when that old one had run its course, but I found that I couldn't go higher among the OEM Delcos than 88 (it was about 88 anyway, I'd have to look up the receipt to be absolutely sure), or the housing would be too big to fit, and I was in no mood for rearranging stuff. But 88 amp and dual Optimas are plenty, and she starts with a flick of they key every time. And above idle rpms, the new alternator puts out close to 15V, so no problems there.
I'm thinking I could have a ground or wiring problem, but I'm hoping it's the headlight switch, since that would be easiest... I'll check ASAP.
), but my '88 6.2L had a 66 amp alternator mounted from the factory. That was part of a 'cold climate' package however (it was originally sold in Canada), which also featured "Special insulation, Special Heater & Defroster, Engine Block Heater, HD Batteries". I don't know if you got that generator without the cold climate package too, or if you got even one step further down, which would've been 56 amps or thereabout.Naturally though I wanted to step up from 66 when that old one had run its course, but I found that I couldn't go higher among the OEM Delcos than 88 (it was about 88 anyway, I'd have to look up the receipt to be absolutely sure), or the housing would be too big to fit, and I was in no mood for rearranging stuff. But 88 amp and dual Optimas are plenty, and she starts with a flick of they key every time. And above idle rpms, the new alternator puts out close to 15V, so no problems there.
I'm thinking I could have a ground or wiring problem, but I'm hoping it's the headlight switch, since that would be easiest... I'll check ASAP.
Mike D
1/2 ton status
In my opinion, all the headlight switches are made in mexico. In order to prevent replacing the switch again in 6 months I suggest ( I also did this ) wiring the headlight and brite lights to two relays ( close to the lights ). Use heaver guage wires from the battery ( with circuit breakers ) to the lights. When you turn your headlights ( or brites ) on the leadlight switch sees 0.1 amps ( from the relay ) instead of 20 - 30 amps. I done this 7 years ago and the lights and everything works perfectly.
jpdrake
1/2 ton status
ive got the exact same problem in my 88k5 and i did replace the switch 4 or 5 years ago. guess ill try another switch.
Mike, that sounds like a good idea, I might put that on my list of things to do. Funny thing is, it probably wasn't more than 6 months since I last changed the switch, for another reason. It came in an ACDelco box, and I thought that would at least count for something, but Mexico (or China) sounds about right as far as quality went... This time I got a Standard Motor Products replacement part, 'cause that was the only thing on shelf. Will be interesting to see how long it lasts.
jpdrake, yep, definitely try the switch first, is all I can say!
jpdrake, yep, definitely try the switch first, is all I can say!
My understanding is that the headlight switch incorporates a self-resetting breaker. What might be happening is that depending on load (like extra lights if wired that way, or bad wires/connections in general) the breaker is/was tripping. If a new one fixes the problem, I'd expect that the load is borderline what the breakers are designed for.
The relay mod should solve the problem if thats it, and would be interesting to test with a "malfunctioning" head light switch.
