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'75 K-5 headlights blink then go out

dontoe

dontoe

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On the way to Murphy, Friday night, after driving about three hours, the headlights (on high-beam) started blinking and then went out. After turning the switch off for a few seconds, they came back on when switched on. They would go out again the same way whenever switched to high. I wiggled a few wires under the dash and noticed the dimmer switch was super hot. Actually melted a hole through the plastic on the top terminal off the three. If the high beams aren't used it preforms as normal. I replaced the dimmer switch but same symptoms appeared.


Problem has never occurred before.
Still happened tonight, high beams on maybe....30 seconds.
The dimmer switch hasn't gotten hot again, though it is slightly warm to the touch on low beams. Never noticed if that is normal before.

Can the circuit breaker go bad?
If not, it's drawing to much amperage I suppose?
Or a bad ground?
Headlights work normally other than the CB kicking out and on.
 
Get a couple of relays and wire it up so that the relays handle the high current. That way your switch, dimmer, etc. will only see a few milliamps of current and the headlights will draw current straight from the battery. As a side benefit, you should also notice that the headlights are brighter. :cool1:
 
HarryH3 said:
Get a couple of relays and wire it up so that the relays handle the high current. That way your switch, dimmer, etc. will only see a few milliamps of current and the headlights will draw current straight from the battery. As a side benefit, you should also notice that the headlights are brighter. :cool1:
Click to expand...

I was thinking of doing just that, one extra reason is the extra brightness of course. Just, the problem only just started and I would like to fix it.
 
I'd go with Harry's suggestion. I've done it to my 75 and it makes a world of difference. All the load to the lights is carried by heavier gauge wiring and is a direct route from the junction block on the firewall to the relays and lights.

If your dimmer is getting hot, it would be an indication of high current draw somewhere in the circuit. If it is only in high beams I would look at the high beam terminals at the bulb sockets and the grounds for each. You might have a bad ground that doesn't effect the lower wattage low beams. Even still, look at the lights when they are on to see if there is a noticble difference in brightness from side to side. This can help narrow it down as the stock wiring (high and low beam) feeds the driver's side headlight and then sends wires out of the driver's side bulb socket to the pass side bulb. Essentially, they are wired in Parallel to each other with separate grounds.

If it was drawing too many amps it should have blown the fuse for the headlights, but on a 30 year old rig who knows if it has the right fuse in there. It may have a bigger amp fuse installed by a PO to "band-aid" the problem.

The stock wiring just sucks. All the power runs from the battery to the fuse block then to the headlamp switch then to the dimmer and finally out to the lights. The system has a horrible voltage drop due to the length of small wire and running it all the way into the cab and back out again. Mine barely got 11.5v to the bulbs with the engine running (with a mid 90's 100+amp alternator). This creates dim lights and it only gets worse when you do have a wiring problem (cut wire, bad ground, ect).

The stock system is simple enough you should be able to trace it and find the problem. But for about $20 you can add the relays in an afternoon. 2 30amp rated relays, 2 30 amp inline fuses, roll of wire, shrink tube and connectors and some solder and you got 14.4v's to the lights and NO load through the switches in the cab.

Still, find the issue before you add the relays because if problem is under the hood you could be popping 30 amp fuses until you do fix it.
 
headlight fuse??

A far as I know GM trucks under 1987 dont have any fuses in the headlight wires--just a curcuit breaker in the headlight switch..I had similar problems with my van,when the dimmer switch harness got gangrene from salt off my shoes..I bought a new dimmer switch,and a new plug for it for about 10 bucks--it never acted up again...I think adding the relays are a good idea though,the stock wiring is a bit inadequate,especialy if you add on more lights than came factory on the truck--the headlight switch is barely able to handle the stock lighting.. :crazy:
 
There may be an overload in the circuit, but it's also possible that the circuit breaker in the headlight switch has just gone flaky. The relay setup will decrease the load on the breaker so much that it will hardly even know that it's turned on.

A bad connection will create more resistance in the circuit, which will decrease the total current draw. The connection itself will get hot because of the voltage drop across it (as you found with the connector on the dimmer switch) but it won't cause a circuit breaker to trip. If you're using lights with higher wattage than stock then that could also cause the breaker to trip. Outside of that, you'd be looking for a chafed postive wire that is just barely touching ground somewhere. If it was shorted hard to ground the breaker would trip instantly. :eek1:
 
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