electrical help: running lamps on but no headlamps!

[Phil Stuart]

This morning while driving my 89 to work the headlights just went off for about 15-20 seconds then came back on. They stayed on for a while then about 15 mins. later the exact same thing happened. Then The last and 3rd time it did this the headlamps wouldn't come on at all

The parking lamps stayed on the whole time but the headlights were cutting in and out like it could be a ground wire or a loose connection. This has happened before about two months ago.

Good thing I had the fog lamps on 'cause I wouldn't have been able to see squat!Oh, I tried the high beams and these would not work either when the headlamps cut off. Any advice would be a big help. I'm at work now so I'll check back on this in a bit. Thanks a bunch,



Phil



Another clue, went out to check them about two hours later and they now come on,high beams too, what gives?Is something heating up and then cooling down which affects them?



Phil

 

[Philip]

Pull the headlight switch and see if the wiring plug has burnt up.



This is a common issue on our models of trucks. Most of the time it burns up the marker terminals. But I have seen the headlight terminals come loose on the switches before.

 

[Phil Stuart]

Thanks Philip,



I will do dat!



Did not smell any electrical odor/burnt wiring. I do have a 7 circuit painless wiring block if necessary I'll just tap into one of the empty circuits for just the headlamps (if this is feasible).



Phil



p. s. I will let you know what I find after I pull the switch and check it.

 

[Philip]

Most of the time you won't smell it burning. I have replaced two harness plugs in 7 years. Never smelled anything.



I used to work in a injection molding factory. I know the smell of burning/melting plastic.

 

[john colgan]

I think these are connected to a fusible link if memory serves me correctly.

The links are located right next to the battery. There should be a couple of extra leads from the positive terminal. One is for the heater grid, the other goes to the link. The one for the link goes into a connector, then splits into four separate fusible links. Check those, if this is the problem you can splice a piece of wire in place of the link to keep you going, but you should replace the wire with the correct rated link as you will not have any overload protection without the link. If you need to know the link rating I can look it up in the factory manual when I get home.

John

 

[Tim1]

I posted a fix by using relays on the headlights and tow light circuit. Works great for 3 years now. Tum

 

[Phil Stuart]

Headlight gremlins

Thanks for the tips!



I looked in my 89 FSM yesterday and in the wiring diagram sheet for the headlamp switch it shows an internal 20 amp circuit breaker that is integral with the switch and is fed from the BAT wire and seems to be in series with both high and low beams. I thought this could be the culprit and I believe that it is the original switch @257,000 miles. I also checked the wires coming out of the switch at the block for melting or looseness.



I swapped out the switch with one I took out of my 86 gasser truck and it seems to be OK so far. Drove it into work this morning and everything seems to be working. I noticed that the switch from the 86 has one less terminal (no "P" terminal) but I didn't notice any difference in the lighting.



Phil

 

[CDegner]

I am having the EXACT same issue right now. I hopped in the truck to head home from work at 9pm the other night. Started ehr up and no lights. Running lights on but no headlights. Had to walk home.



Today, I pulled the seitch and it appears the switch is bad. When testing between B1 and H on the switch, I am getting a lot of resistence and even that is intermittent. If I take a length of wire and jumper between the terminals on the connector, I have lights.



Anyone know of a source for these goofy switches?



***EDIT***

I guess I should have read a little further in the search. It looks like NAPA carries this part. Gonna get one tomorrow if so! Oo.



Carl