electrical problems CUCV

[tnbuilder]

I have a 1984 M1009 CUCV with an interesting problem: all my running lights will cut off 2-30 minutes after truck starts. I suspect the problem involves a fusable link in the wiring harness. Does anyone have any suggestions or a complete wiring diagram? All help is greatly appreciated.
Tnbuilder

 

[dstang97]

i think you have a bad switch my old ford did the same thing...scary at night...

 

[tnbuilder]

My mechanic replaced the standard pullout light switch already. It seems to be a problem that appears to be related to resistance (heat buil up), time, or a loose connection. I am leaning away from the loose connection as the lights always work at startup, but shut off down the road.
Tnbuilder

 

[Recovry4x4]

Same problems. Used a flashlight to navigate the GA Rally one night. Problem was the headlight fuse holder wasn't tight enough on the fuse and some corrosion on the fuse from humidity.

 

[tnbuilder]

Thanks for the insights. I'll have my mechanic check the fuse connections. By-the-by: are you a navy man, Admiral?
tnbuilder

 

[Recovry4x4]

Son of a Navy man, husband of an Airman. Have a certain attraction to Seabee's trucks and equipment.

 

[chevyrac66]

I have the same problem on one I'm working on... Loose fuse on the fuse holder... Also the blinker fuse is doing the same thing... Its a pain tracking it down and figuring it all out. Also check the main connectors at your headlamps as I've seen those build up corrosion and cut in and out. Good Luck!

 

[cjkeeliii]

Ditto for chevyrac66's comment. Dielectric grease helps too.

 

[tnbuilder]

Thanks for the headsup on the electrical problem. Turns out that it was the circuit breaker below the headlight fuse, above the blinker relay, which might indicate a chafed wire building up heat/resistance somewhere. We got it fixed, but I may be looking for a complete NOS military wiring harness at some point, so if anyone has a lead on that holler at me. I'm wanting to set up the truck for a serious road trip (Baja for a month next winter, and then the Pan American highway in several years.) Thanks again. tnbuilder

 

[badassissimo]

DId you find a wiring harness? I'm looking for one myself...

 

[pbrstreetgang]

Flashing Headlights

My head lights are doing something similar. After the truck has been running for 20 or so minutes the lights will begin flashing.

No sequence, just random flashing. I have pulled, checked, brushed, and applied diaelectric grease to every ground terminal I can find.

I pulled apart the whole fuse block last weekend, checked the terminals, replaced the fuses, and put grease on all of it.

I even took a small screw driver and bent the terminals up a bit to "grab" the fuses better.

Lights still flashing

 

[Barrman]

Check the connectors on the back of your black out light switches and then move onto the master head light switch if you have checked everything else.

One question, is it just the head lights flashing or all the lights?

 

[pbrstreetgang]

I have already replaced the "master" head light switch to a new one.

It is just the head lights flashing. The high beam lights on the speedometer flash on and off when the lights are on high beam. That tells me that the power is being cut in and out - off and on somewhere, but only to the head lights.

 

[Barrman]

That means your high beam switch is probably the problem.

 

[davidkroberts]

ditto, i would check the highbeam switch if i remember the wiring diagram thats the only place where they would be connected to cause the problem.

 

[3dubs]

Check the Black Out switches. Just bypass them and see if it stops. Always start simple and easy then move on to other things.

 

[SCC2560]

I’m having the same problem with the headlights flashing. Just the headlights. Replaced the headlight switch and dimmer switch, cleaned the headlight terminals and fixed a couple chaffed wires. Still no luck. Wondering if anyone came up with a solution to this one. I’m running out of ideas. Thanks.

 

[Barrman]

Did you remove the ground wire bolts between the radiator and the fender on both sides and clean all of that real well?

If you switches are all good, your dimmer is good, your lights themselves are good and your grounds are good. Then the firewall plug or a rubbed raw wire is your issue somewhere under the dash.

To check the firewall plug use a 10 mm socket and unbolt it from the engine side. There is some kind of really nasty, sticky black goo GM applied years ago in there so either wear gloves or be careful. Us a fingernail file to clean all the contacts on both sides and put it back together being careful not to bend over a pin or two.

After writing all of that. I would suggest if nothing else works that you hotwire the lights. If they shine steady, then hot wire a light by back probing the plug at the light. If all is good keep moving backward until you find a section of wiring or switches that cause the issue.

 

[SCC2560]

Thanks for the info. It’s definitely a little gremlin somewhere. I pulled the big plug on the firewall and cleaned it up. Checked the two grounds by the lights. Even checked the fuses and contacts. Still nothing.
Started chasing it down the wire. Found good clean power up to the headlight (orange/Black wire). But the power out from the switch (yellow wire) to the dimmer switch was inconsistent.
weird that I would have the same problem with two different switches. Checked the contacts and they look good. Put a third switch in and has been on for a good five minutes so far. I’ll let you know if that was the case. Thanks for the help.

 

[SCC2560]

So here's my up date... Hopefully anyone else who has this problem might find this thread helpful....

So conclusion so far is that it was the Headlight Switch...
Apparently headlight switches from O'Reilly's are not the most reliable... I ended up using a headlight switch from my old 72 C10. Better contacts inside? I don't know.. But after five minutes of driving with the headlights on they would start flashing. No pattern of any sort, just start having a party all of their own... I would drive to work at dawn sometimes when it was light out enough that I couldn't totally notice my headlights were on or not and people in front of me would pull over... Thought that was a bit weird after the third guy did it... Pulled up to my shop and noticed the disco going on!

Starting at the headlight itself. found a few dirty connections and some bad patches in the wiring, Cleaned those up. Still flashing.
Pulled the bulkhead off the firewall and cleaned all the contacts. Still flashing.
Changed the Dimmer switch and the headlight switch. Still flashing.
So I got a test light that could pierce the wire to test it. Started at the wire that feeds 12v to the Blackout switch. (Solid Orange in, Orange w/ black stripe out 12ga.) Nice and solid... Then Followed the Orange w/black stripe wire to the headlight switch (poll #1 Batt Feed) Good and solid to the switch. Then the Yellow wire (14ga. ) from the Headlight switch to the dimmer switch, That's where it starts flashing. Put in another switch ( switch #3) and left it running for 45 min. No problem. Also found in the Unit Maintenance Manual pages F-15, F-16 "Unit lighting circuit" really helped.

I'm guessing that the load from the headlights gets too hot for the contacts inside the switch and starts the disco show... Maybe these new switches are not build quite and strong as the old stuff.... Also possible I have some frayed wires down the trail somewhere creating resistance that still need to be dealt with. If anything changes I will post my findings...

Thank you to everyone on S.S. for all the help and insight.