Intermittent lights...

I have a weird problem with my lights. If I run with the top switch in the first right position (i.e. no headlights), everything works great, turn signals, dash lights etc. When I switch it to the far right (turning on the headlights) it will work for a while and then (seemingly randomly) I will lose all of my lights, including headlights, turn signals, dash, etc.

Eventually, they will come back on and it seems to help if I turn the top switch completely off (the straight vertical position) and then back on again. Also, this all happens when I'm running down the road, I haven't tested it sitting still yet.

The 3-way switch is obviously one thing to check, but what other things should I look at? Are there any common problems with the lighting system. When all the lights are on, they all work great. There's no flickering or dimming, they just disappear all of a sudden.

There is a breaker in the 3-lever that will turn off the lights and then once it cools down, turn the back on.

From what you wrote, the brake lights, dash lights, blinker systems and maybe black out lights work fine. That leaves your headlight wiring only to check for the short that is probably there. I would look at the area on the firewall where all the wires go through, at and around the hi-beam switch and then just reach in through the grill and feel the wires at the head lights for something obvious.

Yes, it could just be a bad 3-lever too. Check things out first, fix what you find if you find anything, then if nothing was wrong, put in a "new" 3-lever.

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Originally Posted by Barrman

There is a breaker in the 3-lever that will turn off the lights and then once it cools down, turn the back on.

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Wow, didn't know about that. That sounds exactly like what it's doing. So, if it is overheating, that's most likely a short somewhere, right?

Yes, put your hand on the switch and feel the temp before you turn on the lights. A non contact infrared thermometer is best, but turn them on and if something is shorting out, you will feel the switch get hotter.

I'm thinking a really high resistance connection, or a loose/missing ground may be the culprit, if it takes a bit before the breaker kicks.

Typically if you have a dead-short to ground, the breaker will pop immediately after turning on the circuit, but with most anything else you'll get a sizeable delay until the circuit gets hot enough from the resistance to pop the breaker.

Have a good look at the ground wires where they connect at the headlight buckets on each side. They may be rusty and/or loose.

If it is in fact the circuit breaker opening it will probably be for one of two reasons. A defective circuit breaker or a low resistance circuit causing high curent.

Low resistance (high current) can be caused by a short to ground as pointed out by Barrman and Randy.

There is also the possibility of having 12volt bulbs installed on a 24volt system. If you have a 24volt system and this is the case, it seems like the bulbs should burn out but maybe not. The breaker might be protecting them.

Check the bulbs.

Just a thought.

Good luck

Well, I may have found the problem. I'm testing it as we speak. I looked in through the brush guard behind the lights and found two things:

1) bare wires
2) mouse turds

What is it about those bas***ds that makes them want to eat wires? They were chewed almost completely through. Anyway, I temporarily taped everything up that I could see and am testing it now. If they stay on for more than 5 or 10 minutes, I'd say I have my answer and will have to replace the one wire they chewed. Pretty easy if that's all there is.

Well, crap, they're still doing it. I'm going to have to take the whole thing apart and check all the wires. Is the only access to the headlamps from the front and through the brushguard/radiator area? It doesn't appear that you can get to them from the bottom or back. Do I basically just unscrew them from the front and pull them out?

Yup. Old school tech! Pull the ring off and get them out that way from the front.

BTW, did you check the wiring to the tail lights too? Those come on too when the headlights come on. If they're in the same condition as the front, that could be your culprit. From your post it sounded like you just checked the front. Just a thought....

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Originally Posted by Binford

Yup. Old school tech! Pull the ring off and get them out that way from the front.

BTW, did you check the wiring to the tail lights too? Those come on too when the headlights come on. If they're in the same condition as the front, that could be your culprit. From your post it sounded like you just checked the front. Just a thought....

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Good idea, I will check those, too. Lots of wire to check, but I'm guessing 95% of the problems happen at the ends, either near the lights or near the switches. I hope that's right, anyway.

As Barrman noted earlier, check the wires coming through the firewall too. The harness could be chaffing there. Also at the high-beam switch. Power for the lights goes through all these areas, so all should be looked at if you suspect a short.

One other place I have seen problems on MV lights is when the seals get compromised in the blackouts and allow water intrusion. A light assembly full of water, or a water/mud slurry will make for some nice electrical issues too.

Made some progress tonight. I checked the entire harness for bares and cleaned up anything that looked suspect. The one thing I found was a new blue wire coming from the back of the ignition switch and spliced into one wire of a pair that were taped together under the dash. It looked real ugly, they just wrapped the blue around a bare spot they made in the pair. Anyway, I cleaned all that up and left the blue wire unhooked. The lights stayed on longer than they ever had before and never went out. Yay.

Now, the problem is, it turns out the new blue wire someone had run was spliced into the wire going to the coil, so the truck won't start. Obviously, it needs to be hooked back up, but my question is where is this thing supposed to be hooked up when done right? The two wires that were taped together were the coil wire and the blower motor. They come through the firewall, run behind the steering wheel and then into a big ball of wires. That ball of wires then splits out to the dash lighting and gauges. I can see where the blower motor wire comes out and goes to the blower switch, but I don't see where the original coil wire comes from. Should it be in that big bundle? I suppose, I could separate the two wires and splice it in correctly, kind of like the PO had it before, but I'd like it to be done right, if possible.

Anybody got a pic of the back of their dash? Also, can I even get the dash off? I've got a hard top that's welded in and it looks like the top of the dash hooks up under the windshield so that even after the all the bolts are out you have to lay the windshield down.

Sorry for all the questions and ramblings, but this is one of the last things I need to fix. Thanks!!!

Ok, screw it, I went ahead and spliced into the coil/blower wire pair and put a good butt splice connector in. Everything works great and the lights are staying on. In addition, it feels like it's actually running better. They way the PO had it, there couldn't have been more than 2 or 3 strands of the coil wires connected. Now, with the butt splice connector, it seems like it's running better. Maybe placebo effect, who knows. I'm still not real clear on what was causing the breaker to trip in the switch, but oh well, it seems to be working.