Hit a bump and NO lights

Hi SS,

86 M1009:

Well, I was on rough terrain and hit a large bump at night. The headlights got extremely bright and within a split second all my lights were out (brake, tail, license plate, blinkers, b/o lights, high beams). Prior to this they all worked fine. I've been going through the wiring, which some parts look as if they've been rewired in the past but appears to be using correct color codes. What I've found is on the fuse box my lights fuse socket is slightly melted and only reads 8 volts. However I've tested the fuse with it in and it has power going through, although no more than 8v. I've also replaced the fuse with a new 30a.

The wiring to the headlights has no power in it at all. So, I'm trying to figure out where, from the fuse, the power goes. Does it go directly into the firewall or up to the switches? Also, from the switches it appears wires go further up near the cluster area which I cannot see from the floor. Ive been looking for bad grounds bit everything within visibility is fine, I've loosened cleaned and retightened what I can see.

Initially when I would try to turn on the lights I would have some flickering in my gauges, they would also flicker when I would toggle the high beams (just ever so slightly) as they would before this incident happened. That made me think that my switch works still and the power to the lights is being diverted somewhere. After some volt reading and shuffling of wires behind the dash the guages no longer had that slight flicker when the switches were toggled.

In any event, I can't figure out why I have no power to the lights and why at the fuse is reading 8 volts. I'm trying to go through the wiring schematics but I'm new at this so I'm currently at a loss.

My battery reads just over 12 volts and I can also get readings of 12 volts on the fuse box in other fuse sockets.

Any suggestions would be appreciated.

You checked the fuse but maybe the fuse isn't making contact after the fuse. If you can remove the fuse and use a pick to bend the fuse holder contacts in a bit along with cleaning them. It might help.

However, that doesn't explain your 8 volts. Or the getting bright just before it went dark description. I think you are going to have to open the -20 manual to the troubleshooting section and follow every single step and test for no lights.

I think your fuse box melted. remove the srew from the back side of the fuse box (on the engine side of fire wall) pull the big plug out and inspect the connection at the big plug. probably got corroded and that eventually burns up the fuse box.

if this is the case you need to start searching for a wiring harness the fuse box is not repairable if it melted

If melted lighting fuse. Remove fuse box as noted and replace the melted circuit with 2 in line fuses. Easy to do and never gave me another problem. The loose fuse has the fuse over heating. I even used circuit breakers on a few units and eliminated the fuse completely. Good Luck.

Cucvrus,
Next time you make this repair for the headlight circuit can you please post a few pictures?.
Thank you.

If you say it got really bright for a second then went out, I wonder if somehow it shorted to 24 volts briefly. I have no idea if its even possible, but that could explain the brief very bright lights. And again, no idea where the power supply wiring for lights could come in contact with 24v, unless its possibly on the firewall near the glow plug resistor or glow plug solenoid. That wire that travels the length could possibly shake around.

sneekyeye said:

If you say it got really bright for a second then went out, I wonder if somehow it shorted to 24 volts briefly. I have no idea if its even possible, but that could explain the brief very bright lights. And again, no idea where the power supply wiring for lights could come in contact with 24v, unless its possibly on the firewall near the glow plug resistor or glow plug solenoid. That wire that travels the length could possibly shake around.

Click to expand...

Its possible. I still don't know why it did that. Originally, right when it happened I thought the lights blew out at the same time bece the fuse didn't blow and they no longer worked.

I'll be taking off the fuse box tonight and investigating further. Would be great if I could get some readings from the wires going into the switches also as I've read the black out switch can sometimes malfunction.

Sounds like the 'jolt' while off-roading broke a circuit (from the generator or battery ) and when open circuit the voltage 'spiked way up?'

If it shorted to 24v, it wouldn't blow the fuse since electrically it would use less current at a higher voltage. The brightness of a car bulb can be increased by upping the voltage, but in your case drastically decreased the useful life span.

Another thing to consider is that the headlight circuit could have already had an issue melting your fuse block prior to this incident. There is or was a post about it. Something about the numerous items on the headlight fuse.
https://www.steelsoldiers.com/showthread.php?87544-CUCV-Headlight-Circuit

there is a 24 volt fuse for the volt meter, it probably melted into the light circuit. check to see if volt meter is working.

So far no luck..

-alternator doesn't work anymore. Checked voltage while running and it was 8v. Pulled battery while running and it died. Red wire to alternator shows 8-10v while engine off. All wires connected to firewall mounted power supply have 12.4v to begin with. Somewhere in between alternator and starting point of wire the voltage decreases.

-Left front blinker worked for a few minutes, though not at full brightness. Then, magically left headlight turned on. I tried highbeam and both shut off. Service light switch would all blinker to turn blinker on and off so at least I know that switch works.

-Pulled fuse box and engine side fuse box plugs out and cleaned with alcohol. They were filthy yet passed continuity test.

-Pulled head light switch, cleaned it, and ran continuity test. It appears the switch works (the headlight did turn on momentarilly).

-the fuse box did melt under the 30a but I was able to bend the socket contacts to hold the fuse. I can get voltage of both sides of the fuse, but still it is at 8v.


From what I can gather, certain circuits get stepped down in voltage but I can't find where. Or why. Is there a relay or fusible link somewhere in between that can do this?

Also, to note I currently have only one battery in. The other went bad months ago. But when charged the single battery will start the truck and it will run off it. I have a manual glow plug switch because some time back the truck wouldn't start or run the plugs. I traced the issue to what I think is that 4x6 circuit board and had a hunch it was malfunctioning. Ran a wire to the relay and used the switch to control it, never had a starting issue since.

Is there something I'm missing or not doing right to find why I have 8 volts on certain circuits.

I think the alternator issue is new because when this all happened I drove the truck 200 miles home, just without lights. So from sitting I assume it went bad within the last year.

Is there a switch in the steering column for the blinker and highbeams. Could that be the issue?

86M1009blazer said:

So far no luck..

-alternator doesn't work anymore. Checked voltage while running and it was 8v. Pulled battery while running and it died. Red wire to alternator shows 8-10v while engine off. All wires connected to firewall mounted power supply have 12.4v to begin with. Somewhere in between alternator and starting point of wire the voltage decreases.

-Left front blinker worked for a few minutes, though not at full brightness. Then, magically left headlight turned on. I tried highbeam and both shut off. Service light switch would all blinker to turn blinker on and off so at least I know that switch works.

-Pulled fuse box and engine side fuse box plugs out and cleaned with alcohol. They were filthy yet passed continuity test.

-Pulled head light switch, cleaned it, and ran continuity test. It appears the switch works (the headlight did turn on momentarilly).

-the fuse box did melt under the 30a but I was able to bend the socket contacts to hold the fuse. I can get voltage of both sides of the fuse, but still it is at 8v.


From what I can gather, certain circuits get stepped down in voltage but I can't find where. Or why. Is there a relay or fusible link somewhere in between that can do this?

Also, to note I currently have only one battery in. The other went bad months ago. But when charged the single battery will start the truck and it will run off it. I have a manual glow plug switch because some time back the truck wouldn't start or run the plugs. I traced the issue to what I think is that 4x6 circuit board and had a hunch it was malfunctioning. Ran a wire to the relay and used the switch to control it, never had a starting issue since.

Is there something I'm missing or not doing right to find why I have 8 volts on certain circuits.

I think the alternator issue is new because when this all happened I drove the truck 200 miles home, just without lights. So from sitting I assume it went bad within the last year.

Is there a switch in the steering column for the blinker and highbeams. Could that be the issue?

Click to expand...

So has the truck been converted to12v ?

Yes

86M1009blazer said:

Yes

Click to expand...

There is a good chance it has something to do with the 12v conversion.

That would have been good information to include in the first post. Do you have this:

http://www.roscommonequipmentcenter.com/nn10.pdf

That is the only literature that might help you since your truck is now in the "experimental wiring system" category.