M1008 tail lights short

[TedO]

Hello, I have a M1008 and my running lights on the tail lights are out. Also all of the dash lights are out, but headlights, brake lights, turn signals still work. The fuse for the running lights, #16 on the diagram, a 20 amp fuse, blows as soon as I flip the blackout switch, even with the tail lights (head lights) off. I disconnected the rear harness from the harness that connects to the fuse box and runs along the frame, so all the tail lights are disconnected, and it still blows the fuse.

Next I wanted to disconnect the harness that runs back along the frame from the fuse box so I could test that for a short. The manual isnt very clear on this. It says there is a bolt holding the harness plug into the back of the fuse box?? I dont see it. I dont want to pull on it too hard, but it seems like there is something holding the plug into the back of the fuse box. How do I get this out??? Also, what is that red wire for?

What else should I look at? Is there something obvious I am missing? Also, I dont seem to be getting the switchable 12v from the fuse box any more. I used to have a tach and a cig lighter hooked into there, and it could be turned off and on with the black out toggle. Should I be looking at something with the black out toggle?

 

[cucvrus]

Under the hood disconnect the batteries and remove the bolt in the center of the bulk head wire connection. It is a 10 MM M6 bolt. The red wire runs to the 12 volt power point at the side of the master cylinder. I am relying on memory right now. But the bolt is a long bolt so it will also help push the 2 bulkhead connections apart as you loosen it. Under the dash you need a 8 mm socket to remove the fuse block from the firewall. Check it all out. You need a short finder. Or a power probe. that way you can work without removing all the wiring harness. But it works either way. good luck. Post a few pictures and the results of your findings. My guess is going to be the rear tail lamp harness is worn thru at the steel reinforcement on the fire wall. The reinforcement is the part that the hydra boost is attached to. That small end wiring harness is the tail lamp harness and that is loose by itself after you remove the under hood bulk head main wiring connection. Good Luck. Post back.

 

[TedO]

Under the hood disconnect the batteries and remove the bolt in the center of the bulk head wire connection. It is a 10 MM M6 bolt. The red wire runs to the 12 volt power point at the side of the master cylinder. I am relying on memory right now. But

Thanks. I wasnt looking at the center of the rear of the fuse box under the hood. I will look closer. I did see the 2 bolts from the cab, but didnt realize those need to come out too. Once I get the cable off and disconnected at both ends, I will check from each terminal to ground using the continuity detector on my multimeter, and a positive signal means short, correct? Thank you very much. I never would have found that bolt using the manual.

 

[TedO]

How do I access the spot where the wire rubs? From the bottom?

 

[cucvrus]

That wiring harness that runs back to the rear is a small branch off separate harness. You will need to un-clip it from the frame as it goes back. they are metal spring loaded P clamps on the frame and plastic ones that the wiring just sets in. You should be able to remove the entire harness that runs back if you wish. i would think you could trace it and visually see the damage to the harness. I imagine it was pinched or pulled and you will be able to repair it in place. Good Luck. Post pictures if you have time to do so.

 

[TedO]

That wiring harness that runs back to the rear is a small branch off separate harness. You will need to un-clip it from the frame as it goes back. they are metal spring loaded P clamps on the frame and plastic ones that the wiring just sets in. You should be able to remove the entire harness that runs back if you wish. i would think you could trace it and visually see the damage to the harness. I imagine it was pinched or pulled and you will be able to repair it in place. Good Luck. Post pictures if you have time to do so.

got it. thanks. I found a replacement on ebay for $15, just in case. I will post pics as I dig into it.

 

[TedO]

That wiring harness that runs back to the rear is a small branch off separate harness. You will need to un-clip it from the frame as it goes back. they are metal spring loaded P clamps on the frame and plastic ones that the wiring just sets in. You should be able to remove the entire harness that runs back if you wish. i would think you could trace it and visually see the damage to the harness. I imagine it was pinched or pulled and you will be able to repair it in place. Good Luck. Post pictures if you have time to do so.

I disconnected the harness at both ends, check for short to ground-nothing. left harness unplugged and put the fusebox back together- it is still blowing fuses. So the short has nothing to do with the rear tailights or wiring harness. Any insight on the second best place to check?

 

[cucvrus]

Hard to say. You may need a short finder. It s a circuit that you put in the fuse holder and it cycles rapidly and you go along and check the suspected wiring. It will beep and light in the area the short is. Other then doing a complete visual check of the wiring I would go around and disconnect bulbs and unplug things to zone in on the shorted wiring.

 

[TedO]

Hard to say. You may need a short finder. It s a circuit that you put in the fuse holder and it cycles rapidly and you go along and check the suspected wiring. It will beep and light in the area the short is. Other then doing a complete visual check of the wiring I would go around and disconnect bulbs and unplug things to zone in on the shorted wiring.

Thanks. I will get the short finder. I was going to go into the dash panel and look at the connection and wiring of the bubs, since a couple dash lights are in the same circuit.

 

[cucvrus]

Unplug the dash panel/instrument cluster. That will eliminate them bulbs. The park/head lights will still work if the short is in the cluster. But I would be looking up front in the light wiring under the hood. Even pulling all the bulbs and checking for the short. The sockets on these trucks are bad for causing trouble. a pinched wire or a rubbed through wire is a definite possibility. Check over on the left fender where the inner fenders bolt fast. I seen one with that wire pinched from the factory and never shorted but the wiring was crushed. Basically you will need to tear into it. California to Pennsylvania is a bit of a trip. But if you want to you could stop by and we could check it out.

 

[TedO]

Unplug the dash panel/instrument cluster. That will eliminate them bulbs. The park/head lights will still work if the short is in the cluster. But I would be looking up front in the light wiring under the hood. Even pulling all the bulbs and checking for the short. The sockets on these trucks are bad for causing trouble. a pinched wire or a rubbed through wire is a definite possibility. Check over on the left fender where the inner fenders bolt fast. I seen one with that wire pinched from the factory and never shorted but the wiring was crushed. Basically you will need to tear into it. California to Pennsylvania is a bit of a trip. But if you want to you could stop by and we could check it out.

I used to live in southwest PA. Wouldnt mind going back.

Is the plug to disconnect the dash panel hanging down by the steering column under the dash? It has a clasp on each end which I popped off, but still cant get the 2 pieces of the plug apart.



I found this plug hanging down from the wiring harness in the rear of the fuse box under the hood. Anybody know what it is?

 

[cucvrus]

I think it is a wire to use in the rear heater on the arctic kit. That should not be your problem.

 

[cucvrus]

The plug to disconnect the instrument cluster is on the back of the cluster. Reach up it is on the outer side towards the door. It runs north and south and you squeeze the end tabs on the plug and gently pull it out. I doubt that is your problem. But it is worth a try. I am thinking chaffed wiring up front on the harness if yoiu have checked the rear harness completely. You need to get a power probe tester or a short finder to go over that harness.

 

[TedO]

The plug to disconnect the instrument cluster is on the back of the cluster. Reach up it is on the outer side towards the door. It runs north and south and you squeeze the end tabs on the plug and gently pull it out. I doubt that is your problem. But it is worth a try. I am thinking chaffed wiring up front on the harness if yoiu have checked the rear harness completely. You need to get a power probe tester or a short finder to go over that harness.

Thanks. I ordered the short finder, and I am going to work on the front harness. I was thinking that the front harness was on a different circuit, but I see now that they both come in to the same circuit.

 

[cucvrus]

Yes but it has a different harness at the bulkhead connector under the hood. Check it out closely. also the power probe helps find shorts easily. i hope that helps you out.

 

[TedO]

yes, it does. Thanks.

 

[TedO]

short

Yes but it has a different harness at the bulkhead connector under the hood. Check it out closely. also the power probe helps find shorts easily. i hope that helps you out.

Unplugged both harness running to tailights and harness running to head lights. Still have the short. Running outof options. Next I will dig into the dash.

Got a short finder, but it didnt help me much. I couldnt make any sense of of the signals it was giving me.

 

[TedO]

Unplugged both harness running to tailights and harness running to head lights. Still have the short. Running outof options. Next I will dig into the dash.

Got a short finder, but it didnt help me much. I couldnt make any sense of of the signals it was giving me.

FOUND THE SHORT. *&@#%!^&**CHEAP CRAP CIGARETTE LIGHTER*&^*%$#@@

My M1008 has a cheap cigarette lighter that somebody plumbed in using the 12 v wires from the courtesy lamp under the middle of the dash. I was using this to charge my cell phone since I bought the vehicle (2.5 years). These cheap lighters cant handle that much abuse. Something shorts out on them all the sudden and you dont know what the cause of the short is. Nothing looks obviously broken or shorted. Since my running lights andeverything else 12 V went out, I naturally started with the most tedious stuff-the wiring harnesses front and back, and plugs into the fuse box. Spent a month on this, working a bit at a time. Stopped by a cop once for no tail lights, as I was trying to get home before sundown.


Now for the real project-hooking up a ham radio through an auxiliary battery/charging system/power junction box-with enough outlets for radio/antenna tuner-rotater/ amp/computer/gps/with enough lights to light up the world, all with a deep cycle marine battery(s).


But first.....need to change out that old radiator and replace the

 

[MarcusOReallyus]

My M1008 has a cheap cigarette lighter that somebody plumbed in using the 12 v wires from the courtesy lamp under the middle of the dash.

That's a really stupid idea from the get-go. "Grab 12v anywhere you can and attach your stuff!" is a great way to generate lots of problems.


If you need advice when you start your ham radio project, start a thread on that here, if you want to. There are several of us that can advise you on that kind of work.

These cheap lighters cant handle that much abuse. Something shorts out on them all the sudden

Yep. Those things are notorious for flaking out and causing problems. If you want a good one, try the marine supply stores. Anything by Blue Sea Systems is quality stuff.

By the way, it's "all of a sudden", not "all the sudden".

 

[cucvrus]

All of a sudden or all of the sudden

The official phrase approved by dictionaries is all of a sudden. The phrase dates back to Shakespeare in The Taming of the Shrew, though oddly the variant all of the sudden was in print six years before Shakespeare.

But we still all knew what you meant.