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  #1  
Old November 9th, 2006, 09:14 PM
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Charles Galpin
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Need help diagnosing electrical issue

I have two problems, but I hope one is just a symptom of the other. At MAR my truck developed this "interesting" electical problem that has me stumped. I am pretty sure it's a short somewhere but I'm looking for tips to try track it down. Here are the key data points

1. The running lights stay on even though the lights are off (and even if I remove the light switch). They also stayed on after turning off the ignition when I was last looking into it, so I had to disconnect the battery. Headlights work fine.

2. When I hit the brakes, the guages dip and will kill the engine after a few seconds. This was the original symptom at MAR. I pulled the brake fuse to get home but can't drive it like this.

3. When it's in this state, I lose power to the guages and the dash.

4. Removing bulbs has curious effects on the engine idle speed and the brightness of the other lights (bad ground)?

5. I wired up trailer lights shortly before MAR, but I yanked them first thing when the problem started and it made no difference (nor do I see any signs of shorting at the connecters back there).

I have checked all the bulbs and sockets and they all look good - no signs of shorts. I have no idea if all the bulbs are correct, but I haven't made any recent changes.

Do you have any tips on how to track this one down? I really need to get her running again.

The other problem is my truck is running like crap - barely idles and has no power. It started as I limped home from MAR. Started running poorly with no power and later after washing it the check engine light came one. I had a code 45 (right lambda sensor) which I cleared and hasn't come back, but it barely ran for the few minutes I tried running it. I'm still down hard with the electrical problem.

thanks in advance
charles
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  #2  
Old November 10th, 2006, 12:24 AM
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Sounds like a brake light short somewhere to me.

Also,
there's a thread in Source, where the trailer wire/ connector was corroded and shorted, which affected all kinds of problems with the brake, side, and dash lights. When the brake was depressed, the dash liht came on? The problem was found at the frame rail where the trailer wire set up is.

Another similar symptom problem that was posted, was that the brake bulb, or rear light bulb had internally shorted.

Since you hooked up a trailer, I would start there. Also when bulb connectors corrode, it's very hard to see it, and thorough cleaning or replacement is necessary. A test light or volt meter would help greatly..

Then the ignition switch itself could have grems..

Elect. probs are a PIA.. I'm just guessing..
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  #3  
Old November 10th, 2006, 01:21 AM
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I second Marc. The bullet connectors for the rear lights can corrode and cause all sorts of weird problems. The connectors are behind the passenger side rear speaker box. Clean them and see if it helps. Also you can start diagnosing there by disconnecting the brake lights. That'll tell you if the short (if there is one) is upstream or downstream of the connector.
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  #4  
Old November 25th, 2006, 04:36 PM
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Leaning towards the ignition switch. Any way to prove it?

First, thanks for the input, and here are some additional data points.

1. When I got back to looking at it today, the problem of the running lights staying on with the ignition off went away, and now it's back to just when the vehicle is running.

2. If I just turn the ignition on to the run position, the fuel gauge works and the running lights are off. Once I start the truck, the running lights come on and the fuel gauge stops working (actualy stops as soon as I turn it over).

3. Also the turn signals work with the ignition on, but as soon as the truck is running they stop working too.

4. Turning on the headlights causes the same effect on the engine as braking. the wiring diagram looks pretty damn simple, with only the ignition switch being something that could fail inbetween these two states.

5. There is a dim headlight indicator but no other dash lights when the running lights are on. If I turn on the headlights, the dash lights come on.

6. My manual claims there are 2 grounding straps, one on the driver side of the engine, and one dead center on the firewall. My truck has neither. Anyone have pics of theirs?

So I am wondering if the ignition switch is to blame here. Anyone know how to test for sure?

Quote:
Originally Posted by thewap
Since you hooked up a trailer, I would start there. Also when bulb connectors corrode, it's very hard to see it, and thorough cleaning or replacement is necessary. A test light or volt meter would help greatly..
You're telling me. Mine got wet at MAR and I took it apart to remove the battery and let it dry. Today I put it back together and it's buggered. Will make a run to the parts store shortly

I went through all the connectors again and don't see any issues with the rear brakes - see below.

Quote:
Originally Posted by thewap
Then the ignition switch itself could have grems..

Elect. probs are a PIA.. I'm just guessing..
This is driving me nuts I'd like to try confirm it's the ignition switch before buying one, but thats where I'd put my money right now.

Quote:
Originally Posted by jimngo
I second Marc. The bullet connectors for the rear lights can corrode and cause all sorts of weird problems. The connectors are behind the passenger side rear speaker box. Clean them and see if it helps. Also you can start diagnosing there by disconnecting the brake lights. That'll tell you if the short (if there is one) is upstream or downstream of the connector.
Thanks, this was the kind of prod I needed to start isolating the problem. I disconnected both sides and the problem still occurs. The fact that turning on the headlights kills the engine too make me think it's not isolated to the brake lights at all though.

Thanks again
charles
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  #5  
Old November 25th, 2006, 11:47 PM
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I'd check the wiring around the main lighting relay. If the wiggle test doesn't result in anything then try replacing the relay before buying a new ignition switch.
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  #6  
Old January 1st, 2007, 04:38 PM
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Happy New Year!

Stupid question time... Which is the main lighting relay? I can pull all relays and it keeps running and the running lights stay on too. I can pull al fuses except for the fuel pump as well, and the running lights stay on. According to my manual, the lighting relay is one of the other center ones, and since I only have/had 2 out of 3 relays, that just leaves one, and i haven't been able to get it to run long enought to try turning on the headlights with the relay out. I managed to get it to idle for a bit, but for the most part it takes careful throttle control to just keep it running at 2K+ rpm.

To get it to start I need one relay (rightmost on the center fuse block) so I assume thats the starter relay.

So given the running lights stay on and the problem doesn't go away, I don't think it's a relay issue.

I unmounted the fuse box and everything looks fine back there, no change while wiggling wires.

Anyone know how to "hotwire" it? IE hookup the 4 wires that go to the back of the ignition switch so that it can start and run, but remove the ignition switch from the equation?

charles
p.s. Loic helped me find my ground wires to the center of the firewall. I don't see one on the driver's side of the engine still, but no longer think this is necessarily a grounding issue.
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  #7  
Old January 1st, 2007, 07:57 PM
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When I had some gremlins in my electrical system I found that the serpentine belt tensioner was shot. My radio would turn off if I put my blinker on or my wipers, my alternator would stop working, and random lights would dim. I replaced it and everything corrected.

Just another thought if the brakes and ignition don't pan out.
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  #8  
Old January 1st, 2007, 08:03 PM
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Charles Galpin
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Thanks Mike

I'll double check mine but I think it's fine. I get a steady 13.9V when its running (11.9 when not) so I don't think thats it. Mine isn't really random/intermittant - whatver the hell is wrong is pretty consistant.

Thanks again
charles
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  #9  
Old January 2nd, 2007, 06:00 AM
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My ignition switch broke up internally. gae weird starting/stopping issues.
Basicly in ignition has power going in and this power goes out to ignition and the starter circuit. You could wire the ignition on permanently (for testing or youll burn out the coil) and see if that helps by conecting the terminals together by-passing the ignition swithc ompletely.
Your engine needs an earth strap from the block to the chassis or the return current from the starter & coil won't have anywhere to go.
Earthing problems are a so & so to sort. never assume that an earth is OK because it looks OK. Clean with a wire brush and reassemble with vasaline. same for all the connectors too. I use a small round file to clean all bullit conector females and then pack in some vasaline to keep corrosion at bay.
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  #10  
Old January 3rd, 2007, 01:22 AM
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I am no mechanic but, it sounds to me like you definitely are shorting out somewhere. Check your alternator wires and make sure that it isn't grounding out on the frame under the truck. The alternator has to be part of the problem because when it comes on, all the strange things start happening. If it is sending + to the - frame, it could be making some wierd connections and turning things on and off. Just a thought, good luck.
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  #11  
Old January 3rd, 2007, 02:28 AM
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The ground from the battery to the frame and then to the transfer case needs to be removed and then replaced/reinstalled after cleaning surfaces. Definitely the same with the ground to the firewall. Go crazy with all the connectors-disconnect and spray WD40 or contact cleaner in all you can and pay attention to them for corrosion as you disassemble. Pull apart the Maxi-fuse block and inspect for problems. The fusebox also connects to the starter. Be sure the + connections to the starter are not contacting the ground of the starter or engine block.

Have you got a good circuit diagram to work from?

JP
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  #12  
Old January 3rd, 2007, 08:10 AM
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Charles Galpin
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Thanks guys.

I'll definately do this, hopefully this weekend. I do have wiring diagrams, but I'm obviously not the best at this Everything I have looked at looks fine (to me) though, including the starter, grounds I can find, and the maxi fuse block.

Wouldn't I see sparks or smell burning or something if I had a short this bad?

charles
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  #13  
Old January 3rd, 2007, 02:06 PM
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If one of the feeds to the battery was shorting to ground and was unfused fire would result in my experience(it's happened twice ). The plastic insulation just drips off the affected cable which glows an alarming cherry red followed by lots more smoke comimg out of the rest of the loom.
They put all the smoke in electrical things so you can tell when they're not working properly
If omly a little smoke comes out it might be fixable but if all the smoke comes out at once in large amounts you need a new part. Lucas parts tend to let lots of smoke out suddenly

Follow-up Post:

Just reviewing the whole thread and it struck me that that one offroad site I frequent has electrically conductive (when wet) mud probably due to high iron content. This causes all sorts of interesting electrical problems.... one of my friends rolled his truck, got mud in the ignition swtch and the truck had all sorts of interesting electrical problems for months afterwards.
Don't know What MAR is like but could this be something to look into?
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  #14  
Old January 4th, 2007, 10:14 AM
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MAR is mostly clay. Interesting thing about the mud being conductive though.
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  #15  
Old January 4th, 2007, 12:05 PM
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Mmh, it certainly sounds plausible. It happend after running around in the mud for a few days...

Haven't had time to look at her again, but I do no I have no melting or burning that I can detect

If I don't get this thing running before the weather warms up, I'll have to try do a more thorough cleaning, although I did powerwash it after MAR.

charles
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  #16  
Old January 6th, 2007, 09:22 PM
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Here is an addition to the symptoms:
- when you turn the key on Position I (Accessories?), in place of hearing the fuel pump, you do hear the relay, the running lights turn on, as soon as the relay stops, the running lights turn off.

So it seems like the circuit that is supposed to get power to the fuel pump has something wrong with it.... That would explain why the engine has troubles running properly.
Anyone has any good schema they could share? (this is for a 1994 D90)
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  #17  
Old January 7th, 2007, 07:22 PM
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I think I owe Loic lunch next time he's working from home (which is near my work)

In case it wasn't obvious, Loic came over on Friday night and we spent a few hours looking at this. Yes, disconnecting the fuel pump makes the weird light problem stop. I also wired up a bulb instead of the pump and it lights fine with the weird light problem still gone, so I think this proves the fuel pump (or sending unit) is the cause of the short and not something else in the loom/circuit.

I am unable to disconnect the hose to the evaporation canister so I haven't gotten the tank dropped far enough to pull the pump yet. I intend to take it to a local parts store to visually compare it to the Carter P74006 mentioned here on the forums as a replacement (I'm always up fro saving $200). Anyone have any experience getting the connector apart? In another thread, someone says there is a tool for this.

Thanks again Loic

charles
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  #18  
Old January 7th, 2007, 10:31 PM
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Is this a hose or a connector? It has been a while but I think its just a hose, if so is there enough length to cut it to get the tank out of the way??
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  #19  
Old January 7th, 2007, 11:26 PM
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It's a hose with a connector in the middle

Of course I can cut one side, but it's not long enough to cut without replacing it, and if it's just a matter of knowing how to trigger the disconnect I'd rather just do that.

But that said, it's likely I'll end up cutting it - seems stupid though. lol.


charles
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  #20  
Old January 25th, 2007, 07:41 PM
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Sadly replacing the fuel pump has not solved it. The sad story goes something like this

1. Ponied up for replacing the complete pump assembly as I managed to twist one of the steel pipes coming out of the pump disconnecting the rusting connectors. Got a great deal from George at rovers down south though.
2. After installation, the telltale lighting issues of this problem where still there.
3. I futzed around a bit, not really changing anything, but running it for a while with the battery diconnected, the "problem" went away.
4. I started reconnecting everything bit by bit and eventually hooked up the battery again and still the problem was gone. Even stopped and started it a few times and it was running great.
5. Being foolish enough to think it might be solved I headed out for a test drive (in the snow) and went well until it broke down pulling into a gas station a mile from home. It died while braking, exactly the same problem as before, and the light problem was back.

At that time the fuel pump was not pumping! I got a tow home (btw, don't ever try get your wife to tow you home in the snow uphill..)

At home the light problem was still there, but the I could hear the pump. Right now it won't start, has the same "no fuel" symptoms as before (despite the pump working) so I'll replace the fuel filter once I get a hand pushing the POS into the garage. Too damn cold out there.

Sucks to be me.

charles
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