Loses all electrical power after it's shut off, and it's not the battery cables...

[shadowfax]

How's that for a headline?

'88 MM Sport. The problem is intermittent. Starts just fine the first time I run it for the day. I get it somewhere, shut it down, then 5-10 minutes later come back and turn the key, and nothing. No gauge lights, hazard lights, absolutely no power anywhere. Anywhere from 30 seconds to a few minutes later, it'll start like nothing happened.

It never dies while running, and doesn't always have this problem while restarting.

The battery connections are tight, and I inspected the wiring, nothing burned, cut, or shorted. Battery reads 14v when tested. Unfortunately I don't have an electrical shop manual for it, so there might be something somewhere that I'm not looking at. Also unfortunately it's only done this while away from my garage so I haven't have all my tools to test with, so I can't verify that the battery is putting out 14v at the time of the problem.

Any ideas on what I should start looking for? Thanks all.

[pennyman1]

take the negative battery cable and trace it down to the block, and clean all the places it bolts down to. Also check the condition of the cable itself - if it is green at the terminal end, it can be compromised to the point that when it heats up it no longer connects good enough to allow current to flow.

[NueDemShlak]

Check ground cables. And I don't know a whole lot about these trucks electricals, and it's been forever since I've worked on it, but I remember there being a thing on the driver side fender that had "wire fuses". I don't know what the technical term is, but I had issues with mine and one was broke and would do weird things, been so long ago, can't remember what it was even doing!!! :grinno:

[pennyman1]

those are fusible links - undersized wire that burns out when too much current is drawn on the circuit. 1st gen trucks have them, not so sure about the 2nd gen trucks.

[Raikinx]

My truck cut out on the highway and had absolutely no power or anything. Mine is a second gen and its just as NueDemShlak described. There is a box looking thing on the driver side fender near the firewall and one of the wires had corroded and got disconnected, it caused the power to be cut off to almost everything. Now mine has been rewired and everything so it may be different but its worth taking a look at.

[shadowfax]

Sorry for taking forever to respond. Life got crazy for awhile there.

You guys talking about this thing? Under the blue-capped wire terminal?

17494

If so, I just ran the truck for 10 minutes and that thing is hot as hell. Burned my finger on it. I'm guessing that's not supposed to be like that? Where can I even get one these days?

Thanks again for all the responses.

[pennyman1]

that is the ballast resistor for the ignition coil - it will get hot when the truck is running - that is why it is made of ceramic.

[camoit]

Tell me does the battery have new clamps on it? You know the red and gree ones? If so the powder coat on them is the problem. While they look pretty in the package they will cause a host of problems because the coating is on the sides that are going to touch the post and wires.
Also if the ground wire from the block to the engine is missing then the clutch cable can become the ground. This can be a problem as it can burn the cable.

This is the poster child of problems. Powder coating stops electrical current.
So by looking at this picture you can see how little contact is made where it counts.
17495

[shadowfax]

Nope, posts are old and clean. Battery's in good shape. No corrosion anywhere. Wires look good and pass the tug test all the way down under the truck.

The reason I thought it might be the thing on the fender is that a couple of times I smelled something burning while driving the truck but chalked it up to the crappy vehicles it was near at the time. I get a solid 14+ volts when the truck is running, 12.6 when it's not. That's measured across the terminals, and also with one probe on positive and the other on the transmission cover or the valve cover.

Yesterday I ran it up to temperature, then shut it off and restarted several times to mimic conditions when it died before, but could never get it to fail. I'm starting to have a bad feeling that this is going to be one of those annoying problems that are so intermittent that it's almost impossible to diagnose.

[shadowfax]

(can't edit) if the thing in my pic is not a fusible link / main fuse type thing, *is* there one for my truck that I can start looking for? It's really behaving as though a wire in a fuse/relay that controls all electrical power is momentarily disconnecting due to heat. If it weren't for losing every electrical accessory including the hazard lights I'd think I had a failing key cylinder, but that wouldn't kill *everything* electrical.

[camoit]

When it does fail. Do the lights or other things work? Head lights, parking, hazard, brake dome? Things like that. If they work then it's a key problem If not then it's a cabling problem. Corrosion in the positive or negative, bad fuse panel connection. You need to cray around a test light. Not an LED one. but the old fashion snap-on with a 3 wat lamp in it. It should draw enough to show the problem as you hunt around for it. I have also seen a battery break internally on the post. Some times it would work just fine others nothing would.
Also check the starter for loose or sparking on the poles.

[lush90]

I had a very similar problem with my '91 and it turned out to be a loose connection in the wiring harness under the dash, just in front of the drivers door. I found it by holding the key in start while pushing/pulling different wiring. The white plastic connector had started to melt which was the burning smell. Next time it happens, feel those connectors for heat, then try moving them with the key in start. I ended up cutting the connector out and soldering the wires. You might even see the blackened plastic where the arcing is occurring by giving it a close inspection. Good luck!

[shadowfax]

Yes, everything fails. No electricals in the truck whatsoever.

I'll have a look at the under-dash connector after work. That sounds like it could definitely be it.

The broken battery post is also an interesting idea. I haven't come across that before, but this is the battery that came with the truck, and there was no battery clamp when I bought it, which makes me think maybe the battery bounced around in there before I bought it and put a new clamp on...

[pennyman1]

I have had a few batteries do that, and also drop a cel intermittently. Even had a Optima red short out so bad that when you tried to charge it - acid steam came out of the vent because it got that hot to boil off the gel inside.

[camoit]

Cary a test light and volt meter. When it fails go into test mode and start working your way back from the battery. That's the only way you are going to find the unicorn.

[shadowfax]

Yeah, I've got a multimeter and a test light in the truck now. But, I poked around under the dash this afternoon. That was instructive. First, I pulled the weird-assed wire that some idiot had jammed into a 20A fuse and ran over to what I assume was a radio before the radio disappeared. Then I looked at the 2 white connectors mentioned above, but they both look good.

But! I discovered that for some reason the entire wiring harness appears to be routed up into the steering column via 3 black connectors just to the right of the column. One of those connectors gets pretty hot when the truck is running. Not burning, but warmer than I'd expect. If I disconnect it, all electrical power to the truck dies. So the next time the truck has no power I'm gonna be looking hard at that connector.

I also found a quick-disconnect wire that's grounded to the throttle. It's disconnected at the quick-disconnect -the other side travels across the steering column and over to somewhere in the fuse box area. I'm guessing that is not a stock wire, but if someone could confirm that, it would be great.

Looking under there I'm seeing a lot of evidence of weird custom wiring jobs in its past, so I'm actually kind of surprised the thing's done as well as it has for the couple of years I've had it.