87 f250 fuse 15 blows when starting the truck

John_piv

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Hey y'all,
Been fighting an electrical problem with my 250 for the better part of a month. I put new injectors in my truck, went to fire it up, and saw smoke pouring from my solenoid. When I had put the glow plug relocator with my Banks kit back in, the two thick brown wires had just barely managed to touch an injector line, causing a short. Didn't see any thing wrong with it until I went to put some more diesel in the truck. Gauges work going into town, filled both tanks, and then the gauges wouldn't work the whole way back. Got home and realized I had blown the number 18 fuse.

Now during my diagnosis, I found some interesting quirks. If you set the key to run without starting it, the gauges work fine. Setting the key to the start position and cranking the truck will immediately blow the fuse. If you start the truck and then add a fuse, the gauge's work fine and the fuse survives.

I have no idea what to look for, electrical work was never my friend. Anybody got any wiring diagrams showing the engine bay and its connection to the fuse block? I found a couple for gassers but they don't seem to intermix. Or on the off chance one of y'all has had something similar happen in the past, what's the best solution? I'm halfway to putting a switched source into the power right before the fuse and switching it off when cranking .

Any help is appreciated,
Thanks and Merry Christmas!
 

franklin2

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Here are some diagrams that should match your truck. The first diagram shows fuse 18, and the second diagram shows what it feeds.

Those wires that shorted out are bundled with many little wires. Something may have melted together out there. If you want to try something, unplug the cluster plugs and then see if the fuse blows. At least that might narrow it down. You can see the fuse 18 wire runs all over the place.
 

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franklin2

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P.S. I see circuit 18, red/yellow wire feeds the low vacuum warning switch out under the hood. Check that wire and see if it's melted somewhere.
 

John_piv

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So I disconnected the eight pin plug that goes on the passenger fender, should disconnect all Glow plug power. Set the key to run position glow plug relay still sounds like it's clicking. Pushing key to start immediately pops the fuse and the truck doesn't even crank.

That makes me think it's somewhere from the female part of that wire back, probably somewhere around the solenoid. Could it be one of the fusible links? And if so is there a good way to test them?
 

John_piv

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UPDATE:
I disconnected a little gray connection that runs in the loom going to the alternator. By the look of it, it controls the tachometer but I'm not 100% sure. Doing that I can start the truck and my fuse remains intact. I don't see anything that looks burnt or frayed. I'll keep y'all in the loop.
 

John_piv

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All right, I'm entirely at a loss. Before pulling the tach wires and starting the car would keep the fuse intact, after replacing the tachometer and it's connector, starting the car with it intact will still blow the fuse.

Where on Earth could the short be at? Any ideas at this point would be appreciated, I'm not seeing, smelling, or hearing anything that would point me in the direction of the short.
 

Nero

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So in lieu of blowing fuses, pull the fuse, and connect a digital multimeter set to ohms to the fuse terminal that goes to the cluster. Put the other lead on a good ground. Your meter should read OL, if you connect the cluster and you have less than 10 ohms, that means you have a short to ground somewhere in your cluster. Short to ground is what blows fuses.
 

John_piv

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So in lieu of blowing fuses, pull the fuse, and connect a digital multimeter set to ohms to the fuse terminal that goes to the cluster. Put the other lead on a good ground. Your meter should read OL, if you connect the cluster and you have less than 10 ohms, that means you have a short to ground somewhere in your cluster. Short to ground is what blows fuses.
Which setting? At 200, I have about 17 on the tester
 

Nero

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If you're using a manual range meter, 200 is fine. Do you only see 17 ohms when the cluster is connected, or disconnected?
 

John_piv

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If you're using a manual range meter, 200 is fine. Do you only see 17 ohms when the cluster is connected, or disconnected?
I pulled the fuse out of the box, and now have the cluster unhooked. I now see zero on 200, and 0.5 on 2K
 

Nero

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Check out the printed circuit board on the cluster then, sounds like there's a short somewhere.
 

John_piv

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Check out the printed circuit board on the cluster then, sounds like there's a short somewhere.
Do you mean the circuits on the back of the cluster? If so what exactly am I looking for, burn marks?
 

Nero

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Yeah burn marks, should be easy to see, but sometimes they can be hard to find if it's just a little arc
 

John_piv

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Nothing jumping out at me, is there some way to test the different pins to see if there's a short somewhere in the circuit board?

By the way, thanks for all the help so far! Electrical work was never my strong suit and I would never have made it this far without help
 

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