tachometer not working electrical problem

Hey everyone,

I recently asked a question about diagnosing an e4od/tachometer problem I have been having in my truck, and received many good pieces of advice and ideas, however sadly none of those ideas panned out. I have been digging some more and at this point have torn my dashboard to pieces trying to figure out the electrical problem and have made little progress. Long story short I am following the wire coming out of the load side of the fuse that controls my tachometer to try and find a direct short to ground but am making litte progress. I decided to try and find a wiring diagram but could only find the diagram for the 1991 f250 with a gas motor. If I understand correctly, that diagram shows that the wire coming out of the load side of the fuse that has been blowing (the fuse for the tach) splices somewhere before running into the cluster. Can anyone confirm that this is the case on the 1991 7.3 idi? I am looking for a direct short to ground between that fuse and the cluster, and as far as I can tell the only thing between the fuse and the cluster is the splice that runs to both of the connections into the cluster. I have isolated the load wire as far as I can, but it becomes unreachable before the splice (if that splice is even there).

At this point my truck is in limp mode because my transmission isn't getting information from the tachometer, so it is driveable but I want to get it fixed asap. Any information on the diagram would be greatly appreciated

Unplug the sensor on the IP mounting case and replace the fuse (in that order). Crank and see if fuse blows

I already tried that, but it's not the sensor its a direct short to ground between the fuse and the tach

10 or 12 years ago I had a short to ground in my wiring. I started hunting it down, long story short; one of my Clearance Lights (Top of Cab lights) had failed and it was a short to ground. Has anybody here seen a light bulb fail to a short to ground? Start looking at EVERYTHING!

Maybe Wes will be on soon with a wiring diagram. I just have up to '86

DaveBen said:

10 or 12 years ago I had a short to ground in my wiring. I started hunting it down, long story short; one of my Clearance Lights (Top of Cab lights) had failed and it was a short to ground. Has anybody here seen a light bulb fail to a short to ground? Start looking at EVERYTHING!

Click to expand...

Yes when they do this

That would do it, but mine were normal looking and the two bumps were not touching. Thank You for posting these pictures!

After sleeping on this, I realized that the marker lights have only the one bump so this is not a problem for me.