99 Ranger fuse 25 keeps popping

[Bric.wall1]

Hello all,
I just bought a 1999 Ranger XLT with an automatic and the 3.0, and I am in the middle of trying to diagnose why fuse number 25 keeps popping. I have unplugged the radio, instrument cluster, and the GEM module, yet the fuse still blows. I checked the current draw through the empty fuse slot and was getting a reading of about 4.5A which should not blow a 7.5A fuse. The previous owner said the battery was overcharging and then he parked it. Is there something I am missing or could the wiring harness be the problem? This is my first time working on a Ranger and I do not really know how everything works.

 

[Brain75]

Take the fuse out, figure out which is the upstream (always hot) and which is the downstream (fused) side, then measure resistance to ground on the fused side with an ohm meter. Do NOT do that to the hot side, you will ruin your meter... I bet you get no resistance indicating a short to ground.

 

[Bric.wall1]

There is definitely a short to ground, finding out where it is is the problem. I looked for a wiring diagram but could not find the right one.

 

[Brain75]

I don't own a 98-03, so am going entirely off stuff online, but this site:

Fuse Box Diagram Ford Ranger (1998-2003)

Fuse box diagram (location and assignment of electrical fuses and relays) for Ford Ranger (1998, 1999, 2000, 2001, 2002, 2003).

fuse-box.info

says that 25 is:
1998-1999: Generic Electronic Module (GEM), Instrument Cluster
So I see why you went after the GEM and Instrument, but the radio (unless an aftermarket just spliced in any ole place) shouldn't be involved... of those the instrument cluster is the biggest PITA to remove and the most likely culprit.. I'd probably start by tracing the wiring back from the GEM looking for abrasion or some splice from a previous owner, then reluctantly go after the cluster. With 25 out does your radio not work? Is it aftermarket?

 

[Bric.wall1]

I had to take the radio out to get to the GEM module, and I just left it unplugged.

 

[Bric.wall1]

I have singled out the cluster being the problem and narrowed the fuse popping to when the GEM has both the bottom connector and the 26 pin connector plugged in. If I unplug either of the connectors the short to ground goes away. Is there a wiring diagram that will show me which pins should be shorted to ground and which shouldn’t so I can determine if the problem is the GEM itself or if it is something else?

 

[Brain75]

pin 26 (as well as the metal case of the head connector) should go to ground:

 

[Bric.wall1]

In addition to the ground pins, I found that pin 21 for signal return also went to ground. I will keep tracing that when I can get back to the truck on Monday.