Let's all learn how to debug a GAUGE fuse blown due to a short circuit

[vegas]

I crawled under my truck and saw two sets of wires that might be the factory trailer wiring. One is on the back of the crossmember just forward of the rear axle. The other is on the front of the rear most crossmember. Here are pics. Crossmember just forward of the axle:

On the front of the rear most crossmember:

Which one is the factory trailer wiring?

 

[jonheld]

 

[Kernal]

That's not the trailer harness, it may be about two feet further down in your photo, back side of the lower quarter panel cavity. If you remove the cargo area side panel where the jack is stored and look down you might see it spliced into the factory harness.

IME they're attached (port or dealer installed) to the body harness in the left (or maybe right) quarter panel cavity, then routed out via a plug plug/grommet on the inner aspect of the bottom quarter panel over to the trailer hitch. What often happens is the electrical connector dangling off the hitch gets corrosion internally and causes a short there. A tipoff is if the connector is swollen.

 

[vegas]

I already pulled apart the trailer wiring and that didn’t fix the short circuit.

 

[vegas]

Here’s a view towards the passenger side behind the rear most crossmember.

 

[ppc]

Did you actually remove the converter box. Your photos appear to show only the wiring post converter being removed.

 

[vegas]

I pulled apart all of the plugs in the rear and underneath and it didn’t fix the short circuit.

 

[ppc]

This is the converter that can fail and cause problems:

 

[vegas]

Did you actually remove the converter box. Your photos appear to show only the wiring post converter being removed.

Is the converter box what commonly fails? I’ll disconnect it as well.

 

[vegas]

This is the converter that can fail and cause problems:

View attachment 3002286

Ah, ok. Let me disconnect that.

 

[vegas]

I completely disconnected the box and that didn’t fix it.

 

[vegas]

Just to be certain here is how I’m testing for the short circuit:

That’s the yellow wire side of the fuse. So if that has continuity to ground, there is a short circuit.

For the ground I’m using a bolt near where the fuse block is normally located:

 

[blinkerfluid]

remove the center console / area around the gear shift lever - i have had two occurrences where gauge fuse would pop due bunch of wiring messup in that area -

also try disconnecting the PNP switch and see if that sorts it out

 

[TomH]

What is all off this wiring? That's where I would be looking for a problem.

 

[vegas]

What is all off this wiring? That's where I would be looking for a problem.

View attachment 3004263

Those are two illuminated switches that switch relays to power my two sets of Baja Designs lights on my front bumper. I've checked all of that. No shorts.

 

[vegas]

the PNP switch

The PNP switch?

 

[vegas]

Ok, time for an update. I was able to make some real progress tonight. Remember that I was on a hunt for J1 and J4 since those are the two junctions that all GAUGE circuits pass through. One or both of them should stop the short circuit when pulled apart. First, let's find J1:

I see yellow wires going into a junction. Hello J1. This is straight back behind the fuse panel, way up behind the main bundle of wires. It is in the upper left under the dash, directly over the driver's left foot. I pulled this one apart and the short circuit was still present.

 

[vegas]

So it's not J1. Let's go find J4. I really had to rip the dash apart to get to this one. It is almost impossible to reach.

Hello there, J4. I see yellow wires. This is straight back behind the right side of the instrument cluster, behind the air vent. It's really really hard to get to, let alone pull it apart. With both J1 and J4 pulled apart, the short circuit went away. I reassembled J1 and it was still gone, so I know it is a downstream circuit of J4.

 

[vegas]

Now, diving back into the EWD, let's figure out which circuits are downstream of J4 and which other junctions or connectors are downstream that we can pull apart to figure out which circuit is causing the short. Here's a list of the circuits that are fed by the GAUGE circuit and J4:

AC Pressure SW [J4 -> EA1]
AC Amplifier [J4 -> EA1 -> IG2]
AC System Amplifier [J4 -> J7]
Air Inlet Control Servo Motor [J4 -> J7]
Air Vent Mode Control Servo Motor [J4 -> J7]
Center Diff Lock Control Motor [J4 -> IH1 -> EC1 and J4 -> IH2 -> EC1]
Center Diff Lock Control Relay [J4 -> IF1 -> J2 and J4 -> IH1 -> EC1]
Combo Meter [J4 -> dash gauges]
Cooling Fan Radio and Player [J4 -> J7]
Electronically Controlled Transmission Pattern Select Switch [J4 -> IH1 -> EC1 and J4 -> IH1 -> IH2]
Heater Control Switch and AC Switch [J4 -> switches]
Rear Heater Switch [J4 -> switch -> J7]
Rear Window Defogger Switch [J4 -> IF1 -> J8]
Back-up Light LH/RH [J4 -> IH1 -> BQ1]

These fall into a couple of groups.

The first group is the circuits that go to switches and/or gauges:

Combo Meter [J4 -> dash gauges]
Electronically Controlled Transmission Pattern Select Switch [J4 -> IH1 -> EC1 and J4 -> IH1 -> IH2]
Heater Control Switch and AC Switch [J4 -> switches]
Rear Heater Switch [J4 -> switch -> J7]
Rear Window Defogger Switch [J4 -> IF1 -> J8]

These can be eliminated quickly by making sure J4 is reassembled but then unplug the gauges/switches and see if any fix the short circuit.

The second group is the J7 group:

AC System Amplifier [J4 -> J7]
Air Inlet Control Servo Motor [J4 -> J7]
Air Vent Mode Control Servo Motor [J4 -> J7]
Cooling Fan Radio and Player [J4 -> J7]

The Rear Heater Switch also uses J7 but we already eliminated it in the switch group.

The third group is the IH1 group:

Center Diff Lock Control Motor [J4 -> IH1 -> EC1 and J4 -> IH2 -> EC1]
Center Diff Lock Control Relay [J4 -> IF1 -> J2 and J4 -> IH1 -> EC1]
Back-up Light LH/RH [J4 -> IH1 -> BQ1]

The last group is the EA1 group:

AC Pressure SW [J4 -> EA1]
AC Amplifier [J4 -> EA1 -> IG2]

How am I going to test the last three group assuming it isn't caused by one of the switches? In the EWD each circuit has a pin number associated with it as it passes through J7, IH1, and EA1. I first plan to reassemble J4 and then disconnect J7 to see if the short goes away. Then reassemble J7 and disconnect IH1, and then repeat for EA1. This will narrow it down to the group of circuits. At that point I can test the downstream pins in the offending connector to figure out which circuit is shorted.

I'll probably get all of this done tomorrow and report back with pictures. Right now my truck is in sad shape:

Uff da.

 

[vegas]

BTW, the circuit for the Back-up Light LH/RH [J4 -> IH1 -> BQ1] is the one that also powers the trailer hitch plugs. It is the BQ1 plug that should be disconnected to eliminate a corroded trailer hitch plug or some other source of a short in the exposed wiring. BQ1 is a square connector that is 4 pins tall and 6 pins wide. It can be found inside the left quarter panel.