Tail Lights No Bueno

[pappy]

Well, I thought I had it fixed. Tail lights went out on the way home last night. Messed with it today cuz I really want to get a tree next weekend. So, the diagnosis? It's in the wire harness someplace between the fuse and the taillight connectors, or between the fuse and the front marker lights. I'm pretty sure the harness is disco'd by Toyota, so I'm going to have to find and fix what's there.

Marker lights and taillights were removed to isolate those as the problem.
I have continuity on the harness end of the fuse.
I do not have continuity on the switch side of the fuse, and I have 12 volts.

This sucks. I'm going to cry.

 

[SteveLCetc]

When you say "went out" do you mean an open or are you blowing fuses? You have continuity on the harness end of the fuse? What happens if you give that 12v with a jumper?

I had a problem with those little spade fuses - they say they will work in the big spade fuse receptacles, but they will actually slide *beside* one of the contacts.

 

[pappy]

When you say "went out" do you mean an open or are you blowing fuses? You have continuity on the harness end of the fuse? What happens if you give that 12v with a jumper?

I had a problem with those little spade fuses - they say they will work in the big spade fuse receptacles, but they will actually slide *beside* one of the contacts.

It's instantly blowing fuses, and yes, I'm running the correct size. Since the harness is grounded someplace there is no way I'm going to apply 12v without fused protection.

Update. It's not in the tail light harnesses. I just disconnected those and they test fine. Still have continuity at the fuse block (harness side to ground), and at the front marker lights (across terminals). Problem is pointing to the cowl harness between the fuse block and the front of the truck. It could also be in the instrument cluster. I'll pull that tomorrow to eliminate it.

 

[SteveLCetc]

Well, you don't have continuity then, you have a short, correct? Continuity means from one end of a wire to the other. You have a current path to ground.

All the bulbs are out and you still have a short to ground? That kind of problem is sometimes not too bad if you are willing to spend the pennies on fuses. What have you worked on lately in the vicinity of the wiring runs? Try turning off the dashboard lights at the dimmer switch and see if you still blow a fuse...

 

[pappy]

Well, you don't have continuity then, you have a short, correct? Continuity means from one end of a wire to the other. You have a current path to ground.

Correct, there is a short

All the bulbs are out and you still have a short to ground? That kind of problem is sometimes not too bad if you are willing to spend the pennies on fuses.

Yes, all the bulbs except for those in the instrument cluster are out. It pops too fast. I went through 6 last night just trying to figure it out.

What have you worked on lately in the vicinity of the wiring runs?

Nothing. I've worked in the rear, but no work done on the front.

Try turning off the dashboard lights at the dimmer switch and see if you still blow a fuse...

My first reaction was "great idea" and I started to walk out to the garage ... then I remembered that in order to expose the harness from the combo switch on the steering column I unpluged the dimmer switch. So, I guess the instrument cluster is not the problem. Drat.

Keep the ideas coming.

 

[pappy]

Try turning off the dashboard lights at the dimmer switch and see if you still blow a fuse...

My first reaction was "great idea" and I started to walk out to the garage ... then I remembered that in order to expose the harness from the combo switch on the steering column I unpluged the dimmer switch. So, I guess the instrument cluster is not the problem. Drat.

OK, looking at the wiring diagram (think I'm going to sleep tonight? ) ... the "rheostat" for the dash lights is located between the instrument cluster and the ground, not between the fuse and the cluster. So, the dimmer switch is not the problem, and the cluster could still be the problem.

There are also a few other potential trouble spots ... switches on the center console are lit, the heater controls are lit, and the dash clock dims when the lights are turned on.

I'm still hoping it's the instrument cluster.

 

[SteveLCetc]

If you feel lucky you might blow (dry) air up behind the dash. Could be something just needs to be dislodged...

You might also try a multimeter that reads down to 0.01 ohms. 14 gauge wire has a resistance of 0.03 ohms per 10 feet. That might get you close...

 

[pappy]

Late night. Not the instrument cluster.

Pulled the harness from the passanger side firewall going into the engine compartment. All things considered an easy pull. Needed to remove both batteries, starter relay, fuse block from the fender, the battery isolator, and the skirt in the wheel well. Harness pulled down into the wheel well. Removed the tape from the socket to the firewall. No issues. Reinstalled with loom. Managed to get it all put back, except the batteries, before calling it a night.

Tonight ... the dash stuff behind the radio.