I recently purchased a 88 pickup, and while cleaning out the glove box I noticed this wire. Does anyone know what this wiring harness is for (it's directly behind the glove box) and/or what is the purpose of the jumper wire? I can pull the dash apart and trace the harness if I have to, was just trying to avoid that.

 

Looks like the PO did some horrible splicing. Do those wires go into the ecm?

 

I have the same truck. I have a crappy old style schematic but It looks like wiring to blower motor. Yellow/red is low speed, blue/red is next then blue/yellow, blue/black is hi speed. White/black is ground.

 

Yep....the radio was the same way, I re-did that and that's when I found this one. The AC isn't working, it's missing several AC lines and I'm still trying to figure out just exactly what the PO did. I'm not sure whey you'd want to connect these, I guess so you just have low/hi instead of low/med/hi.

 

I think that's the connector for the ac relay, which is located right underneath it, I can see it in your pic.

 

It's definitely the blower motor wiring. I disconnected the plug and the blower wouldn't turn on. However, now I'm even more confused. There are 4 speeds. Low doesn't work at all, the 2nd and 3rd are reversed, and high works. I unhooked that jumper wire and now nothing but high works. I can easily hook it back up and forget about it, but was just curious if anyone here had any suggestions on what might be causing this?

 

I would check continuity through all the switch positions. Not sure if your switch has the pins labeled.

Schematic shows 4 speeds and I just checked my truck to make sure.

Pin 1 - 4th speed contact

Pin 2 - hi speed contact

Pin 3 - 2nd speed contact

Pin 4 - ground (pivot point of switch)

Pin 5 - low speed contact

So stick one wire of your meter on pin 4 and the other on each of the other pins and see if you get continuity on each speed.

 

OK, I'm looking at the FSM and here is the test for the switch.

Low speed should have continuity between pins 4 and 5

2nd speed shows between 4, 5 and 3.

3rd speed 4, 5 and 1

Hi speed 4, 5 and 2

Looks like pin 5 on all because it is the yellow/red going to the heater relay.

The blower resister test is to check for continuity between terminals 2 and 4.