1987 Grand Wagoneer dead gauges issue solved

[TimGee]

Hey all,

So the cables on the car battery were reversed last week and it killed the truck. I brought it to the mechanics and they got it back up and running but I discovered on the way home that the fuel, battery and temp gauges were all non responsive as well as the clock was dead. It ended up being a fuse.

Here's the fuse block:

Fuse Block2.jpg

Here's the closet diagram I could find (1989 Block)

1989 GW Fuse Block2.jpg

The blown fuse was the 15 Amp on the right/center "IGN/LPS"

Replacing that fuse resulted in all of the gauges working which made my morning.

Guages2.jpg

BUT I noticed that the rear defrost switch was glowing on:

Rear Defrost Switch2.jpg

Turning off this switch blows the "IGN/LPS" fuse. I've done it twice to be sure. Has anyone dealt with this before?

Tim

[sirrus]

There is a timer relay in the tailgate for defroster, other than that it’s just wires, switch and the grid. I bet that relay didn’t survive reversed polarity, you can take off tailgate access cover and relay would be on the left.

[TimGee]

There is a timer relay in the tailgate for defroster, other than that it’s just wires, switch and the grid. I bet that relay didn’t survive reversed polarity, you can take off tailgate access cover and relay would be on the left.

Great. I'll check it out tomorrow. Thanks Sirrus.

Tim

[TimGee]

Thanks. Found a post from 2016 from you and candyman.

[TimGee]

There is a timer relay in the tailgate for defroster, other than that it’s just wires, switch and the grid. I bet that relay didn’t survive reversed polarity, you can take off tailgate access cover and relay would be on the left.

Found it.

Defogger relay installed.jpg

Defogger relay.jpg

Can you advise on how to test? Also, any line one where to purchase them? I've searched online. Nothing on eBay or in a google search. Any alternatives from other vehicles?

Thank you.

[sirrus]

I haven’t found that exact one available anywhere, but any timer relay should work if it’s amp rating is enough. You might have to get creative with how to mount a new one though.

How to test it - there should be few wires going to and from relay: power supply (probably always hot, but maybe ACC), signal from dash switch (12 volt when ignition on and switch is on) and output (should be two wires coming off same pin, one goes to defroster grid, other goes to little light in the switch). First check that you have power to relay, then verify that switch works - both can be done with relay unplugged. You can test relay on the bench, supply 12v to power pin, check output pin - should be 0. Then put 12v on switch input (simulating pushing dash switch), output should get 12v. It also should turn off after few minutes on its own, so leave 12v on switch pin and check output after 5 or 10 minutes - should be off

[TimGee]

Thanks Sirrus.

I ended up buying this relay off eBay:

https://www.ebay.com/itm/284249137455?s ... 2749.l2649

It's defined as working with GWs up to 1986 so we'll see. It lacks the pin out for what I think is the ground but I thought it was cheap enough to try out.

I also found a diagram of the relay in an earlier post on ifsja.org:

http://www.ifsja.org/forums/vb/showthread.php?t=164021

http://i307.photobucket.com/albums/nn2 ... 0432e.jpg

So I'll work on that.

I've noticed that when I start up the vehicle the defrost switch light is on and at around 7 minutes (timer) it shuts off and then I hear a buzzing somewhere back at the tailgate. The light turns back on after a couple of minutes and then the buzzing stops.

I called Team Grand Wagoneer and asked if they could find a relay for me and they gave me a number to call. His name is George and he runs a shop called Montana Overland (406) 741-5337. I talked to him and he was really great. He said he had defrost switches and relays on hand but didn't want to sell me one until I checked the wiring going out to the tailgate under the carpeting of the cargo space. He said that the insulation on these wires can get brittle and commonly shorts to the bed of the truck where it channels at the hinge point from the bed to the tailgate. I'm going to check that today and see if there are are any visible shorts.

Tim