87' Grand Wagoneer Defrost Relay work around

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TimGee
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Joined: Wed Apr 28, 2021 3:01 pm

87' Grand Wagoneer Defrost Relay work around

Post by TimGee » Tue Jun 15, 2021 10:36 am

I've been having issues with the tail gate glass defrost. Previously when you start the truck the rear defrost switch defaulted to 'On'. When I tried to turn it off it would blow the IGN/LMPS fuse that powers the gauges. Thinking it was a faulty defrost timer relay I ordered one from eBay: 'Grand Wagoneer "Jeep AMC Heated Rear Window 75-86 Relay NOS 5454614"

https://www.ebay.com/itm/284249137455

Here's the original installed:

Defogger relay installed.jpg

But when I installed the 'new' one and it behaved the same - defaulted to on and blew the fuse when I tried to turn it off. Instead of tracking down the issue any further we bypassed the relay and now the switch on the dash is just a constant on/off switch. Problem solved. No more blown fuse.
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1987 Jeep Grand Wagoneer. 360ci V8. Holly Fuel Injection

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Stuka
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Re: 87' Grand Wagoneer Defrost Relay work around

Post by Stuka » Wed Jun 16, 2021 6:27 am

So its clear you have a short some place. I have posted a wiring diagram below (technically for an 85, but I don't think it changed from there on).

With you bypassing the timer switch, does the defroster light no longer come on? If not, the short is most likely in the defroster light. As the fuse that was blowing for you is not directly related to the defroster outside of the light to say that it is on.

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Topic author
TimGee
Posts: 26
Joined: Wed Apr 28, 2021 3:01 pm

Re: 87' Grand Wagoneer Defrost Relay work around

Post by TimGee » Wed Jun 16, 2021 8:43 am

Stuka wrote:
Wed Jun 16, 2021 6:27 am
So its clear you have a short some place. I have posted a wiring diagram below (technically for an 85, but I don't think it changed from there on).

With you bypassing the timer switch, does the defroster light no longer come on?
Hey Stuka,

The switch's light functions as it should with the relay bypassed. I haven't tested to see if the defrost wires are powered or not. It's on the list!

I'm bringing the truck into a mechanic here in SLC so I'll mention the relay issue to them. The truck is having a hard time turning over in the morning and it idles very roughly. My skill set isn't up to diagnosing engine issues or most electrical.

If anyone has a recommendation for a Jeep mechanic in the Salt Lake Valley it would be most appreciated.

Tim
1987 Jeep Grand Wagoneer. 360ci V8. Holly Fuel Injection

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