1994 ZJ with serious brake light issues......... - JeepForum.com
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Unread 11-26-2014, 03:38 PM   #1
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Join Date: Nov 2014
Location: santa cruz, ca
Posts: 3
1994 ZJ with serious brake light issues.........

1994 grand cherokee laredo 5.2 with factory tow package

So in the process of replacing a factory tow "7 pin" plug with a new one since the factory/old one was heavily corroded my brake lights have stopped working.

The running lights/headlights, turn signals (front/rear) and backup lamps all work. the brake lights worked fine prior to the tow plug removal/install.

I've already located the 3 relays, circuit breaker and complete tow harness behind the passenger's rear panel and unplugged it all from the main harness. No effect.

I've determined there is 12v going through the brake light fuse on the passengers side dash panel and replaced it just to make sure. no effect

I've also checked for 12v at the brake light switch on the pedal. I have V coming in from a red wire/green tracer with key on/off and a brown wire/ no tracer with key on only. Once "switched" I read V coming out through a white wire/tan tracer. I also grabbed a junkyard switch and swapped it, no effect.

I've pulled both tail light housings and checked all the bulbs as well as the 3rd brake light bulbs and all are the correct model # and functional.

For giggles I also disconnect both posts of the battery and left it overnight to see if there was something to reset. no effect

The car does have an add on alarm done by previous owner. i currently don't use it and it has given me no troubles since i've owned the car. Not familiar with alarm wiring so not sure if anything would tie into the brake light circuit?

I don't have a Haynes manual for this car so I can't look at a full wiring diagram, had no luck finding one online either specially for my specific year. Is there a brake light relay, additional fuse, circuit breaker or fusible link somewhere? Anywhere else I might look for a short or a problem? It didn't look like it but I read while googling that some of these housings have a circuit board inside? There are no contact prongs to "bend out" on my housings where the sockets snap into. I'm usually good with wiring having wired countless carbed cars from scratch but these newer cars make things so complicated I'm honestly lost on where to look next. Any help or tips would be greatly appreciated!

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Unread 11-26-2014, 04:34 PM   #2
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1996 ZJ 
Join Date: May 2014
Location: Green Bay, WI
Posts: 51
I had this problem when I installed my trailer wiring harness. The one I got was the 4 wire harness without brake light connection. It seems you need to have that 5th wire in the circuit to make the vehicles lights work. I replaced the 4 flat with a harness from Curt Mfg and everything works as it should.

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Unread 11-27-2014, 10:35 AM   #3
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Join Date: Nov 2014
Location: santa cruz, ca
Posts: 3
My harness, 7 pin plug and class VI hitch were all factory installed. everything worked fine until i went to change out the corroded male connector to an identical replacement. So I would assume that the problem should be fixable without buying or changing anything as far as the connector. I did forget to disconnect the battery while doing the swap so my thinking is that i might have shorted out something in the circuit by accident. Question is what or where?

I should add that when my camper is hooked up everything works on it (running lights, backup lights, turn signals, power to trailer) with the exception of the brake lights. Camper plugged or unplugged the cherokee's brake lights still don't work.

7 pin connector in question

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