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Brake Light Feed Question


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Well here is the quick rundown of whats going on. The truck started out as a 89 4cyl 5spd 2wd and now is sitting in the garage with a 91 4.0 AW4 in the place of the old stuff. I used the 91's engine and dash harness but from the front of the doors to the back of the truck is the stock harness. The truck had 1 harness running down the drivers side that hooks to the dash harness. On that cab harness there are 2 connectors (Black oval 6 pin, Grey square 10 pin). I spliced in the black oval plug into the 91 harness to get the following items to work, Fuel pump, fuel gauge, reverse lamps, left turn, right turn and park lamps. On the grey plug is mostly interior garnish stuff, rear speakers, console lights, switched ground ect. My problem is I can't seem to get the brake lights to work. There is no brake feed wire running in the stock harness. I have a wire left (white/tan) on the 91 harness which is the brake light feed. It's in same plug that the other lights got pulled out of to hook to the MJ harness. So where does it go to power the stop lamps?

 

Thanks,

Chris

 

Everything thing else works, new sockets, bulbs.

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I couldn't find the thread i used to get me started when i did this. Short version, i ran a wire from the #2 pin on the stop lamp switch on the brake pedal to the the P pin on the turn signal connector on the steering column (the long, flat one with 11 connectors, see page 104 in the '91 electrical FSM). IIRC pin P is empty on the XJ connector, so you may want to scavenge a pin from an old harness to use.

 

I was going from a 91/92 dash harness to a 91/92 cab harness, not sure how your mix and match wiring would change things.

 

I've since swapped out that harness for a '96, so the '92 harness is in a box and easily photographed it that would help.

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Are your talking about pin P on the 12 pin connector on the steering column. On the MJ it was a LtBlue/black wire that ran from the 12 pin to the brake switch. On the 91 harness it is empty. I did remove it from the old harness but wasn't sure if I should put it into the 91 column harness and if I did where should it terminate...at the brake switch? The brake switch has 5 or 6 wires in it unlike the stock MJ one with only 2 wire. The doner XJ had all the options like Anti-lock and cruise which would explain the extra wires in the brake switch (to cancel the cruise when the brake is depressed). All the Anti-lock crap was not used when I swapped it over.

On the 91 XJ (page 34, L50 white/tan) wire is the brake feed. I do get power on L50 when I press the brake, so if I have to run a new wire to the rear lamps, well thats what I'll do.

 

-Chris

 

Is pin P feeding brake signal through the steering column to the turn signal wires out back?

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Are your talking about pin P on the 12 pin connector on the steering column.

It's 11 pins on the '91/92 column, is it different on your steering column? The chart below the diagram on p.104 of the '91 FSM lists pin P twice (one for MJ, ones for XJ), so it has 12 rows, but really only 11 pins.

 

On the MJ it was a LtBlue/black wire that ran from the 12 pin to the brake switch

Don't have an older manual, but that wire sounds like the difference between the MJ and XJ dash harness and what you need to get the stop lights working.

 

so if I have to run a new wire to the rear lamps, well thats what I'll do.

On the '91/92 XJ dash harness, the L50 wire continues out of the brake switch and into the rear cab harness. You shouldn't have to do anything else.

 

The brake switch has 5 or 6 wires in it unlike the stock MJ one with only 2 wire.

You're right, most of those wires coming out go to add ons like cruise

1 V32 YL/RD to Ignition of ECU and speed control switch

2 L50 WT/TN to rear lighting via cab harness

3 K29 WT/PK TCU

4 V30 DB/RD speed control servo

5 L9 PK/BK Hazard Flasher in fuse box

6 Z1 BK Chime Module pin A2

 

Is pin P feeding brake signal through the steering column to the turn signal wires out back?

Seems that way. Not sure why they decided to wire it one way in the XJ and differently in the MJ.

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Sorry doing it all from memory from a late night. Your right on the 11 pin. Well thanks for the lead and when I get home tonight I'll hit it again. Hopefully I'll get it banged out tonight, seems like the stupid little things are dragging it out. :roll: But i guess that's what makes it fun.

 

-Chris

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Well thats what it was.

I had to install a wire into pin "P" on the 11 pin connector. The steering column already has a wire in that spot (also from a 91 XJ) but the dash harness it hooks to does not. I hooked the new wire from pin "P" into the black 16 pin XJ connector to the two L50 white/tan stop feed wires...... and now the brake lights work.

 

Thanks again for the help Boilermaker :cheers:

 

-Chris

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yup...clock wiring should be same as any other clock from '84-'86. Here's a copy of the wiring diagram i have for the full system:

http://www.knwd.net/images/MJ/sentry.pdf

 

Hooked up some of the system temporarily before i tore down my truck. Instead of cutting into the dash harness or clock harness, made a little adapter from some junkyard pigtails. Never could figure out what to do with the "Engine Off In" pin that goes to the Choke Heater Relay. I think that's why i had some lights on the monitor go on when i turned the ignition off.

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