Transmission will not shift into 4th after adjusting the brake light switch

[danols15]

Hello

My 1990 XJ will not shift into 4th Gear. The only thing that I have done on it is I was trying to adjust the brake light switch. Now my Tranny will not shift past 3rd??

Please Help,

danols

[longfellow]

This can be a guessing game.
I would reverse my setting on the brake lite back to where it was. Then see if you get 4th gear back. If you don,t than something else has happened.

If you do get 4th gear back then adj. brake lite so it just works.or a hair past that. Then see if you still have 4th gear.

[AlohaBra]

How were you adjusting the brake light switch?

Three questions:
Does it feel like it is kicked down?
What is the engine rpm at 60 mph?
How about at 75 mph?

[danols15]

Thank you for the replys.

Aloha Bra:

60 MPH was about 3000 RPM (had always been about 2000)
Never got her up to 75

My Brake Lights just stopped working and my cruise would not shut off when the brakes were depressed, and I was just trying to slightly move it to see if it would work if it were positioned differnently.

anyway,

I just replaced the switch for the brake lights and now the Tranny is shifting just as I remember it always shifting!

I am happy that this is fixed, however, I really am kind of puzzled as to why this happened.

If anyone knows why the brake light switch would have anything to do with the shifting, I would be very interested to know.

Happy Trails,

Danols15

[AlohaBra]

The brake lamp switch is actually three parts:

1. It goes to the brake lights.
2. It controls the power supply for the cruise control servo.
3. It grounds the brake application sense wiring that tells the cruise when to shut off the cruise system. This ciruitry is located in the Power Train control module, which also controls the transmission.

My guess is that since it got fixed when you changed the switch, the cruise control circuitry was getting signaled wrong. Since the ciruitry is located in the Power Train control module, which also controls the transmission, the transmission was not shifting up, or was in fail safe mode. (Just a guess at this point, without testing the switch to see where it failed.)

Here is a diagram (from the 01 MY) for you to ponder on:

http://www.larrynova.com/Jeep/00/00_...rakeWiring.pdf