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Discussion Starter · #1 · (Edited)
So Heres a puzzle for you to figure out.

A nice lady brings in an older Expedition.

She says the tranny is shifting really weird.

So a full service is done on the tranny and still no luck.

While this is done a few other minor things are noticed, the third brake light is out, the motor oil is a little low and there are some big scratches in the Side of it.

Whats the Problem?? Why Wont the tranny Shift??

I know the answer as it is fixed and running fine now.

Ill reveal the answer tomorrow. I bet you'll never guess what the problem is.

Just a little brain tinker for fun, it also makes me feel better and better about driving GM.
 

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flopped on its side maybe?
 

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Burned out 3rd brake lite bulb. I seem to remember hearing of a similar scenario a few years ago. I didn't get the answer then and I still don't know why it causes trans problems.
 

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I hate waiting...
 

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I'll second that one.
Hmmmmm. Seems funny to use the 3rd brake light for current supply to the tranny.
Kind of sounds like a torque convertor or the lockup control is acting up.
Again, it seems funny to use that circuit for power though...
Just my $.02 worth
 

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Discussion Starter · #7 ·
Yep. The third brake light is tied into a relay with the tranny.

Ford didnt figure that anybody would drive around with all three of the bulbs burnt out.

Its dumb, but doesnt surprise me.
 

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No kidding?

This gives me an idea...
 

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A friend of mine had a 96 full size BRONCO and had the windshield replaced. Afterwards his tranny wouldn't shift, he had no speedo, no transfer case or dash lights. Turns out they popped the fuse for the auto darkening rearview mirror. This same circuit supplied the feed current for almost half of the body systems modules. I used to think CHRYSLER had some Fed up designs, but after seeing that I changed my mind.
 

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It is wired that way to prevent an accident due to the 3rd light not working, GM did used to kill the cruise on camaros, firebirds, impalas, and caprices if the 3rd light didn't work.
 

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What year/model Fords have this 3rd brake light/trany running on same relay?

Sounds like a Good prank!!!! :D
 
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