Transmission Swap killed my cruise control

[LanceBrad]

Hello all,
I have a '79 Grand Prix LJ (with factory cruise control) that was all original until I took it in to get the transmission repaired/rebuilt. Instead of a rebuild of the original (TH350?), they swapped it out for a TH200-4R. Which, I found out later, was for all intents and purposes, a "good thing".
Prior to the swap, my cruise control worked fine. After the swap, not at all. When I took it in this morning for their "600 mile checkup" I mentioned exactly that, and they said "not sure what's wrong, but we'll take a look and let you know what it'll cost". Of course, I informed them that it was working previously, and he said "it wasn't anything we did, we don't monkey around with that at all".
My suspicion is that they just didn't hook up something that they needed to, but if that's not it, are there any other ideas what might have caused it, or what they might have done (or not done) to cause it?
I'd really like to have it working again since it is original equipment and it worked just fine when I bought it last year.
Much appreciated!!

 

[Ribbedroof]

Your 79 would not have had a lock up converter. So when they swapped to the 2004R they would have had to do some wiring to make the lock up converter work. Potentially that would involve working with the stop lamp switch. Your 79 cruise control would have worked off of the speedometer cable and an optical sensor on the back of the speedometer head. It is possible that if they had to change the brake lamp switch to make theLock up work for the updated transmission that the signal is being canceled by the brake lamp switch.

 

[LanceBrad]

Your 79 would not have had a lock up converter. So when they swapped to the 2004R they would have had to do some wiring to make the lock up converter work. Potentially that would involve working with the stop lamp switch. Your 79 cruise control would have worked off of the speedometer cable and an optical sensor on the back of the speedometer head. It is possible that if they had to change the brake lamp switch to make theLock up work for the updated transmission that the signal is being canceled by the brake lamp switch.

Thanks for the reply.
Any idea what kind of effort (cost) might be involved in making it work again?

 

[Ribbedroof]

Thanks for the reply.
Any idea what kind of effort (cost) might be involved in making it work again?

I would begin with examining the stop lamp switch at the brake pedal. An OE shop manual would be a valuable tool

Does the lockup function?