I have a '86 IROC with the LG4 and a T-5 tranny. The tranny went out recently and for the sake of saving money I found a rebuilt transmission from an '87 Trans Am. It bolted right in and everything connected beautifully, but, my back up lights do not work at all, and the up shift light comes on even when I am in 5th gear. I am not too worried about the shift light, I can just disconnect it if it continues to bother me, but I really would like to have back up lights. Please help.

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Pimpin' ain't easy.

 

If I remember correctly, the reverse switch is on the body of the transmission itself, you may just need to replace it.

As for the upshift light, the only thing I can guess is that the signal is dependant on the VSS and ECM, since you haven't changed ECM's, the VSS isn't functioning properly.

Enlighten me here, I can't remember when they switch to electronic speedo's in Camaro's and Firebirds, but i belive your problem lies in the VSS somehow.

 

In 86 it is still a cable speedometer.

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Pimpin' ain't easy.

 

If the VSS circuit is working, then the new trans 5th gear ratio may be the problem. The ECM calculates when to turn on the shift light based on the VSS output and the engine RPM. It may be that the 5th gear ratio is different in the new T5. G92 cars got the 0.73:1 ratio 5th gear, which would make the engine RPM higher than it was at a given MPH compared to the non G92 T5 5th geat ratio of 0.63:1. Did you swap the rear end gear ratio, too? If so, that would cause the shift light problem, too. The PROM would have to be changed to compensate for the new trans or rear end ratio to fix the problem.

Tim