FDR

I am a complete newbie at this, so if I'm asking a stupid question please bear with me. I am helping my 17 year old son rebuild an 86 C10 and we had the dash out to put on a new cover and install a new radio. After I put it back together I can not get the transmission to shift at all. It seems to be stuck in neutral. I did find a 3 wire plug that I can't find a place to plug it into so I don't know if this is related or not. The wires are pink/black, yellow, and black

. During all this work the truck was sitting inside and not moved at all. Sometimes with it running I'll hear what sounds like gears meshing when I move the lever to park, but that is the only time I get any activity when moving the shift lever. This is an automatic. Anyone know what I could be missing?

kevinkpk

Isolate the linkage from the transmission, go from there, is it the linkage, or transmission.

FDR

Nothing changed in the transmission. I drove it into my shop, installed the radio and when I went to move it out it would not shift.

Kazoocruiser

What a strange coincidence. How long has the vehicle been sitting?

Have you checked the level of the fluid in the transmission with the dipstick?

How many miles are on the odometer and especially transmission?

What color is the transmission fluid?

Does it smell burned?

Maybe all the friction material stripped out in a worn-out transmission floated to the bottom of the pan and clogged the filter, so the pump can't develop pressure.