So after driving the truck uncomfortably now for 6 months I come to find that aamco transmission is full of retards, and my truck does NOT have an a727, it has an a518, the truck has been touched as far as the switch to engage and disengage overdrive, the plug is there but no switch so I can't hook it up to see. I am 100% sure it is a a518 I know what they look like and know what the a727's look like so any ideas on how I can figure out why it's not engaging into overdrive would be appreciated. Thanks.

 

An A518 would have to have been a transplant, 89 through early 91 had 727s stock. That being said, on the drivers side of the transmission you will see a 3 pin connector. That is for park/neutral safety and reverse. Above that, you will find a 2 pin connector, That is the OD connector. Add 12 volts to 1 pin and ground the other through a switch. If it doesn't work with that, then you have an internal problem.