My overdrive and reverse lights harness perished just through the tranny tunnel where it connects to the transmissin harness and shorted out the fuse. I rebuilt the harness, inspected the transission harness and replaced the fuse, but the overdrive will still not engage. The relay will not click and the dash light will not come on. I inspected and resoldered the relay to no avail. If I removed the yellow wire from the connector that goes to the overdrive solenoid where it goes through the tunnel and apply 12V the solenoid clicks and if I apply 12V will I am driving down the road in any forward gear the overdrive engages as normal. It appears there is a sensor on the top of the tranny, is this a 4th gear lockout switch, and does it appear to be defective. Shouldn't this sensor prevent the overdrive from engaging in anything other then 4th gear. Interestingly while troubleshooting I inadvertently reversed the yellow and black/blue wires at the connector and found that the relay would engage turning on the dash overdrive lamp but not the overdrive solenoid.

If someone has a wiring diagram and knowledge of the principles of operation of this circuit could they please reply. Please e-mail me a wiring diagram with wiring colour codes if possible.

Any replies greatly appreciated

Will Page