QuestionI have a 1950 Nash 3 speed with overdrive,the overdrive will not engage,there are two wires on the tail end of the transmission a red wire and a black wire the red wire is broken off,I found a unit on the firewall with 4 wires that I believe is for the overdrive and 1 wire is broken off,could this be the wire that should be connected to the transmission,any help on what to do or check to get the overdrive to work would be greatly appreciated,Thanks
AnswerThe two wires from the back of the transmission, if they are way back near where the speedometer cable goes in, are the governor wires. One of those wires should go to the overdrive relay, which is probably the unit you are looking at on the firewall. The other wire from the governor goes to ground, and is most likely the black wire.
The governor provides a switch contact between those two wires when the car is moving above the overdrive cut-in speed - which is somewhere around 25 MPH. What this means is that above that speed, the red wire becomes grounded.
To check out things, with the key on, try shorting the terminal which has the broken wire to ground - see if that makes a loud "click" in the relay and under the car. If it does, that broken wire is probably the only thing wrong with your overdrive; replace it and you're done. If it doesn't make any noise, check the fuse that is on the clips of the overdrive relay and replace it if there is any doubt.
If that doesn't fix it, you will have to get much more involved in the overdrive, including getting the wiring diagram from the shop manual for the car. If you don't have one, get one - it will pay for itself hundreds of times over. Any of the the automobile literature dealers can sell you one. I use Ed Faxon at faxonautolit.com, but there are many others, including eBay.
Once you have the wiring diagram, you can investigate each of the control switches with a multi-meter or even a test light. I can help you with that, but we have to have the diagram to work with.
Dick
