View Full Version : Electrical: Overdrive relay Operation

03-03-2013, 02:01 PM
I have been trying to figure out why the overdrive on Dads 50 Champ is not working. The car has been converted to 12V Neg ground. As part of the conversion I purchased a reproduction 12V relay and solenoid from Fifth Avenue Garage.

I think I have traced the problem to the overdrive relay, so I pulled the relay out to bench test it. It is not working the way I expect it to but I can't find a schematic that shows how the relay coil and contacts are connected internally.

My understanding of this relay is that one side of the relay coil gets its ground from the governor. The other side of the coil gets power when the ignition switch is on. The normally open contact gets power through the 10 wag wires coming directly from the battery post on the starter solenoid. The other side of the contact connects to the OD solenoid.

So on the bench I connected the post that normally connects to the governor, to negative 12V. I then connected the post that would normally connect to the ignition switch, to positive 12V. I expected to hear a click and feel the thud of the relay picking up. I got nothing.

Am I correctly understanding the operation of this relay?

03-03-2013, 04:47 PM
There is a very nice picture of how the OD works in the shop manual. The wiring is the same with the conversion to 12 volts.

It sounds like you have the theory of operation correct. The relay coil is not sensitive to polarity. If you connect the coil to 12 volts and ground and it does not click, then the relay is at fault. You might get another one, or check the coil resistance with an ohmmeter. I do not know the resistance you should read, but it should be less than 1000 ohms.

It's possible that a wire is broken inside the case, and you can look inside.

The governor wire also goes through the lockout switch, through the kick down switch to the "bottom" of the relay coil when the system is installed.

03-03-2013, 06:24 PM
Thanks Roy,
I was afraid of that. I guess I will contact Fifth Ave and see what they will do. Sucks to buy a new electrical part and it turn out to be bad. The vendor always claims that you damaged it by hooking it up wrong and you have no way to prove otherwise.