The Borg Warner Overdrive Transmission was offered as an option by eleven different car companies. And as you might expect, each of those car companies developed their own wiring diagram for the Borg Warner Overdrive. They added extra relays, switches etc, nothing that improved or affected how the overdrive itself worked. The simplest and easiest wiring diagram to use by far... is the one developed by Borg Warner.
The picture above shows the Borg Warner overdrive wiring diagram. As you can see it is pretty simple and basic. This diagram can be used for most any Borg Warner Overdrive application.
A Few Notes -
Reverse lockout switches were discontinued by the factory somewhere around the early 1950's. They are not needed and your overdrive will work fine without one. Most original ones no longer work so just bypass the switch. You can either connect both ends of the governor wires going to the reverse lockout switch to the same terminal (which will bypass the switch) or better yet run a new wire down from the governor. Then you will never have to worry about a loose or corroded connection.
There was a recall in the early 1950's... the diameter of the wire that made up the overdrive wiring harnesses was to small in diameter causing, high resistance resulting in an excessive voltage drop and low voltage being delivered to the solenoid and relay, which in turn caused the overdrive to not work, or only work part time. The fix of course was to use larger diameter wire, resulting in less resistance and full current being delivered to the solenoid and relay. The replacement wiring harnesses were made using larger wire which fixed the problem.
So if you are building your own wiring harness I would suggest using 14 gauge wire. The cost difference is minimal and you will not have any issues with low voltage being delivered to the solenoid and relay due to resistance in the overdrive wiring harness.
Generator charging systems, (which most vehicles had that were built before 1965) have little or no output at idle and low engine rpms. So the battery current to run the overdrive at idle and low rpms (such as in town driving) will have to come from the current stored in the physical battery, which is often less that the required 6.5 volts needed to make the overdrive work properly.
You can fudge a little but if the voltage drop is too great between the battery and the solenoid (which can be caused by (electrical friction) resistance from too small of wiring) your overdrive may not engage and work properly, Or may work only at highway speeds, but will not shift in and out in city driving. Anything below 6.0 volts at the number (4) terminal on the solenoid is a sign of trouble.
Also check the voltage on the incoming side of the relay and the output side of the relay going down to the solenoid. There should be little or no voltage drop between those two terminals. A half a volt is the max, and that is if the output voltage going to the solenoid is above 6.0 volts.
You can buy a reproduction overdrive wiring harness but most are made using the smaller diameter wire. Now that you know better, making your own is easy and you know it will be done right. It will be time well spent!
