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AT Overdrive Switch Inverter
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Using a Relay to Invert the OD switch position
This modification reverses the O/D switch, so it stays off until you press it to go activate O/D.
Posted by Evan A. Beck to the TDR Forum: It's a VERY easy thing to do... I came up with this one night, and was surprised how simple it is. All you need is a regular accessory relay and some wire.
But first, some info on how the OD switch works. TO turn OD on or off, it requires a pulse of ground, which is what the OD switch does. It is a momentary-contact type switch, and when you press it, it gives ground to the PCM telling it to turn OD on or off. ***FYI, the Ford E4OD and 4R100 work the same way, but just use 12V+ to the PCM instead of ground.
So basically, all you need to do is give the PCM a ground pulse when you start the truck. Standard relay terminals are:
When you turn the key to the START position, it will trigger the coil in the relay, and give ground to the OD switch wire going to the PCM, thereby locking out OD, until the button is pushed. Basically, it would be like holding the OD button down while you start the truck. It works. Try it.
For 2001 Rams - Posted to the TDRoundtable by Garrett (Big White Beast)
For the 2001 the starter relay wire is yellow and it runs through the clutch in switch which is just a jumper on the AT's. I hooked the positive of a 24V relay to the wire on the clutch in switch. The negative to ground and then jumpered the ground to common on the relay. Then the orange with white stripe wire coming from the OD switch is tied to N.O. on the relay. At start up the relay activates and gives a ground pulse to the OD switch turning it off. Just pull off the knee plate under the dash and everything is right there. Plenty of room to mount the relay too.