I still refer to your oiling mods regularly, Good job/good tech & much appreciated!

Might need two switched plumbed in a T, one for lower pressure, one for the higher pressure. Then a relay controlled by the switches. Use the ground from the high pressure switch to the relay coil ground, This will close the relay at the higher pressure setting. Wire the lower pressure ground to a one side of a set of NO contacts on the relay, jumper the other side on that pair of contacts to the relay coil ground, this will let the low pressure switch control the opening of the relay. Remember to wire the relay coil + to a switched 12V source.

On the second set of NO contacts on the relay run a ground to one side then run the other side to activate the circuit.

How this circuit will work is like this. As the pressure rises the low side switch will make, since it is going to a set of NO contacts on the relay the signal stops there as the relay is deenergized. Pressure continues to rise until the high side switch makes, this sends a ground to the coil negative, if you remembered to wire the coil + then the relay closes. With the relay closed you now have both sets of NO contacts closed. Your circuit will energize. The ground from the low side is now applied to the relay coil - as well. At this point both the high pressure and low pressure switches are applying a ground to the relay coil -, not a problem. As pressure drops the high pressure switch will open and remove it's ground from the relay coil -, but the low side ground will still be there thru the now closed contacts. Once pressure drops enough for the low pressure switch to open the ground will be removed from the relay coil - and the relay will open removing the ground from your circuit. At this point pressure will have to rise enough to close the high pressure switch and the cycle starts over.

Short of finding an adj hi/lo switch this is how I would do it.

If you want a single pole I can draw that up for you

....This is why your home air compressor shuts off at 120psi and kicks on again at 90. If it didn't that thing would running darn near all the time. ......

DaytonaTurbo hit it with the air compressor example. If all you want is a deadband, then get a pressure switch with not only an adjustable setpoint but an adjustable deadband. Then you don't need all the space shuttle circuitry.

I put 2 timers in so it doesn't search, Tranny has to be in OD 10 sec or LU won't happen.

The 518 (46RH) is hydraulically controlled and uses 2 servos to enable the OD and LU.
The 3-pin connector on the transmission supplies the control voltages.
The center pin always has 12V power connected. The 2 outer pins are switched grounds. The front pin is the OD ground, the rear pin is the LU ground.

The module works according to the following sequence.
1) The 12V toggle switch supplies voltage to the relays and transmission center pin.
2) When the hydraulic pressure trips (50mph/adjustable) the pressure switch, ground is supplied to the vacuum switch. When speed is below 50mph, hydraulic switch opens, disabling OD.
3) When there is enough vacuum, the vacuum switch closes, providing the OD relay ground. Under heavy acceleration, vacuum drops, opens switch, OD is disabled.
4) When OD relay has ground and 12V, it waits 10sec, then supplies 12V to the LU relay and ground to the transmission OD pin, enabling OD.
5) Now the LU relay has 12V, it's already grounded. It waits the 10 sec programmable delay then provides ground to the transmission LU pin. So lock up doesn't occur until OD has been enabled and on for 10sec.
6) The programmable delays for both relays fix the situation when speed is fluctuating around 50mph. This would normally cause the OD to kick on/off, the 10 sec (programmable) delay stops this from happening.