I am installing a a518 behind my 340. I have good, and read a lot of post from all over but still do not understand it fully. If someone has a simple diagram on how to wire it that would be really appreciated I do not plan to install the pressure switch and just want to use a toggle switch for now.

Thanks.

do you have the 3 wire.or 2 wire plug?

3wire.

Looked for a wiring diagram, but the best explanation I've seen so far is HERE

Might be helpful.

I have the vacuum switch and the wiring with both plugs. If you're interested send me a PM. I'll include wiring diagram.

I used toggle switches in my CrewCab
Flipped them at 40 & 50 mph
Took a 155K transmission & shifted it like that for another 50+K before it finally quit

You can hunt all the stuff at the JY to build their lockup kit it involves pulling the pans on a GM 350 lockup & a 700R4 for the pressure switches & the vacuum switches can come from a GM with a lockup tranny

Most trans supply stores will sell the pressure switches for about $10 each. The are for a chevy 350 trans. You will need a 45lb for OD and a 50lb for converter lockup.

The wireing is simple but how you want to control the solenoids can be more complicated. On the three wire plug the center plug is 12 volts and it feeds both the overdrive and lock-up solenoids and the two outer wires are the ground circuits for the overdrive and lock-up solenoids. Basically you just put key on 12 volts to the center wire and then decide how you want to control the two solenoids by grounding the two outer wires which are the Overdrive solenoid and the Lock-up solenoid. When the outer wires are grounding it actuates overdrive or lock-up depending on which one is grounded. I forgot which outer wire is which solenoid. You just have to decide how you want to control the ground on the outer wires to get overdrive gear and the torque converter lock-up. Ron

attached a diagram for what I did with mine.