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Discussion Starter · #1 ·
I found it amazing that all of the lock up kits range from 20.00 to 180.00 Yet you look in the kit and you get a single terminal 4th gear pressure switch. Some wire, and a few terminal ends. What I have done with my own lock up was fairly easy I already had a 1 wire 4th gear switch and a 2 wire solenoid. So all i had to do was figure out what the hell was going on with the wiring. This is my personal 700r4 lock up Theory. My 700r4 came with a manual body in it.

There are 3 modes of operation for the 700r4 lock up.

( 1 ) Off ( I don't care I consider "Off" a function)
( 2 ) Lock up in 4th gear only
( 3 ) Lock up in 2nd, 3rd, and 4th gears. (A little more involved)

It is easier to understand the wiring if you think of it in two separate steps.

1 Internal wiring
2 External wiring

1 Internal wiring

The internal wirings SOLE purpose is to turn "ON" the lock up solenoid. it's as simple as that.
I would like to refer to the wiring in terms of terminal points instead of colors. There are too many color combinations to deal with.

Starting at the 4 pin plug that is on the drivers side of the transmission

Terminal "A" This runs to one of the two terminals on the temperature switch and then continues to the positive side of the solenoid. End of story there.
Terminal "D" This runs to the second terminal on the temp switch and then continues to the terminal on the fourth gear pressure switch. (switch should only have 1 wire)
Terminal "B" Is the wire coming back out of the transmission which becomes a (negative when 4th gear is engaged or temp switch gets hot (275 deg).
Terminal "C" Is not used. never was.

The wiring inside the transmission is the same no matter which of the following wiring modes is chosen.

External wiring for : Modes 1 & 2

Wiring it up this way will give you the option of modes (1) Off or (2) lock up in 4th gear only.

1 Run a keyed/fused 12v through a toggle switch to the plug marked terminal "A"
2 Connect the wire coming from terminal "B" to the wire going into terminal "D". That's it!

NOTE: Brake switches and vacuum switches are used to turn the lock up "Off"

I put a vacuum switch between the "B" wire and the "D" wire. This drops the lock up "out" on acceleration.
Some people tell you to put a brake switch in to turn "Off" the lock up when braking.
I don't see any advantage to this with a 4th gear only lock up. When slowing down the trans will shift out of 4th and drop out the lock up. Usually before you feel any drag

However if you use the 2nd, 3rd, 4th gear lock up mode I would recommend installing a brake switch.
Down-shifting into 2nd with a locked up converter is pretty harsh on everything involved.

Additional external wiring for : mode 3

Now if you wish to have the lock up work in 2nd, 3rd, and 4th gears. You need to do the following addition to the wiring that you already have done.
You need to connect a ground wire to a second toggle switch and wire it to terminals "B" and "D".
When the switch is "on" the trans will lock up in 2nd, 3rd, and 4th, when the switch is "off" the lock up will only work in 4th gear.

Now.... to add a little spice into the mix I used a Red/Green illuminated ON/OFF/ON switch to do all 3 functions. $7.00
When the switch is up (red light) the trans will lock up in 4th only
When the switch is centered the lock up is "Off"
When the switch is down the (Green light) the switch powers a 12v relay sending a ground to the "B"/"D" terminals giving me the 2nd, 3rd, and 4th lock up.
Simple Eh? If you do this Remember to run the "B" wire to a brake switch then back down to the "D" wire. It's easier on the dental work...

10,121 Posts
I always find it interesting on how many folks are confused by this lock up solenoid system of the 700r4 - 4L60 trans.

it is a very simple 12 volt setup. 12 volts to the solenoid and a ground needed for completion of the circuit if a 2 wire solenoid is used.

I often suggest an internal pressure switch "normally open" type with single pole - self grounding to thread into the valve body.

The problem with an external pressure switch is some 700r4 cases do not have a pressure port near the 2-4 servo on late 1989 cases and newer.

Some of the confusion comes from on "how to route " the 12 volts to the trans case.. these brake light switches with dual circuits in them were usually used for a vehicle with cruise control cancel circuit in them. 4 connectors on them for 2 separate circuit..

1 circuit was Normally Open ( brake lites) , the other Normally Closed (cruise control)

5,030 Posts
Thanks for that run-down, jrs22166- I've made a note of it, so I will pass it on w/credit to you as it's requested, if you don't do it first.

This will save somebody a nice bit 'o cash!
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