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700R4 TCC wiring help needed

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77crewcab

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I am installing a 700R4 in a Monte Carlo that origionally had a TH400. I have everything installed except the 700R4 wiring. I am using harness pieces from an 82 model C10, but it has been butchered some. I have the plug/pigtail for the trans. (3 wires tan/blk stripe, purple/wht stripe, green), I have the vacuum/electrical thing on the firewall and the plug/pigtail for it. (don't have it infront of me to look at wire colors) What all do I need under the dash?
 
Okay I went and got the rest of the harness I have for the firewall/underdash. I have the vacuum switch on the firewall and the harness from it to the switch on the pedal.

From the vacuum switch I have two green wires (from the same pin on the plug) one has been cut. there is also a blue wire it has been cut. The remaining green wire connects to a plug for the underdash harness. That plug also has a blue wire that has been cut but is the wrong length to match up to the plug on the vacuum switch.

The harness then goes through the firewall. Once through the firewall I have a green wire with a plug on it. It was not plugged into anything on the truck and no apparent mate for it. The blue wire goes to the brake pedal switch, which also has a black/wht stripe that goes to the fuse panel.

Questions:

Do I need to have the cruise vacuum line hooked to the brake pedal switch if the car doesen't have cruise? Does this need to be capped?

The green wire coming through the firewall, what does it need to be connected to?

The small harness from the vacuum switch to the under dash harness. Are the two blue wires supposed to be connected together or is there something supposed to go between them (cruise maybe?) Also what does the extra green wire from the vacuum switch connect to?

Which wires do I need to connect to the plug on the transmission and which wires do I match up?
 
Essentially, the system runs from the fuse block, to the brake switch, from the brake switch to the vacuum switch, and from there to the transmission. Only one wire needs to be hot going into the transmission, it grounds internally. The other wires are un-needed in the installation.

As far as the cruise control bit goes, if there is suction on that hose while the engine is running, it needs to be capped
 
Okay so since the power is coming through the firewall to the vaccuum switch on the blue wire, I assume that I need to connect one of the green wires at the vaccuum switch to the trans plug. Is this correct? and which pin on the trans plug do I connect the power to? This is a 90 model 700 if that makes a difference. Do the other two wires on the trans plug need to be connected to anything?
 
Unfortunately, I can't remember which pin is used on the transmission, been a long time since I've owned a truck with a 700r4. So yes, you need to run power from the fuse block to the brake switch, from the brake switch to the vacuum switch, then from the vacuum switch to the transmission.

You may just need to drop the pan and take a look and see which pin runs to the lockup solenoid
 
Usually there are two circuits going to the trans.
1) Broken only by the brake switch - gives you lockup whenever you are in 4th gear. Inside the trans this one passes through a 4-3 downshift solenoid (unlocks for shifting) and a pressure switch on 4th gear pressure.
2) Broken by the brake switch and the vacuum switch - manages the lockup in 3rd gear. Usually there is a valve that runs from TV pressure and governor pressure to determine when lockup should be allowed. So 2nd/3rd gear lockup depends on both electrical and hydraulic signals.

There is another circuit used sometimes, which is actually an output. It is to let the EGR and/or charcoal canister work while the TCC is locked up for cruise. You probably won't need this.
 
Is that picture your trans or are you sure it's exactly like yours? Is this from a carb or ECM truck? I have a number of wiring diagrams here, but none of them match yours. The best I can see:

Terminal A has a red wire going directly to the solenoid.
Terminal B has a tan wire going to the 4-3 downshift switch (N.C.)
Terminal C is empty
Terminal D has a black wire going directly to the solenoid.

From the 4-3 downshift switch is a brown wire going to the 4th pressure switch.

Is this correct? If so, you run 12V to terminal A and then tie B and D together. This will give you lockup only in 4th gear. If you want lockup in 3rd, then you will need to wire a ground connection through the vacuum switch and brake pedal switch to apply ground to terminal D (still tied to B).

All you HAVE to have is lockup in 4th. Lockup in 3rd gear helps with economy a little. It's especially nice if you travel a lot around 45mph or so and can't quite get into 4th gear. Not having lockup in lower gears is actually a little better for performance.
 
That pic is not mine but is wired exactly the same. Mine is still dripping fluid from dropping the pan and I didn't want to get tranny fluid on my good camera but my phone doesn't take decent pics to post.

Terminal A has a red wire going directly to the solenoid.
Terminal B has a tan wire going to the 4-3 downshift switch (N.C.)
Terminal C is empty
Terminal D has a black wire going directly to the 4-3 switch
Black wire from the 4-3 switch to the solenoid

From the 4-3 downshift switch is a brown wire going to the 4th pressure switch.


I forget which wires share a common pin on the 2 prong 4-3 switch and I didn't get a good pic of it on my phone.

So if I am getting it right to have 4th lockup only I need to only connect the red wire to 12v. That 12v will go through the vaccuum switch, to the brake switch, then to 12v on the fuse panel. There is not a fuse from the factory on this harness and in was plugged into a ign port. Do I need to add a fuse and if so what size?
 
That solenoid only uses a couple milliamps, just plug it into an ignition port and don't worry about it :)
 
Is the black wire tied in with the tan wire on the 4-3 switch? If so, you don't have to connect B&D together on the outside.

You can't wire pin A through the vacuum switch, because it's your only power source for lockup. In 4th gear, the TCC should be locked all the time, regardless of vacuum. The only thing that should be allowed to unlock it (other than the downshift) is the brake switch. (This is usually how people troubleshoot the lockup. You drive in 4th and then push the brake just enough to trigger the switch and if the rpms come up, that is the converter unlocking).

I think your tranny is an ECM model, which is why I was saying above that you would have to make up your own circuit for non/OD lockup.
 
Okay on the 3-4 switch the tan/brown are on one pin and both black wires on the second pin. Do I still need to hook B/D together?
 
I've always hooked mine up to allow the converter to unlock in 4th gear during high load situations (aka, use the vacuum switch). I've never used the 3rd gear lockup option, and I am of the opinion that it can lead to premature failure of the transmission. There is good reason why GM quit locking the transmission up in 3rd gear when TBI came around.

If you are in a rush, just hook up the 4th gear lockup as I described above, and call her good!
 
77crewcab said:
Okay on the 3-4 switch the tan/brown are on one pin and both black wires on the second pin. Do I still need to hook B/D together?
Click to expand...
OK, based on this, you don't need to tie anything together outside. The solenoid grounds through the 4th gear pressure switch. You only need to bring in 1 hot wire to the transmission.

If you wanted to do 3rd gear lockup I could explain it to you, but it would be different from the factory configuration.
 
Russell said:
I've always hooked mine up to allow the converter to unlock in 4th gear during high load situations (aka, use the vacuum switch).
Click to expand...
The 700 does not cool very well in 4th gear. The higher the load, the more heat the converter will make, so it really needs to be locked. If you want more torque, have it downshift. If you want to talk about "there must be a reason why..." look at how all of the factory configurations lock up all the time in 4th.

If it works for you, great. For anybody else coming across this thread I wanted to be sure the other side was presented.
 
Fair enough! I guess for me I always found that my previous gutless 350s could use that extra umph in 4th gear to get up a hill without shifting back to 3rd. I totally agree with you on the point of extra heat being produced whenever they are unlocked in 4th gear
 
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