Few wiring questions

[Psycho_Bob]

I have an '81 C10 stepside that I am putting together as a tow vehicle.  I have recently swapped from a TH 350 to a TH 350c with a lockup converter.  The new transmission has a 4 prong plug on the side of it for torque converter lock-up.  I also have a wire hanging down from the wire loom that runs behind the distributor that runs down to the transmission area that has this same style of connector but with 2 prongs instead of the 4 on the trans side.  I am going to make the assumption that this connector is for the lockup, but when I look for the vacuum switch that controls the signal to the converter, it is not there.  It is mapped out on the vacuum diagram on the radiator support but there is no tee in that particular circuit for it, and the switch itself is not mounted to the firewall.  Is this just one of those red herring plugs that come with all harnesses regardless of whether the feature is being used?  Also, what would it take to add the feature into mine if it wasn't originally there.  I could just add a toggle switch for highway driving, but that just seems tacky.

Thanks in advance

[Lt.Del]

Call me tacky. 
My Th350c has a two-prong female plug.  I have noticed at wrecking yards that some have 4-prong plugs. I guess it depends on the year of the tranny.

Because my 79 didn't have a lockup feature, I didn't really care to add the brake switch, distr. switch, vacuum line, etc...I just put on a toggle switch near the dash and just keep it on when I am driving--deosent matter if i come to a stop or driving in the city, it wont lock up until I drive over 35 miles an hour.
I just ran a 12 volt wire from the toggle to the interior part of the two-prong plug and taped it really well.

[Psycho_Bob]

I may just forego the switch then and tap the fuel pump wire that runs through there.  Thanks for the advice.

[Lt.Del]

What works for me may not necessarily works for you.  You may not want 12 volts going to it all the time like I do.  There are times, sometimes pulling something, sometimes passing someoned, that I switch off the lock up feature.  There are times when driving near 40 if i give it gas, it will keep switching back and forth between lock up and non lockup--that gets irritating sometimes and I just flip the switch off.

Also there may be some styles of th350c's that may not automatically switch off the lock up when slowing down and accelerating in passing gear, etc....mine will automatically switch out from the lock up feature.  You may want to have a switched 12 v current to it just to see what yours will do  and if all checks out, then put an ignition switched voltage to it. 

Just some things to consider.

[Psycho_Bob]

Will I need to ground the D-terminal on my trans connector?  I put +12 to the A-terminal and it did not appear to drop the RPM's any at 55 mph.

[HAULIN IT]

Bob, What are you going to "tap into the fuel pump wire" for? What switch are you going to forego, the toggle or vacuum? Just want to make sure we're all on the same page. 

[Lt.Del]

On my th350c with the two-wire plug (not sure about your 4-wire plug), one was for the 12 volt, the other was for negative.  I didn't worry about the negative, since, several bolts connect the tranny to the engine. Didn't see the need.

[Psycho_Bob]

My stock trans connector is the two connector plug, but there is only one wire attached to it for the +12 volts.  The other prong was not made to have a wire on it as far as i can tell.  My trans has the four prong plug with A and D terminals actually wired up.  I have read in different places where the solenoid is internally grounded in some but not all models.  The way mine acts, I may have to go ahead and ground that D terminal to get the solenoid to fire.  If it doesn't act properly locked up all the time, I may go ahead and add the vacuum switches to the system.  I am primarily going to use this truck for trailering, BTW.

Bob, What are you going to "tap into the fuel pump wire" for? What switch are you going to forego, the toggle or vacuum? Just want to make sure we're all on the same page. 

I am going to tap the fuel pump wire (ACC) to run the lockup converter on my new lockup transmission, since the stock wiring is not complete for this feature.

[Psycho_Bob]

I was incorrect when I said that the vacuum switch for the lockup circuit was not there.  As it turns out, the hose had just been disconnected and the switch was partially hidden my the brake booster.  I may put the line back in the appropriate place in the vacuum circuit and put a test light on the lockup wire and see if everything works.

[VileZambonie]

If you are just running a toggle switch make sure that #1 it's rated for the amount of current you are running through it and #2 that you don't forget to switch it off (PITA)

I would wire it just like it was factory. I've posted a few diagrams on how you can wire it or how the factory did it if you search.