I want to wire my Torque Converter Clutch in my 1986 K5 Blazer back to stock. I have everything running from the dash and engine compartment to the transmission wiring harness, but can't find a stock wiring diagram for the transmission harness. I have a light blue stock wire coming down from the vacuum switch mounted on the firewall. I also have a light green stock wire coming down from the 4-wheel drive relay under the dash. I assume the third wire in the transmission TCC harness will go to ground. Since I have an aftermarket wiring harness, the wire colors don't match. I installed a 383 crate motor, so I don't have an EGR. The truck came stock with a 305. I have the shop manual but it doesn't have a wiring diagram for this harness.


Looking down from above on the installed TCC wiring harness:
Purple wire is front, drivers side
Blue wire is front, passenger side
Tan wire is rear, drivers side
Rear, passenger side is not wired


Light Blue wire from Vacuum Switch?
Light Green wire from 4-Wheel Drive Relay?


I appreciate any help.

 

Seems I only find answers after I post a question. I found this diagram in the shop manual. I figured I'd post my own answer in case anyone else is looking for the same diagram. I will test drive tomorrow.

 

I took the K5 for a test drive and the truck shifts into 4th very well then I can feel the torque converter lock up. This is all very smooth and the truck runs and drives great. The only problem now is that I can feel the TCC staying locked up when I'm coasting down hill with my foot off the gas. If I tap the brake, it unlocks and rolls smoothly. I have researched this issue using my shop manual, this forum, and some other sites and found the following list of things to check:

1. Change vacuum switch from manifold vacuum to ported vacuum (haven't tried this yet)
2. Inspect the TCC solenoid for external ground short (unlikely since I just wired it, covered all wires, and made sure everything was routed away from the headers)
3. Inspect the converter for internal damage (not sure how to do this unless I remove the converter. If I go that far, I will probably just replace it.)
4. Inspect the oil pump assembly for the converter clutch apply valve sticking. This requires dropping the transmission oil pan. (not clear on where the valve is yet, but I have the shop manual and can follow the diagram)

Does anyone have any advice? I'm hoping someone has already tackled this problem and has a story to tell. The truck drives so smoothly now, I know I'm close. I'm open to suggestions.

 

I'm just going to keep posting my own responses until a transmission expert sees my desperation and gives me some advice. I checked the vacuum switch and found it is already connected to the ported vacuum source on the carb. Since I just wired the TCC and loomed the new wiring, I don't think an external ground is the problem. I double checked and the wiring is clear of the headers and looks good. I'm not sure how to check the torque converter for internal damage without removing it completely. I have not yet dropped the transmission oil pan to change the filter, check the pump, check the TCC valve, or confirm the internal wiring is good.

 

in my 88 hopped up rx7 with a 350 and a 2004r i used a adjustable vacuum switch so i could fine tune the lockups maybe that will work for you also

 

Thanks for the tip. I will test the stock vacuum switch for engine the rpm ranges where the switch kicks in and out to ensure mine is operating as designed. I see switches like yours for about $30. Is that what you'd expect for that type of switch?

 

I built REX and have owned her for about ten years now - I think at that time the vac switch was about 20 to 25 dollars so with inflation that price you found is prob about right
edit
I've been thinking more about your problem - the TC is going to stay locked in until the transmission shifts into third gear from 4th or you manually disengage it by stepping on the brake or the throttle , the vacuum switch is going to disengage the lock up when vacuum drops by stepping on the throttle - Check the adjustment of the TV cable, if it's out of adjustment it might be keeping the pressures too high in the valve body - also maybe the springs on the governor, 200 4r and 700 4rs occasionally throw them - REX has no computers and a edelbrock carb. so I bought a conversion kit from Bowtie Overdrives for the TV cable to fit the carb along with it i bought the lockup kit and it came with the 4th gear psi sensor, brake switch, new lockup solenoid, relay and the wiring harness - I'll keep burning the grey matter and see if I can think of anything else i did

 

I used to have a 4th gear pressure switch that I used in a home-made lockup wiring kit. Everything is now back to stock for the TCC but what if I wire the stock power through the 4th gear switch? Theoretically, when the truck is coasting, there should not be pressure from 4th gear to activate the switch and the converter should unlock.

 

Thanks for devoting some thought to my problem Odat. I tested the vacuum switch today. It is normally open and closes with about 4 in/Hg of vacuum. If I had an adjustable switch, I'd probably kick it up one in/Hg at a time and see how it affected the TCC lockup. Does anyone know if I can find a junkyard donor with a switch that opens/closes at around 7 or 8 in/Hg?

 

Clark - In theory and if I remember right mine is wired this way - if your lock up solenoid and 4TH gear pressure switch are two wire units run fused power to one of the wires on the solenoid. the other wire off the solenoid runs too one terminal on the 4TH gear switch then the other terminal on the switch runs out of the trans up to the vacuum switch from there too the brake switch - the two wire units are easier too hook up but i do know there is a way to do one wire units id have to research that way of hookup