73-87 Chevy _ GMC Trucks > Electrical

TH350C orange test connector use?

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Scaryfastatx:
Hi all

I'm trying to get my lockup working on my TH350C to squeeze every bit of mpg out of the old Scottsdale

I want to know what kind of behavior I should be seeing on the orange connector:

- 12v when the clutch should be engaging?
- 12v only when the clutch is engaged?

Thanks?

bd:
For what year model truck are you seeking an answer?

For a 1983 C10 with MV4 (350C) transmission, the orange test connector is used to monitor and verify when 12-volt accessory power is supplied to the transmission TCC circuit through the service brake switch and the low engine vacuum (i.e., high engine load) switch.  There is also a minimum road speed limit switch inside the transmission.  All of the described switches are connected in series with the TCC solenoid, but only the brake switch and low engine vacuum switch are monitored by the orange test connector.  See diagram.

Edited for clarity.

Scaryfastatx:

--- Quote from: bd on March 02, 2026, 01:40:25 pm ---For what year model truck are you seeking an answer?

For a 1983 C10 with MV4 (350C) transmission, the orange test connector is used to monitor and verify when 12-volt accessory power is supplied to the transmission TCC circuit through the service brake [applied] switch and low engine vacuum (i.e., high engine load) switch.  There is also a minimum road speed limit switch inside the transmission.  All of the described switches are connected in series with the TCC solenoid.  See diagram.

--- End quote ---
Thanks for the reply, it's an 81, I think I have everything hooked up correctly according to your diagram

Only difference I see is my 12v supply to the brake switch is pink

My truck had cruise control originally, if that changes anything

I didn't check the brake switch for continuity, will check that next

But was wanting to put a light on the test port to see when I should be engaging the lockup

Sent from my Nokia 8.3 5G using Tapatalk

bd:
Are you attempting to control TCC engagement manually or just monitor the OEM engagement protocol?

Scaryfastatx:
Just monitor the OEM engagement

I'm hoping that I can get it working for the TH350 so when I go to a 700R4 it's working nicely

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