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73-87 Chevy _ GMC Trucks => Electrical => Topic started by: Scaryfastatx on March 01, 2026, 06:24:03 pm

Title: TH350C orange test connector use?
Post by: Scaryfastatx on March 01, 2026, 06:24:03 pm

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?

Title: Re: TH350C orange test connector use?
Post by: 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.

Title: Re: TH350C orange test connector use?
Post by: Scaryfastatx on March 03, 2026, 12:17:24 pm

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.

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

Title: Re: TH350C orange test connector use?
Post by: bd on March 03, 2026, 01:29:38 pm

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

Title: Re: TH350C orange test connector use?
Post by: Scaryfastatx on March 03, 2026, 01:48:30 pm

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