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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 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.
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

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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
Title: Re: TH350C orange test connector use?
Post by: Scaryfastatx on June 22, 2026, 12:42:29 pm
So I hooked up a light to the orange plug and routed it to my cluster to see when it comes on

looks like sometimes it comes on off idle at low acceleration, probably at like 10mph, I was under the impression that it wont come on until at least 40mph if I remember right?

I am trying to track down that everything is working on the electrical side so whenever I do a 700R4 swap I can take advantage of the TCC

Thanks!
Title: Re: TH350C orange test connector use?
Post by: VileZambonie on June 23, 2026, 04:48:01 pm
You're reading it wrong. Key on 12v to the solenoid. The brake switch or low vacuum switch can interrupt the circuit open. The pressure switch in the valve body grounds the solenoid when the appropriate pressure is met and applies the torque converter clutch. If you have a test light bulb installed on the test connector you can hit the go pedal and see it go out, let off see it come on, hit the brakes, see it go out, let off the brakes, on and so forth. 
Title: Re: TH350C orange test connector use?
Post by: Scaryfastatx on June 25, 2026, 11:18:01 am
Quote from: VileZambonie on June 23, 2026, 04:48:01 pm
You're reading it wrong. Key on 12v to the solenoid. The brake switch or low vacuum switch can interrupt the circuit open. The pressure switch in the valve body grounds the solenoid when the appropriate pressure is met and applies the torque converter clutch. If you have a test light bulb installed on the test connector you can hit the go pedal and see it go out, let off see it come on, hit the brakes, see it go out, let off the brakes, on and so forth. 

AH ok perfect

I thought the circuits inside the transmission would also play into the test light turning on or off, but its solely checking the: