Converter lock-up function, (4L60)

[MagicRat]

1983 GMC Vandura, 3/4 ton (G-20) with a 305/auto.(THM 700R4) 80,000 original miles

I bought this van at about 65,000 miles, and the TC lock-up did not work, but other wise the trans worked well for 10k miles. Then an annulus (ring) gear broke.

I replaced the trans with a recently-rebuilt used 1991 4L60, which had the identical 3-wire wiring harness. The TC lock-up does not work on the new trans, either.

So I am assuming the lock-up controller does not work. This van is Canadian, and uses a coolant temp switch and a vacuum switch wired in series to control the lock up. It looks like the vacuum switch is seized.

So, I would like to temporarily hook up a manual TC lock-up switch.

Can I just apply 12 volts to the appropriate wire going into the transmission to get it to lock up? If so, which wire is it? The green one?

Thank you.

[MT-2500]

Originally Posted by MagicRat

1983 GMC Vandura, 3/4 ton (G-20) with a 305/auto.(THM 700R4) 80,000 original miles

I bought this van at about 65,000 miles, and the TC lock-up did not work, but other wise the trans worked well for 10k miles. Then an annulus (ring) gear broke.

I replaced the trans with a recently-rebuilt used 1991 4L60, which had the identical 3-wire wiring harness. The TC lock-up does not work on the new trans, either.

So I am assuming the lock-up controller does not work. This van is Canadian, and uses a coolant temp switch and a vacuum switch wired in series to control the lock up. It looks like the vacuum switch is seized.

So, I would like to temporarily hook up a manual TC lock-up switch.

Can I just apply 12 volts to the appropriate wire going into the transmission to get it to lock up? If so, which wire is it? The green one?

Thank you.

My wiring diagram shows on pin no.
Wire on pin A from TCC brake switch to transmission plug should feed 12 volts to the wire a circuit with brake switch close.

Inside transmission wire a goes threw the 3-4 pulse switch and on threw lockup solenoid.
From lockup solenoid the ground side is pin wire D that runs back to pcm.
The vacuum switch I would just jump it.
I do not have the wiring circuit on vacuum switch.
Not sure tcc even runs threw it.

If you can find a older transmission hand book it should have the TCC wiring and vacume switch wiring diagram in it.

[Blue Bowtie]

You can replace the vacuum switch with a manual switch, but understand that the vacuum switch is intended to sense engine load and drop the TCC under moderate and heavier loads.