What are these 2 firewall things

[70GMCer]

Still trying to figure out, (among other things), the wiring on my 83.

Can someone tell me what was on the firewall in the outlined circles?

The one is some kind of harness that has been cut out...the blank area looks like maybe some type of relay was there.

[JWall]

The bottom one appears to be the hole for the heat & air conditioning wiring.

[85Misac10]

I believe the top is a vacuum regulator and the bottom one is part of the engine harness

[85Misac10]

It goes to the ecm under the dash.

[70GMCer]

My AC harness looks to be complete. That's the harness in the picture between the 2 outlined circles.

I didn't think an 83 had a ECU. If it's there, it's behind the inside heater box and can't be seen & the truck runs normal.

Might it be the wiring for the cruise control system?

[95 S_Trucker]

The 83 had ESC (electronic spark control)from the factory. Most of them were trashed and a regular HEI distributor was installed.

If your trck had a 700R4, there was a TCC lock up solenoid mounted to the firewall.

[70GMCer]

Originally Posted by 95 S_Trucker

The 83 had ESC (electronic spark control)from the factory. Most of them were trashed and a regular HEI distributor was installed.

If your trck had a 700R4, there was a TCC lock up solenoid mounted to the firewall.

Thanks......That does make since as the SPID says electronic spark control & it does have a HEI dist now.

Not sure about the 700 trans though as it has a 400 turbo in it.

[gezn2]

Yup, that grommet is for the ESC harness and the bare spot above it is the vacuum sensor for it.
A 700R4 would use an identical-looking vacuum sensor on the drivers side firewall.

[RyanNewberry]

I know this isn’t my thread so I apologize but what’s it take to remove the esc harness? Just remove it and install a hei distributor or is there something I’m missing?