The wires travel through the firewall through a grommet, and one of them ends in an orange plug. The other wire disappears into the inky black darkness behind the steering column.

 

Probably a sensor or switch of some kind, That bracket with the bolt-hole looks like there was once something there, which may have been part of what this device did. Lots of corrosion and rust . so I am guessing this is an old vehicle. What is the year, make,model of this vehicle? Looks to me like someone has been messing with it, or removed something, by what I can see so far.

 

does it look like a vacuum line goes to it...looks like a old chunk of tubing on one end. maybe a vacuum port that is electrically switched? hard to say without knowing the make model year.

 

Looks like a solenoid with the part that is activated missing.

 

Thanks oilcanhenry, the bracket you are referring to with the hole missing is part of the brake booster support. I've already tried to put a bolt in the hole, and it is a blind hole. Nothing will screw into it. I think the booster support is for more than one vehicle.

The truck is a 1981 C10 with a 4.1 / 250 longbed Scottsdale.

I'll probably go out and use my "scope on a rope" testlight on it today to see if any wires carries power to it

 

It is a 3-wire switch. Check your dash to see if you have any kind of "fuel economy" light on the dash. This might be a switch to light up that warning bulb. I had the same thing on an old Ford years ago and it was the sending unit for a fuel economy warning light.

 

Hi, it's me again with a progress update. After spending much time cogitating on this problem, I found wiring diagrams in the ST-330-81 service manual that I was able to find and download. The diagram for the switch was located on page 1113. Turns out it is supposed to actuate the lock-up feature in the torque converter, which currently isn't connected. I don't even think the power tap has been run to the fuse panel. So I have to sort that out, as well as figure out how to run a correct vacuum signal to it, because I think it needs that, too.

 

I just got back from looking under my dash, and sure enough, the blue wire runs to the brake switch, and the red wire that is supposed to go to the fuse panel wasn't connected. Someone had disconnected it and put the wire behind the panel. So now I have power through the brake switch, to the blue wire to the switch I pictured in the original post. For some reason, I can't get pictures to upload.

 

Yeah, tech2 had it down pat with the vacuum hose. I haven't seen anything like that part before. Without the lock-up torque converter operating, it's costing you gasoline. I dont know why the previous owner performed this, but I have seen worse.

 

The switch is still available for those wanting to wire in a converter clutch. Turns out ported vacuum pulls the switch open and breaks the electrical feed when you accelerate.

https://www.classicparts.com/1982-86...ctinfo/53-604/

Whoever pulled a multi-vacuum 3 port switch out of the thermostat housing to install a water temperature gauge allowed a monkey under the hood of the truck.