Some sort of electrical connector, I have no clue where it goes! See the attached photo.

It wasn't connected when I bought the truck, and I never figured out what it does. My 'water in fuel' light works, so I don't know where it goes.

Some of the early filter housing had a sensor to detect a plugged filter, (it didn't work very well) so I wouldn't worry about it.

My truck has a late model (square) filter. Also, my 'water in fuel' light was on a while back. I drained the water and it stayed on, so I changed the filter and it went away. So I think the sensor is working.

I was looking at it again a little while ago, and there appears to be another disconnected connector hanging down underneath this one. Not sure where that goes, but it looks like the wires go down somewhere by the firewall.

I'm not really worried about it (the truck runs just fine) but I would like to know what it is.

Possibly for an underhood light?

Does it look like the wire that is going down the firewall terminates at the starter solenoid? If so, then something is not getting power with it disconnected...but if everything is working fine....

Possibly for an underhood light?

That could be. The only thing that makes me wonder is that the wires come out of the fuel filter block.

Does it look like the wire that is going down the firewall terminates at the starter solenoid? If so, then something is not getting power with it disconnected...but if everything is working fine....

It is possible that the wires go to the starter solenoid, I don't know for sure. I'll have to check. I wouldn't say that everything is working fine... Lots of little stuff wrong with the truck (rh power window, rh power lock switch, dome light, etc. etc. etc...) I've fixed all the mechanical stuff, so all the engine lights and glow plugs and stuff work though.

It is possible that it did go to an underhood light. I just don't think that it would have come out of the fuel filter block. Who knows though? I'll have to look at it again later today.

I have an actual Chevrolet Workshop Manual for my truck, and that stupid thing does not have an actual wiring diagram?! Amazing.

I also have a Chiltons, which does have a wiring diagram, but since I dont see the fuel filter wiring on it, I question how good it is as well. I also could not find a hood light. Do you know if the 85 had a hood light option?

The chiltons shows a exploded view of the filter. You have a restriction switch, which has two wires. The fuel heater, which also has two wires. And the water sensor, which has 3 wires. If all of these are accounted for, hmmmm...but my guess is that it is one of the above that got broken away from their respective plugs.

Fuel heater... Hmmm. I forgot about that.

It looks like the fuel filter heater connector to me. The filter base has two connectors, i.e., one for the water detector and one for the heater. A single wire goes to the starter solenoid and it usually goes down to the starter along the right front side of the engine to keep it away from the exhaust manifold.