Under the coolant bottle on my 1990 is this unknown wire sticking out of the harness. See photo. It is a single wire (black w/red tracer) that has some sort of push on connector ( same as the connector
for the temperature gauge in the head only straight). There is nothing near it unconnected. Does anyone have any ideas what it may be for?

 

Under hood light?

 

What about the one laying in the bottom that looks like it has a yellow ESD cap on it?

 

Here is my "under hood light" plug, assuming its correct. You can see the red w/ black tracer. I don't have a light in mine though.

It goes to the large collection of wires on the firewall, just to the inside of the coolant bottle, up top.

 

Looks like yours has 2 red w/ black tracers. mine is just 1, along with another black.

 

It is not the underhood light. I have removed that to fix the retracting mechanism. The wiring for that is shown coiled up with the electrical tape on it and with a yellow cap over the connector. The light has two wires

 

Are you the original owner? Maybe it was a clever way for something else to be spliced in for power....????
I found another plug under the hood not being used while I was taking those pics..... Same wiring harness, different vehicles ..

 

I see what you mean by taped up with yellow cap. Followed the wire, and I can see the red and black ones.....

 

I bought it from the original owner over 25 years ago. He was a good friend, in fact I went with him when he test drove it. I'm pretty sure he did not monkey with it. He always had the dealer service it. I managed to
steal it away from him after his second kid because his wife complained about how hard it was to get them in and out of the small rear doors. As an update - the connector is only live when the ignition is on. The wire and connector
look too factory be be an add on. The wiring harness looks untouched and in good condition ,so I do not want to go chasing it. It has not bothered any thing in the past quarter century, so I will just put a vacuum plug over it. I was just curious
as to what it might be for especially since it has gone unnoticed all these years.