[OUPony]

This wire comes out of a harness right above the brake reservoir on a 1968 Ford Mustang. It looks pretty useless to me....BUT, what is it?

Is it important???? Please help!!

[Jay H 237]

I see the wiring behind it for the signals in the hood so that's not it. It was the first thing I thought when I read the thread title.

It looks to me to be a mercury switch mounted to the hood, as if it's part of an alarm system, or what's left of one. If the hood was opened with the alarm activated it would set the alarm off. They may have followed the factory harness through the firewall for ease of installation and not having to drill a hole. Does it appear to be part of the harness (actually coming out of it) or does it just follow it or appear to have been added to the harness by wrapping it with tape around the outside. It's possible some previous owner added an alarm and then they or someone else removed most of it except for this.

The only other factory plug I know of that leaves the harness near the master cylinder other than for the turn signals in the hood is the wire for the brake pressure warning light switch that attaches to the brake line junction block. Do you have this wire going to the switch?

I looked on my '68 coupe and there are 2 white with blue stripe wires and 2 green with white stripe wires leaving here for the hood signals. There are also 2 violet wires with white stripes for the brake pressure switch. That's a total of 6 wires leaving the main harness near the master cylinder.

[Cracker289]

Are you sure it's a mercury switch and not a light bulb?

Also consider the possibility that it is a sensor off the engine that someone at some previous time took off, and just found a covenient place to stick it rather than correctly reinstall it.

[OUPony]

After a little research and some testing, I found (and activated) the alarm system for the car. That is in deed a mercury switch for the tazor 4 alarm system. The previous owner installed an alarm system but did not provide me with any information about it.

A google search later, I got the manual and re-activated the system.

Thanks for your responses, I had no idea what it was.