So I picked up this 86 hatchback a couple weeks ago, got it running & have been tinkering with it. Anyways, it has this black box mounted on the passenger side fire wall. I believe the red wire went to the + on the battery. The rest was soldered together, the blue wire from the box to a red wire on a toggle switch & a thick black wire that ended up going to nothing .... Anyone have any clue as to what this could be for ? A relay ? Alarm ? It has no lettering or anything on it so I can't look it up online, I just took it out of my car as its obviously not for anything ....

 

 

Pulled out the black wire to find it not connected to anything

I also have this yellow wire that spliced under neath my carpet in the back, right along the tranny tunnel

 

Car is an ea81 '86 hatch back

They soldered it to shielded coax!? Huh? Well, unless it grounded through the housing, not enough wires for a relay but it still could be. Maybe the had the fuel pump jury-rigged at some point. The other thing that comes to mind is an RF suppressor/filter. Why they would tap a power feed off of it to a switch is a bit perplexing unless they had an older FM modulated CD changer in the car. The switch would have had filtered B+ to turn on the modulator which in turn turns on the changer. The coax would have been the power back to the changer and maybe their thought was using the shielded coax would reduce any RF after the filter. Good idea, but poorly applied as soldering to the shielding in the coax renders it useless. The shielding should have been grounded to the chassis to bleed off the RF. I'm leaning towards this idea as the box looks similar to the older, generic RF filters. For those who are not quite sure what I'm referring to.... Ever install audio equiptment in a car and get that annoying 'audio tachometer' (whine) from the speakers? That is RF (radio frequency) intereference. It bleeds through the power wires to the stereo from either the alt or coil. The RF filter 'cleans' the power signal up so you don't get the whine.

It could be but I have never seen one like that.. I have a  few in the garage.  I responded in his build thread. It kinda looks like a valet box for some type of alarm system.  All I can do is speculate without tracing the wires back to the respective ends.

Generally, they are round with four wires, but I had one that looked like that in a parts box around here somewhere.... lol

Perhaps a power cleanup for a CB setup???

 

With the Yellow wire inside the cab being the 12v?  and the coax being from the antenna preiously then hacked due to ignorance for whatever reason???