mystery box & wiring in engine bay - Ford Bronco Forum
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post #1 of 33 (permalink) Old 03-14-2017, 05:46 PM Thread Starter
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mystery box & wiring in engine bay

Let's see if I can figure out the image attachment system...

I've got this mystery box in the engine bay, tucked in behind the air box; set on top for the photos. There's no markings on it. The white cat5 cable runs from one end into the cab (via the junction block on the driver's fender), and from the other end down under the truck in a very sloppy aluminum foil wrap. I haven't yet tried following where either end goes, but I did see the foil wrapped end goes back somewhere when I was under the truck replacing the starter this weekend.

The mystery box's junction block has a red wire connecting to the starter solenoid on the passenger fender.

Any guesses what it is? I've got the 7-pin trailer package and just now figured out that the heavily faded box dangling by a bungee under the dash is a Tekonsha Voyager trailer brake controller, so it's possible it's an add-on for that.







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post #2 of 33 (permalink) Old 03-15-2017, 03:29 AM
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Definitely not cat5. And the box looks like a project box you could have picked up at radio shack years ago. Could be a million things. Let us know where those wires terminate :)


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post #3 of 33 (permalink) Old 03-15-2017, 03:33 AM
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The flat wire coiled up on the firewall looks like POTS or standard telephone wire. Very strange. I see a distribution point mounted to the driver fender. And the wire to your starter solenoid is obviously a power feed for whatever is in the box.

With that being said.... what's in the box??? Is it Jimmy Hoffa??


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post #4 of 33 (permalink) Old 03-15-2017, 03:40 AM Thread Starter
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Cat3? Cat4? I went with the "generic" Cat5 because I figured "cat" would be confusing in car speak. But you may be right that it's not cat cable at all.

My first thought when looking at it, actually, was an alarm system. I've seen no other indication of one, however. That junction block on the fender definitely isn't stock, right?

Admittedly, it was a long shot, but I was hoping it is some common mod that would be familiar to people with more experience than myself. I have a habit of ripping unnecessary stuff out, while cleaning up PO's messes, before ensuring that it truly is unnecessary...

I guess I can start by opening the box and seeing if it contains any hints. There shouldn't be any power to it with key off, but I can double check that or just remove the lead to the starter relay. It's been raining buckets while I've been trying to work on this stuff, making for less than ideal conditions for all but inside work. I'll see if I can follow the big bundle under the dash tomorrow.
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post #5 of 33 (permalink) Old 03-15-2017, 03:42 AM
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CAT 3,4,5 generally has 24 gauge twisted pairs inside. Looks more like security wire as it's a larger gauge.


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post #6 of 33 (permalink) Old 03-15-2017, 03:56 AM Thread Starter
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^ Gotcha.

Here's another thought: If you couldn't guess by the engine bay, it was originally a forest service vehicle. I think they mounted an antenna in place of the tailgate lock, judging from the big circular mark around what would have been the keyhole.

I bet if I follow the aluminum clad white wire bundle, it would head back that direction. However, I haven't yet devised a theory as to why an antenna would be hooked up to the starter relay, or why they wired it under the truck.

Maybe it's just something stupid like a bypass of a faulty fuel pump relay.
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post #7 of 33 (permalink) Old 03-15-2017, 08:55 AM
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An aftermarket radio harness I had once had a box about like that, but it was shoved in behind the radio.

The antenna idea seems logical, other than the wires not being antenna wire.

Where do the other wires go that come off of that non-factory Junction block?
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post #8 of 33 (permalink) Old 03-15-2017, 12:23 PM Thread Starter
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Drum roll please...

The mystery box goes to nothing! I was able to follow it up through the dash, which required dropping the steering column to pull the gauge cluster forward, before finally meeting back up with the cable by a velcro patch at the center of the windshield base.



Maybe it was a hardwired radar detector or something? Not much could have fit in that snug space, unless that was just an anchor because they couldn't get screws back there. There are holes drilled elsewhere in the area.

Here's what the box looks like opened up; doesn't really shed light on its purpose:



Quote:
Originally Posted by BigBlue 94 View Post
An aftermarket radio harness I had once had a box about like that, but it was shoved in behind the radio.
The radio was removed. The stock speakers are still in back but home speaker wire is dangling disconnected. I'm guessing the PO had a couple subs back there. Who knows what else they had hooked up, but it doesn't appear to have been anything high end.

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The antenna idea seems logical, other than the wires not being antenna wire.
Uh, well, er... :) I was thinking in terms of jtetterton's comment that it looked like phone wire, e.g. communications, which turned out to be a good call.
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post #9 of 33 (permalink) Old 03-15-2017, 12:47 PM
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Originally Posted by fodder View Post

Maybe it was a hardwired radar detector or something?

.
My radar detector uses the exact same rj-45 style connector. That would be a good call. looks like it my have piggy-backed into the ignition system so that it only turned on with key-on.

edit*
You said it was a former forestry vehicle? could it possibly have been an early auto GPS setup?

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post #10 of 33 (permalink) Old 03-15-2017, 01:09 PM Thread Starter
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Originally Posted by Teal94 View Post
My radar detector uses the exact same rj-45 style connector. That would be a good call. looks like it my have piggy-backed into the ignition system so that it only turned on with key-on.
I've got the Escort SmartCord system in my other cars, which is why I thought of that. However, while pulling the cord through the firewall and disconnecting the wire to the starter relay, I couldn't help but think back to it having something to do with the trailer setup. I'm wondering if my 7-pin hookup isn't stock, and this somehow filled in the extra wires for trailer braking.

That doesn't entirely make sense either, though, as it doesn't hook up to anything braking related in the engine bay or cabin. Plus, I've got the Tekonsha Voyager trailer brake controller hooked up. It could be the mystery box was the original trailer braking system, and a subsequent owner replaced it with the Tekonsha, leaving the junk in the engine bay.

Tomorrow is supposed to bring a brief break in the rain, so I'll get under the truck and see if I can follow where that wire bundle goes.

Quote:
edit*
You said it was a former forestry vehicle? could it possibly have been an early auto GPS setup?
Could be. That would fit with the apparent antenna mount on the tailgate. I imagine GPS receivers had to be pretty big 25 years ago, especially for remote locations out in the woods.
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post #11 of 33 (permalink) Old 03-15-2017, 02:14 PM
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My guess is a radar signal jammer?
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post #12 of 33 (permalink) Old 03-15-2017, 02:57 PM Thread Starter
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My guess is a radar signal jammer?
I almost mentioned a hidden radar system, then decided that didn't make sense if it was wired to the dash, making it visible. A jammer of some sort sounds plausible and would explain wiring to the rear. It seems like there'd have to be something else up front, though, unless whatever was on the dash did the forward jamming?

I've got a huge list of things I want to be working on on the truck...this rain is really cramping my style! I need to do all the engine bay tune-up stuff, and I'd rather not get everything soaked while it's exposed. I've done about all the interior work I can until getting new parts.
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post #13 of 33 (permalink) Old 03-15-2017, 03:04 PM
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Mine has receptacles for that style cable. Judging by the microphone clipped to the visor, it appeared to be an early mobile phone setup.

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post #14 of 33 (permalink) Old 03-15-2017, 03:15 PM Thread Starter
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Originally Posted by forbye View Post
Mine has receptacles for that style cable. Judging by the microphone clipped to the visor, it appeared to be an early mobile phone setup.
That would be along the same lines as the early GPS guess, and would also explain a big antenna in back. If that was the case on mine, they probably mounted it to the dash instead of the visor.
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post #15 of 33 (permalink) Old 03-15-2017, 04:17 PM
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Quote:
Originally Posted by forbye View Post
Mine has receptacles for that style cable. Judging by the microphone clipped to the visor, it appeared to be an early mobile phone setup.
That makes a lot of sense. The 90's were full of bag phones and hardwired car phones. Used one to call my uncle when i was 8, when our 93 f150 flipped over as he was closer than any emergency responders in the area would have been.

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post #16 of 33 (permalink) Old 03-15-2017, 05:09 PM Thread Starter
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Well, we were all way off with our guesses! The rain kinda sorta let up, just enough to get some cardboard under there before it turned to complete mush. I followed the white wire bundle back until it became just one red wire. That in turn follows the frame rail further back and, to my surprise, splices into the rear diff! Speed sensor? Gearing control?

It's a 2-wire loom to the drive shaft, with white and green wires. The mystery box's red wire is spliced to the white wire. It looks like the green wire was also tapped into at some point and taped back up.



Here's where the wire loom connects up to the rear diff:



Also note that the plug seems like it has too much wire pulled through to clip over the metal lip without bending the wires badly.

Here's the routing of the mystery red wire before it splices in, along with a vacant hose (ABS?) up high:

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post #17 of 33 (permalink) Old 03-15-2017, 05:44 PM
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The "vacant hose" is the vent for the differential housing

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post #18 of 33 (permalink) Old 03-15-2017, 05:53 PM Thread Starter
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Originally Posted by Mikey350 View Post
The "vacant hose" is the vent for the differential housing
Good to know, thanks. I couldn't make my way over to the other side to see if it had the same thing, and it looked to be attaching right near the brake line on the side pictured.

I'm new to 4x4's and didn't even know diff housings have vent hoses. :)
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post #19 of 33 (permalink) Old 03-15-2017, 06:09 PM
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Since it was a Gov't vehicle perhaps it is a tattler system

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post #20 of 33 (permalink) Old 03-15-2017, 06:16 PM Thread Starter
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I'm new to 4x4's...
Quote:
Originally Posted by JScatt View Post
Since it was a Gov't vehicle perhaps it is a tattler system
I was about to look up what a "tattler system" is, then realized what you meant... That could be, some sort of monitoring of how the vehicle was driven.

Unless someone comes up with a reason why it should remain, I plan to clip it tomorrow and re-wrap the wires around the splice point.
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