I done gone f'ed up (fuse box power leads)

[BigD]

Hey guys,

Before I dig into it, I was hoping someone could give me a head start on what I will find and what to do.

So I've begun my 24v swap and I am using someone's garage to remove/install the engine. I took too long pulling the M20 and the owner had to leave, so I cut the engine harness without thinking. So now it turns out I also chopped the two power lines that go to the fuse box from the battery junction.

I'm thinking of getting the lead off a scrap E30 but I first need to know how to remove/connect it. Are there some kind of connectors on the ends of the power leads inside the fuse box, that I can just unplug/plug in? Or are they soldered into the fuse box (or worse yet, the power lead splits and solders in different places)?

Any pics would be extremely appreciated!

Thanks in advance!

[DJB]

The red +12V supply terminates in a ring terminal, with a stud and nut holding it to the fuse box circuit board. You'll be able to unscrew it by removing the screws holding the middle layer of the fuse box to the base, and lifting the middle off a few inches.

That part is trivial. It may be difficult to feed the wire through the rubber boot.

Good luck

[Van Westervelt]

I would just get a heavy duty splice, and heat shrink tube the hell out of it.

[LINUS]

Hey D -

Any reason you aren't inclined to repair it with a soldering iron and some heatshrink tube? Unless there's an easy unhooking on the fuseblock side I'd sooner do that than end up going to all the work of basically R & R your whole box.

If you take your time with the soldering iron you could do a pretty good job, and it seems like a lot less work.

My $.02

[BigD]

I've contemplated reconnecting the wires but my fear is getting enough heat to the bastard for solder (one of them is a real big bitch). I guess I can get a huge crimp, and make sure it flattens the wire out a lot so I don't increase impedance by only contacting the surface...

Disconnecting the wire sounds easy... is the fuse box that hard to take apart? (or do I need to disassemble it even, to remove the ring terminal, DJB?)

Thanks a lot guys!

[StereoInstaller1]

The lowest resistance connection is crimping.

In fact, I recommend against soldering ANYTHING in a car.

Find a set of Hex style crimpers (about 3 feet long) if it is 4GA or bigger, but I don't think anything that big is in the fusebox.

Luke

[Van Westervelt]

The lowest resistance connection is crimping.

In fact, I recommend against soldering ANYTHING in a car.

Luke

Care to expound? :)

[BigD]

Care to expound? :)

^^ x3

I've heard of this before too. When I was making an O2 sensor from a Mustang one, I was gonig to just solder the wires but the instructions I had recommended crimping for a better connection and longevity. I didn't really care since I had a kit handy but I don't really understand why.

Doesn't solder, when it permeates thoroughly, provide a more complete connection? I mean with a crimp, you are limited to only touching the surface area, then unless you can manage to jam the wire butts together, the crimp itself will serve as the conductor and it will have a much smaller cross-sectional area (ie ^^^ resistance).

[StereoInstaller1]

Curt, as I am sure you have noticed, all car manufacturers no longer solder in cars. Crimps have shown themselves to be more reliable, lower resistance, and do not corrode as quickly as solder.

Actual numbers I do not have available, but empirical evidence is overwhelming.

Cut apart the wire around any 10 year old solder joint, you will see.

Luke

[StereoInstaller1]

Sorry D, I was typing as you posted.

Electron theory has it that electron travel is limited to the surface of any wire, but if they become crushed, the electrons will basically jump to any available conductor, so the goal is to make the path easiest.

Solder, while solid, is not terribly conductive...plus the inevitable corrosion of whatever was used as flux "wicking" up the wire making a mess further up the wire.

At least that is my understanding.

Luke

[BigD]

Sorry D, I was typing as you posted.

Electron theory has it that electron travel is limited to the surface of any wire, but if they become crushed, the electrons will basically jump to any available conductor, so the goal is to make the path easiest.

Solder, while solid, is not terribly conductive...plus the inevitable corrosion of whatever was used as flux "wicking" up the wire making a mess further up the wire.

At least that is my understanding.

Luke

Hmm, I know that the resistance of a conductor is proportional to it's thickness and length. If it was just the surface area, I don't understand why the physics books say cross sectional area, not surface area. I mean if it was just the surface, you could then roll a wire flat to get much lower resistance...

[StereoInstaller1]

Read up on Goertz wire. It is flat, and for audio applications, absolutely amazing.


Not that that has anything to do with your issue, but good stuff nonetheless.

[LINUS]

Luke -

I'm not trying to start crap, but that's a pretty "out there" idea that soldering is a worse connection than a butt splice, at least in my head.

I planned to solder all the connections for the wiring harness for my motor swap, but now hearing your POV, it's really odd hearing a wiring guy such as yourself making claims to the benefits of a butt splice.

One of my many jobs in the refinery was to run heat tracing under the insulation on pipes after installing. The instrumentation & electric guys did the final tie in to hot source, but we did the rest.

Point being, there was no butt splicing allowed. Period. And the principle of heat trace is that one line is hot, the other ground - and the material separating them was high resistance coating - generating the heat. This stuff is so sensitive we had to limit runs to 500' , and any connections were soldered, as per the manufacturer's instructions.

They were so specific in every possible situation you might get in with their product that they came out and gave a 1/2 day clinic on their product, because as much as it might seem like simple wire, there was a right & wrong way to install their line for any given situation - elbows, tees, valve bodies, LEDs to show if it was hot, etc.

And the only way they wanted their product connected was solder.


I'm going to go out to the garage and make a test of this this week- if my Fluke is sensitive enough to measure the difference I'll report back my findings.

[BigD]

Hokai, so I got a fusebox/wiring for free, and I took it apart which was trivial as DJB said, but the one I got is from an 88 car, and it has 2 wires where I have my 1. The big one bolts under the fuse box circuit board and a smaller one which goes into the main chassis harness under the fuse box. I cut the small one and pulled out the big one. I thought I was just missing something on my car but I went to look and there are several differences. There are 2 more E30s getting work done where my car is, one is an 89+, and one is an 86. Both have the two power wires going to the battery junction. And the 86 even has the boot in the opposite place - mine has it in the center with the C101 coming out of the one on the side, this one is the other way around. I checked several times and there is only the one big wire going into my fuse box...

So hopefully I'm going to get away with just replacing the big wire and forget about this screwup...