Splicing into an Engine Wiring Harness

phelan did pass the time by typing:

Nothing wrong, providing it's done correctly. :)

Do not use plugs or crimp splices. They will corrode and in a few years cause all sorts of problems. Another problem is the resistance. Some wires in the harness are very sensitive to resistance/bad connections.

Re-insulations works but over that long a reach with burned out wires I wouldn't.

When you splice in wires do it one at a time, use a heat shrink insulation and the proper solder teqnique on clean shiny copper. Stagger the splices so you don't wind up with one whopping cluster.

A fairly good howto with pics

Soldering works great. I rebuilt my CJ7 harness and soldered in a whole bunch of replacement plugs and sockets and pigtails. This was 5 or 6 years ago with no failures.

They now make an automotive double walled 'weatherproof' heat shrink that works really well. It is full of a heat activated epoxy. This also acts as stress relief. When I did mine, I used dielectric grease on the connections with heat shrink over them.

Like someone else mentioned, I always stagger the connections so the area doesn't bulge and still fits inside the loom.

There is only one connection that must be crimped together. That would be the small brown wire from the alternator where it joins a soft fat red wire to a regular 10 ga red wire right around the brake reservoir inside the loom that crosses the firewall. The soft wire is a resistor wire to the coil power and needs to be crimped.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail >

In the engine compartment, you want to be certain that the splices have mechanical strength as well as a sound soldered electrical connection. Google for "Western Union Splice".

When I was in grade school, we had vocational classes where we used fifty year old manuals that were very big on Western Union Splices, and that's the way we learned. They're designed for solid wire, but I use them for braided too.

I'll add my emphatic vote against crimped connectors of any kind here. That's what a dealership would do.

Hth, Fred Klingener

05 Jeep CK 73 Porsche 911T 38 Rolls Royce 25/30

I was thinking the same thing. For Jeeps from a decade earlier all he'd have to do would be to trot down to the local boneyard, pull one bolt from the center of the firewall connector and yoink out the engine harness half, complete with connector block, leaving the lighting harness behind. Way quicker and easier than leaning over a fender all day, splicing wires. Did electrical systems change much by `88 to prevent this?

L.W.(ßill) Hughes III wrote:

Ah. It might be regional/business differences. In my neck of the woods most (but not all) the cars I see in boneyards still have their engines in place, and that's where they stay when they go to the chipper. Tires and gas tanks come off, everything else metallic ends up on a boat to China.

L.W.(ßill) Hughes III wrote:

Stuff like this can be easily, quickly, and permanently fixed with crimps. They make a type that has an heat-shrink insulator, so squeeze some dielectric grease in, crimp the wires, heat shrink the insulator, and you are done. The dielectric will prevent any moisture from getting in and corroding. Tie the whole mess away from the exhaust with some Adel clamps to prevent having to do it again. It's only a car, why waste time overdoing it?

Been an electronics technician for 20 years.... Don't use crimp connectors or reinsulate with electrical tape. Both are bad practices. Do it right, and solder in new wires. I'd recommend you go to the boneyard as someone else said and find that part of the wire loom, cut out the part you need keeping everything intact from the bad area to the terminus of each wire as practically as possible and replace the whole shooting match. Stagger the solder connections, use rosin core not acid core solder, and be sure to use flux on the wires. First and foremost if you don't have experience at soldering, PRACTICE on some other wires to get the technique down before going in. Soldering is very easy with a bit of practice and guidance. Lastly use heatshrink on each connection and make sure it forms a tight seal.

Howard,

As an auto-electrician by trade, I'd be inclined to cut out the burnt section, and replace it. For an application within the engine bay, a solder/heatshrink combination would probably provide you with the longest service life. Sure, it'll take a little longer, but should result in many years of hassle-free operation :)

Aside from that - ensure the replacement wire is the same gauge as the burnt stuff, (if not a little larger), and you're good to go.

Jas.

Stupendous Man proclaimed:

Some even come with the grease pre-installed. If you have the correct crimp tool and connector, there is no need to heat shrink, as you crimp the connector onto the conductor, then onto the insulator or both at once with the more expensive die based tools.

Being an electronics design engineer with special background in manufacturing and service engineering, I'd have to strongly disagree with you. For a big consulting fee, I could even prove it with statistics. Or ask why there are no solder joints in a modern car.

The typical untrained person attempting to solder is going to do more damage than good. In my experience troubleshooting complex military and mainframes after some doofus decided to solder, there aren't that many NASA grade trained solder technicians that can do it right every time compared to using a good foolproof latching die based crimp tool. Worse are the techs who thought it was a good idea to solder the crimped connector "just for safety".

A good gas tight crimp is actually superior to solder anyway. That is why no modern computer has used solder connections in the wiring looms for decades. Before crimp, wire wrap was more reliable once the issues of making sure it is gas tight and teflon wire cold flow were identified.

A modern protective gel filled crimp connector properly applied and crimped beats any solder joint for mechanical and electrical integrity.

Rich proclaimed:

Lon, There is validity to what you say, but our original poster is repairing wiring on an old Wrangler not an F-117. The crimp-on connectors he's probably going to be buying are going to come from somewhere like Car-Quest or Pep-Boys. Cheap junk on a good day. While I by no means profess to be an engineer I do have real world experience with electronics in all types of environments including salt water. I still assert that he'd do better soldering and properly heat shrinking. If he were fixing a B2 Bomber or a SPY-1 Radar I'd say you might be right. Put it in perspective.

I spent my first few years as a mechanic working on VWs., so i got to fix a lot of fire-damaged harnesses, and later vOLVO CAME OUT WITH SOME THAT (oops) just fell apart. Customers can't always afford an $800 engine harness on a $1000 car, so I have fixed quite a few of those, too. I use crimpers like this,

but mine are made by Kline. I wouldn't use the cheap stamped type except as a temporary emergency fix. When you pack the joint full of compound and crimp, it squished the stuff up the wire a ways and prevents corrosion. Not as nice or quite as resistance free as a soldered joint, but you can't make a living doing Rolls Royce quality repairs on Hyundais. It works, and I have some joints on my Jeepster that I did this way 15 years ago and they are still clean..

You may be right... I get spoiled by having Frys as the *low* end of readily available decent electronics parts. Plus I should mention that there is no good, cheap, crimp tool. The good ones all have separate dies for every wire and/or insulation size combination--plus they use a ratcheting action such that the jaws won't open until the tool has been closed to provide a proper crimp.

As for automobile versus aerospace, we disagree. What works for one works quite nicely for the other with appropriate consideration for the environment. e.g. what is good for a bomber is rarely good enough for an automobile, particularly one known to have a taste for mud and water.

That's why I recommended sticking purely to the pre-gelled crimp fittings. So far, I haven't run across any of those of crappy quality like some of the stuff sold in blister paks at cheap parts stores. The gel is nice, particularly for jeepers in keeping crud out of the crimp.

As for cutting out the old wiring, I would hope that is obvious. I'd recommend cutting several inches past any insulation that is at all discolored, misshapen, etc. The next part is that you need to clean the old wiring before crimping. I use a mild metal pickle, then rinse carefully and a fine glass abrasive brush to make sure totally clean and unoxidized metal is exposed to the crimp.

Of course if it were my vehicle, I'd consider a replacement harness that I could pick apart and put in as necessary, ideally with mimimal use of the old stuff.

Rich proclaimed: