Best way to Reshield wiring?

[rs4pro3]

I'm starting to do a motronic 1.3 conversion to my 1981 633csi from L-jet. Problem is only one year harness will work from an 89 635i and they are super hard to find. So I've desided to lengthen a 1.3 harness from some of the easier to find cars. I have to lengthen the section betweent he firewall grommet and the ECU connector about 1-1.5 feet. There are 4 or 5 groups of shielded wires and I'll have to cut them open lengthen and some how reshield so ECU noise and other electrical noise dosn't interfere. What's the best product to use?

[Ryan Stewart]

Man, that is going to be somewhat difficult. Go find some shieled security wires or fire alarm panel and wires. You need to have a drain wire too and make sure the shielding is prevented from grounding to anything on the body. It has to act as an antenna to to draw the noise away.

[rs4pro3]

Ya I know it's going to be fun :roll:

[EverWiser]

I'm shooting in the dark so forgive me if what I recommend doesn't make much sense...

If you are lengthening an existing harness that has shielded cables/wires, it would be advantageous to change out the entire length of shielded wire with an equivalent type. An electrical supply store could get you what you need; probably a "Belden" brand cable that you can specify the gauge and number of conductors that you want. Belden makes a lot of different styles but one with a foil wrap AND shield wire will be the best for noise rejection.

Now, if you are just going to lengthen a harness by splicing wire in between one end and the other, there's a few things you will need to do. HOPEFULLY, there is a shield wire on both ends that you can tie into. The same electrical supply store that you could have gotten the Belden cable from should carry grounding braid which is basically a flattened tube of tinned/weaved wire. You can open it up and run your splices through it and then stretch it along the wires and it will act like "Chinese handcuffs" and tighten up around the bundle. You should make sure that you use a section of braid long enough to overlap the existing harness and then solder the shields from the existing harness to the section of braid you just added.

Whichever you do, make sure the shield wires are only grounded on one end. Preferably all of the shields should be grounded/terminated to or near the same grounding point. If you ground them on both ends you get what is called a "ground loop" which can allow current to flow through the shield and thus negate any benefit of having the wires shielded.

If you follow this advice, there is NO WAY you will have any problems with electrical noise. I hope this helps...

[rs4pro3]

Replacing the whole wire would be to hard. What I'm planning on doing is splicing in a section of shielded wire in each of the 4 spots where there is shielded wire. I've got a few junk engine harness that I've cut 3 2 foot sections of shielded wire out of and I'll just splice it in. Then wrap the spliced areas with foil and shrink wrap it and each individual splice. It will remain grounded at the factory splice by the ECU plug. I'll probally start digging in tommorow, by laying the harness in the engine bay and figuring exactly how much longer it needs to be, then go buy the appropiate guage and ruff color of wire(not red soldered to black wires :roll: ) Should be fun. But worth it in the end to have the 6 running on a much more modern fuel injection versus the Old L-jetronic.

[Ryan Stewart]

if you could replace the wire it would be best but if you can keep a drain running along the shield and overlap the shield while protecting it from everythign else would be key.

its gonna be bulky though.

[EverWiser]

Replacing the whole wire would be to hard. What I'm planning on doing is splicing in a section of shielded wire in each of the 4 spots where there is shielded wire. I've got a few junk engine harness that I've cut 3 2 foot sections of shielded wire out of and I'll just splice it in. Then wrap the spliced areas with foil and shrink wrap it and each individual splice. It will remain grounded at the factory splice by the ECU plug. I'll probally start digging in tommorow, by laying the harness in the engine bay and figuring exactly how much longer it needs to be, then go buy the appropiate guage and ruff color of wire(not red soldered to black wires :roll: ) Should be fun. But worth it in the end to have the 6 running on a much more modern fuel injection versus the Old L-jetronic.

Should work fine...Make sure you've got good continuity (resistance reading very, very close to zero ohms) on your completed splices even when flexing them and what not. Some solder on the spliced shields/foil will go a long way in making sure no noise will get onto the signals. Good Luck...

[rs4pro3]

Ya I'm planning on soldering everything. I'm not a fan of crimp connectors.