Building a wiring harness - Am I choosing the right ... - PistonHeads

For the pragmatist, there’s not really a reason anymore to wrap a bundle of wires with tape.  Just go to your local hardware store and buy some of that split, corrugated plastic sheathing.  The ‘woven plastic’ sleeve is another contemporary alternative to tape.  Re-taping a wiring harness with tape is for purists only.  Decide which camp you belong to and proceed accordingly.

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Adhesive-backed electrical tape doesn't really belong in the engine compartment of a car.  Sure, it'll look good after you've finished.  And it will probably continue to look good for a few months afterwards.  Over time, though, it's said that the temps under the hood will cause the adhesive to begin to weep out of the seams, after which the harness becomes a grime magnet and a gooey mess (won't be easy to clean either, I expect).  In hotter climates, this may even be a problem for the under-dash wiring harness. 

I recommend that you look into using 'loom tape'.

‘Loom tape’ is just wider-than-normal pvc electrical tape that uses no adhesive.  Back ‘in the day’, this is what vehicle manufacturers (including Nissan) used.  Loom tape is more expensive than high-end electrical tape, but it’s still relatively inexpensive in the grand scheme of ‘things automotive’.  I bought mine from a muscle car restoration parts supplier located north of Toronto.  You should have no difficulty finding a comparable supplier in your own area.  A 100’ roll sells for about US$13.00.  Find vendors by searching on, ‘automotive loom tape’.

Loom tape is typically wrapped with a 50% overlap.  To create this, the tape needs to be wrapped at about 30 degrees off perpendicular.  Or, at least, that’s a good guide for getting started.  After that, you can just adjust on the fly so that you get and maintain the 50% overlap.

Wrapping with loom tape is a two-handed affair. You cannot wrap the tape around the harness using just one hand! You have to pass the tape roll from one hand to the other on every single wrap, while also maintaining a bit of tension during the transfer (warning:  over-tensioning the tape serves no useful purpose and may, in fact, cause problems). No amount of words can explain the actual wrapping process, but it’s not rocket science either and you’ll quickly figure out your own routine. Probably impossible to do with the harness still in the car, though.

Tape all of the branches of the harness first.  Start about 3" from the 'device end' of the branch, wrapping towards the end.  When you get there, turn around and wrap back towards the harness trunk.  When you get to the trunk, do a couple of figure 8's, then wrap down the trunk for about 3".  Cut off the tape, and use a bit of regular electrical tape to hold down the loose end (you'll be wrapping over top of this when you're doing the main trunk).  Do all the branches first.  Then finish up by wrapping the main trunk.  I recommend starting at the firewall end and working towards the front of the car.  Once again, use figure 8's at each of the branch junctions.  When you get to the skinny part of trunk that goes across the front of the car, switch over to the 5/8" wide tape.

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There's a very elegant technique for finishing a wrap.  It involves pulling the loose end of the tape back under the end of the wrap.  Too complicated to explain here (although I found it easy to perform after a couple of practice attempts).  Most people, I think, just tie off the loose end.  If you do all of this properly, you should only have one end where you need to tie things off.  I think you'll be pleased with the results.  Bonus of using loom tape:  If you make a mistake, just unwrap the tape and try it again.

I bought a couple rolls of the no adhesive loom tape for when I redid my engine bay harness. I used Elliott Tape EE 201. It worked really well, but there were a couple things I did notice.

First, I tried to purchase something that had the same gloss (or lack of gloss) as the original stock wrap. But even though I tried to duplicate the original finish, the stuff I ended up with is glossier than the original wrapping tape. And it's more than just "new and clean"... It's glossier. Not a huge amount, but if I was judging the car for originality, it would catch my attention and I would ding it for that.

Second, I've come to the conclusion that the original wrap DID have some kind of adhesive on it. Not the thick rubbery smeary adhesive on the ubiquitous 3M 33+ electrical tape, but I really think there was something there. That said, the non-adhesive loom tape that I used seems to stick to itself quite well and isn't going anywhere despite the fact that there's no adhesive.

I have only had it on there for one year (or was it two?) so I can't provide any longevity info.

If someone turns up a source for the "real" stuff, I'd be interested in a roll or two.

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