A loom that was doomed 

The wiring loom was in a dire state, and had been modified by previous owners time and time again. In some cases, the multi-plugs had been cut off, presumably during faultfinding, and the remaining wires twined together and taped up. Wow. I had masses of problems with the wiring, lights flashing on and off, not flashing battery drawing down etc. There was only one way round it, and that was to re-build the loom. Below are the methods I used. Maybe not to everyone's taste and in some cases far too much work involved, but this is how I did it.

First, remove the loom; it's nearly impossible to make a good job of it on the bike. Take loads of digital pictures of the plugs and wire locations on the bike, and/or take notes.

Then buy a second hand loom. It doesnít matter how bad it is as long as itís all there. Ask if all the multi-plugs are present, and if any modifications have been made. For the XS750 there are minor differences between all the years, so try to get the right one, though for our needs it shouldnít make much difference.

The one I got was from a 2D model and cost £6 ($10.50US or Ä8.70) from eBay. The guy threw in the tank mount rubbers, the battery box rubbers and the helmet lock. I think £10 would be a fair price for a half decent loom. I'm fairly certain that I was really really lucky. My bike is the E model.

Remove all the multi-plugs from the donor wiring loom using a crimp removal tool or a fine pair of tweezers if you donít have one. (As I did) Do not cut any wires at this stage. Also make sure that you take careful notes of the wire colours, the plug type, crimp type and position of the originals.

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To remove the crimp look inside the plug and youíll see a small holding tag. Use the tweezers to squeeze this in then pull the wire carefully from the back.

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Take all the crimps out in the same way and put the plug heads in white spirit and clean with an old paintbrush. Youíll now have a complete set of nearly new looking spare plugs.

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Here's a picture of one I'd cleaned compared to one I hadn't touched.

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Before you start taking your good loom apart, I suggest you clean the whole thing with white spirit and a cloth, and then remove all the black tape. The one below has about half the black tape removed. Remove all the black nylon shroud/sleeve as well. Most of it will be burst or kinked anyway. The junctions or joins will be taped up separately, so leave them as they are just now. This will hold the loom together.

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Once the tape is off, clean all the cables with a spirit dampened cloth, and get all the mucky goo off.

You will find that the loom looks like it has been repaired in places, and that it has been soldered together. It may have either blue or yellow insulating tape over these connections. Fear not. Yamaha built the looms this way, and made these joins inside the loom. Take the tape off them, but unless the connection looks crusty or loose, leave well alone. If youíre confident soldering, heat it, clean it with a solder sucker, flux it and re-solder it. I would cover it with a similar colour of insulating tape when youíre finished, not black, otherwise it wont be as obvious next time you repair it (Next time?)

Now, take the crimps out of the plugs on your loom one at a time and transfer them one at a time to the donor plugs (Previously cleaned), cleaning the crimp with an abrasive paper, fine brass brush (Like suede brush) or just wipe it with the spirit cloth. You may need to gently bend the holding tag back out to make sure it catches the inside of the plug. If the conductor material looks like the one below, dull and matted, it is a good idea to solder the connection as an additional measure. Relying on the pressure of the crimp for a good connection will be Ok but not great. When you add 5 or 6 connections similar to this throughout the loom, you start to loose voltage, and the system is only 12 volts. The bike is between 25 and 30 years old.

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To solder the connections, youíll need to make a good job of cleaning the crimp and cable without removing it. I did this by cleaning the surface of the connection joint with the suede brass brush, and then some solder flux. Only then would the solder take and pool into the connection. Take care not to overheat the connection and melt the insulation. At this point you may need your donor loom to repair your own. Remove all the tape and shrouding and clean as before.

If like me you had sections of the wiring loom damaged, then cut these out of the donor loom near the main run as below. Bare back about 5-6 mm of conductor on each wire and cover in flux. Solder together and insulate using heat shrink for the best job, or insulating tape wrapped very tight around each connection individually, then as one around the outside. Don't over wrap it as this will cause a bulge. When grafting sections into the loom, allow a couple of extra inches (50mm) in length to the piece that you put in, as these looms were a tight fit to the frame. As you are using the correct plugs and wires, all the colours will match up, as will the plugs, but be sure to check. I had a couple of minor differences with the colours but the loom you get could be different. The key is to have lots of notes and photos before you start for reference.

You have been warned.

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It's also a good idea to build up a list of what you need before you start.

Consider a good pair of non-insulated crimping pliers which are totally different to normal crimping pliers.

Get at least a 25 watt soldering bolt, some solder, and solder flux, maybe a heat resistant pad.

Buy spare crimps, tape and most importantly buy in some serious massage creams.

Yes massage creams. You heard me!! No matter what height your work area is, you're gonna be sore. Trust me. Here is a list of the different types of parts you'll come across

Crimps 6.3mm Non-insulated female and male crimps. Available from AES online.

These must be the tagged kind shown or they wont stay in the plugs.

Bullet connectors. I was unable to source the correct ones so re-furbished the old ones.

AES had two types, neither of which fit the plugs.

Black PVC sleeve. Available from AES online

Black insulating tape. Available from AES online .

Blade Fuse Boxes. Available from AES online.

They are available in small quantities and are very fairly priced. This is just the place I used; I'm not affiliated to them in any way. Please call them before you buy and use your best judgment, as you normally would when using any supplier for the first time.