I am sure we have all done it! Pored over the outside of a beautiful restoration and admired the quality of the welding, the glossy, smooth paintwork and the freshly re-chromed metal. Then we open the bonnet and find the wiring to be a disaster. Even within the pages of specialist magazines it seems okay to show an image of an engine bay full of un-taped wires running everywhere, cable tied to accelerator or choke cables or even twisted together and disguised in garish colours of insulating tape. Now maybe it’s because I learned my trade as an auto electrician in the seventies but such disregard for an essential part of any vehicle curls my toes.
For some reason many people (including some of the best mechanics in the land) are scared of vehicle electrics. There is no need for this and hopefully this article will show how relatively easy and straight forward it can be to build a suitable wiring harness for your classic van. With a little thought and planning, anyone can do it and the parts are readily available. This is the rebuild of the wiring harness for the maroon coloured JB van.
So what do we need? Firstly, suitable tools: a decent set of terminal crimpers are essential along with a good knife, cable strippers and a soldering iron and solder. Black harness tape, the type of which will depend on the vehicle you are working on. Cloth tape and cloth harness tape will suit older vehicles whereas PVC harness tape will suit later examples. At one point in my life I did try using coloured insulating tape thinking that it would identify my work. It identified it alright; it looked blooming awful! So now it is black tape and only black tape. For the main harness use the non-sticky harness tape as opposed to run off the mill insulating tape. Adhesive tapes can be used for rough assembling of the harness prior to final taping.
Cable! For this van we considered two types of cable available which are cotton covered and PVC. Although the van would originally have had PVC cable it was felt that cotton covered cable would give a more pleasing finish. PVC cable is easier to work with and easier to strip the ends than with cotton coverings. Cotton cable does require a little more care while working with it.
Now that we had decided which cable type we were using we now needed to remove the old harness and measure it. It was a lot easier removing gauges, lights etc., to gain more access, the space when re-building is much more appreciated . It also allows additional tasks like re-chroming the gauge bezels for instance.
Being methodical is vital! Keep a note of anything you may want to remember and even take photographs as a reminder as to where everything went.
Make a wiring diagram! Actually you will need two diagrams. Once the old harness has been removed, draw a rough wiring diagram. It doesn’t have to be a work of art, just as long as you understand it. If necessary use a knife to carefully remove the old tape and work out where each wire goes, and note the colours. Make a note of the various terminals in case you need to order replacements. Now, measure the various sections of wiring to work out how much you need to order. Don’t worry about adding on an extra metre or so. It’s always best to have too much and cut it back rather than coming up an inch short. This is where you need the second diagram. Lay the harness on the floor and draw a schematic of the various branches of the harness along with their respective lengths. You can Assemble the new harness by lying it over the old one but the chances are the old wiring will be filthy and there is no point in buying nice bright new white cable only for it to become grey before it’s even fitted. Our wiring diagrams were jotted down on the back of an old cardboard box, it doesn’t matter as long as there is some sort of reference.
Building the new harness. Now that your lovely bunch of nice new wires have arrived, it’s time to get down to the business end of things. Most cables will come either on a roll or in small round bunches. This makes building a straight harness quite tricky. The secret is to take the longest few wires. Probably ones which will stretch from the dashboard to the rear of the car will be suitable. Cut them to length. Now tie one end to a solid object like a bench and stretch out and tie the other end to something else like a workmate or a stool or similar. Once you have a straightened wire, the rest will fall into place easily. Start to add in the rest of the cables you need depending on where they are going. For instance add in all the wires going to the right hand front lights, then the left and so on. Using the schematic you made earlier tape the harness where the branches are going to come off. Tape the harness at roughly 30 cm intervals to hold it together. Use normal adhesive insulating tape for this task. Refer to your main wiring diagram to make sure you don’t forget anything. It is much easier to add an extra wire at this stage should it be required than to do it once your harness is fully taped. It is also wise to add a small amount of extra wire at the ends at this stage as well as it can be trimmed later.
At this point if possible I like to roughly lay the harness in position so I can check the lengths and trim it to its final length. You can now fit the terminals to the ends. Spade type terminals can be crimped with the crimping tool. Some ringlet terminals may need soldered as will bullet terminals. If you are using covers on your terminals or rubber sleeves, remember to push them onto the cable before fitting the terminals.
Now you are ready to tape your harness. Always start from an outside end and work towards a junction except on a very long run like the rear lights where doing this may end up in excess cable bunching up as you reach the middle. Hold the wiring firmly in one hand and wrap the tape around with the other, pulling tight to slightly stretch the tape as you pull it. Try to keep the tape as smooth as possible and overlap each turn by about one third. Taping wiring harnesses neatly is an acquired skill so don’t be surprised if you need to practice it a few times before you get the hang of it. When you get to a branch in the harness, tape past it a few centimetres and then break the tape and start at a new end point. Continue this until the harness is full taped and all the junctions look neat.
Well done! You now have a great looking (hopefully) wiring harness ready to fit back into place. If you have done all your measurements and checks properly then the harness should fit into place easily. Fit with new clips – why go to this bother and use cable ties? Reconnect your instruments and lights. Fit a new fuse box if you can and reconnect to regulators etc. Since you have now went to this level to get a good looking harness then why not replace your starter cable and earth straps as well?
(photos and wiring colouring to follow)