Weekend Workshop

Why rewiring your classic from scratch is surprisingly simple

We show you how to make your own wiring loom at home.

Is your classic car’s wiring a shambles? Does it conform to no electrical diagram known to man? Has it been ‘improved’ by a previous owner in ways that are entirely regrettable? Or is it a morass of insulation tape and those childish red, blue and yellow crimp terminals? As a general rule, we’d advise you to gently unpick unofficial additions until just the original loom is left. You can then make sure all the wires are going where they should and – if required – replace dodgy wires, connectors or components on an individual basis.

This should sort most problems.

In the case of looms that have been ruined by perishing, heat, chafing or butchery, however, it’s probably best to start again.

All the wires, terminals and tools are available via ebay or specialist suppliers, the latter tending to give better assurance that the stuff you’re buying is of decent quality. The process is pleasingly logical. Find the correct wiring diagram for your car. Use it to lay each wire from A to B, one at a time. Leave enough spare length to form the completed loom into bunched routes that follow sensible paths through the car. Fasten the new loom into position so it can’t flop down, fret against sharp edges or attack you while you’re driving, then do any final trimming. And that, in principle, is it.

Treat a loom as individual wires following defined routes rather than a terrifying maelstrom of copper tentacles, and you’ll never be overwhelmed by it. It’s a better solution than trying to reproduce the old loom – defects and all – on the bench and then force-feeding it into the bodyshell.

You will need Wire, terminals and connectors, crimping tools, wire cutters and strippers, insulation tape, loom tape, heat-shrink, P-clips or other fixings. Use your diagram Work to the original diagram and note any alterations. When you’ve finished, produce a ‘master’ diagram that clearly shows changes in wire colour or electrical equipment. Wire ratings The wire sizes given in the feature are suggestions only. If in doubt, check your manual or work them out carefully. Tidy wiring Temporarily bind wires together with a band of tape as you go. It’ll help with routing and length estimates.