Pre-war Wiring

Pre-war Wiring

The majority of the wiring fitted to pre-war chassis consisted of a multi-strand copper conductor surrounded by an insulating sleeve of natural rubber. This was covered with a braided cotton sheath which was coloured for identification purposes. Including the battery cable there were typically five different sizes of cable, whichever was specified depending upon the expected current in that particular conductor.

Over a long period of time the integrity of the rubber insulation can suffer badly from the effects of aging. Left to its own devices the rubber will tend to harden and become brittle, particularly where it has been exposed to the atmosphere. If moved or disturbed the insulation on cables in this condition will easily crack and fall away, leaving exposed and unprotected conductors.

Conversely, another property of natural rubber is that when exposed to oil and petrol, or even their fumes, they will be absorbed by the rubber. This causes the rubber to soften, and ultimately it will be converted to a near-fluid condition. We have found original wiring, particularly on the engine firewall or bulkhead, in which the separate conductors are effectively swimming in a rubber goo, and they are no longer being kept separate.

In the early stages of wiring failure small growths can be seen on the outside of the insulation. These originate at defects or minor perforations in the covering.

Other than in very exceptional circumstances it is almost certain that the wiring fitted to a pre-war vehicle, if original, has the potential at the least of a small fire-work display, and at worst a major conflagration. We know of several cars that have apparently self-combusted, the problem originating in defective electrical systems. Before this point is reached there can be a period of extreme unreliability, for no obvious reason. Do not forget that when investigating such problems they can be made worse by moving and disturbing the wiring.

Even in the case of an otherwise totally original car the wisdom of not renewing the wiring is questionable. Once a car starts to burn, the timber-framed coachwork, very well seasoned and probably extremely dry, with plenty of aluminium and extremely combustible fuel, make a lethal combination. Rewiring a car using modern materials can be better than any insurance policy - you should not have to make a claim.

Modern wiring uses PVC as the insulation, which does not age in the same way as rubber. Automotive PVC-covered cable is very efficient, but anachronistic in a pre-war car. The cable which we supply and regularly use when rewiring a chassis is visually very similar to the original, being cotton covered.

The conductors are covered with a thin but high quality layer of PVC, and this is sheathed in a cotton covering similar to the original, which has a clear lacquer to stop the cotton from fraying. In general the colours that we supply are similar to those on the original wiring diagram. However, to assist with the identification of certain cables and later trouble-shooting we have found it advantageous to add a second colour to some cables. These changes can be removed if required, and all-original colours supplied. The only difference will be in the blue; two shades of blue were specified by Rolls-Royce for the ignition, brake light and horn circuits. At this time only one shade of blue cotton covering is available.

We can supply a Wiring List for most pre-war Rolls-Royce and Derby Bentley chassis. This will list the individual cables for each function, giving the size of cable and colour. We welcome your enquiries; please let us have your Chassis Number to enable us to prepare the correct Wiring List for your vehicle.