A replacement wiring loom is one of the most significant purchases an owner can make during a restoration, as the loom connects every electrical component on the car and its condition affects the reliability of the entire electrical system. Each Midget loom is specific to a narrow production date range, sometimes covering only a single model year, reflecting the constant changes to switches, instruments, lighting, and ancillaries that occurred throughout production. The exact chassis number must be quoted when ordering, as looms are not interchangeable between adjacent production periods.
Harness Layout
The loom typically consists of three separate harnesses: the main harness (running from the fuse box through the bulkhead to the dashboard instruments and switches), the front sub-harness (serving the headlamps, indicators, side lights, and horn), and the rear sub-harness (serving the tail lights, number plate lamp, fuel pump, and fuel gauge sender). Each harness must be matched to the car's chassis number to ensure the correct connector types, wire colours, and circuit routing are supplied.
Loom Finishes
Looms are available in two finishes: modern PVC-bound, which is durable and practical for a car in regular use, and period-correct braided cotton-bound for earlier cars where concours authenticity is the priority. The braided cotton loom uses the same wire colours and connector types as the PVC version but is wrapped in woven cotton sleeving that replicates the original factory appearance. The choice between the two is purely aesthetic and practical, the electrical function is identical.
Bulkhead Grommets and Plugs
The bulkhead grommets seal the points where the wiring harness, wiper rack, heater cable, choke cable, and other items pass through the bulkhead. A grommet seals the gap between the hole and the item passing through it, preventing water ingress and stopping the wire insulation from chafing on the sharp metal edge of the hole. A plug blanks off an unused hole entirely.
These items perish over time and should be renewed whenever the loom is replaced, aged grommets are a common source of water leaks into the footwell and engine fumes entering the cabin, both of which are easily resolved with a complete grommet and plug set.
Fitting a New Loom
When fitting a new loom, the old loom should be retained as a reference throughout the process. Each connection should be transferred one at a time from old to new, verifying the routing through grommets and clips at each stage. The loom should be routed away from heat sources, particularly the exhaust manifold, and secured by clips at all the original mounting points. A wiring diagram specific to the car's production date is invaluable during the work.
Incorrect routing can result in wires chafing on sharp edges, melting on hot exhaust components, or being trapped by moving parts, any of which can cause a short circuit and potentially a fire. Taking photographs of the old loom's routing before removal provides an additional reference that a wiring diagram alone cannot always convey.