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One satisfying task in the progression of restoring a car is the installation of a new wiring harness in the freshly painted body. It is really not a very difficult task to put a new wiring harness in an MGA. There is a point when you should do this – after all the painting and some of the ancillary pieces are installed, but before you have too much clutter or pieces blocking the harness run. For the MGA, a really nice wiring harnesses, with modern insulated wires inside period cloth covering, is available from Moss Motors. These typically have the connections you will need and the bulb holders for the instrument panel lighting bulbs. There are many grommets on the MGA bulkhead – and to make your life simpler you can purchase a kit will all the different assorted ones. Figure on spending more than $50 US on that. I like to use stainless steel fasteners and p-clips as well. Keeps things looking new forever.

A nice thing about rewiring the MGA is that the harness is in multiple pieces with a big bunch of connectors just above the starter on the inner wheel well. This makes it simple because you can wire the bulkhead and all the important bits like the control box, flasher system, fuses and windscreen washer with one part of the harness. Then run the harness to the headlamps and front indicators and the rear harness to the tail lights and fuel gauge. The best part is that the dash has a separate harness, so you can wire all the instruments and switches etc up on the bench, connect to the main harness when installing the dash.

Below are some pictures of installing a new wiring harness in a 1958 MGA –

A colour wiring diagram is useful and some protection for the new paintwork is good when installing a wiring harness in the MGA. Note bag of assorted grommets. You need a lot of all different types.
A new MGA wiring harness with the bulb holders already attached.
I like to use stainless fasteners and p-clips for the wiring harness. May not be original – but looks and wears great.
Two sections of the MGA wiring harness run under the brake/clutch master cylinder support and to the windscreen wiper motor and down through a grommeted hole in heater shelf to the headlamp dimmer switch.
MGA headlamp dimmer switch is connected by a wiring harness section that runs down to it from the heater shelf.
MGA wiring harness running forward to the horns, headlamps and indicators along the inner fender. It is held by p-clips. It then runs underneath the support that has the bonnet locking mechanism. Connectors to the lamps and horns are inside on each side of the nose. You can see one side here.
On the lift for this part. The MGA wiring harness to the rear lights and the fuel indicator runs along the chassis along with the power cable from the battery. I replaced my worn battery cable with a new one. They are held together with double curved p-clips.
On the MGA there is a mass of connectors for the various wiring harness bits near the starter solenoid, just above the starter. The battery line runs up to the solenoid and the power for the starter and the rest of the car is linked-up there.
There is a separate sub-harness to wire the MGA dash. This makes it nice because you wire all the lights, the fuel gauge and the switches on the bench and then install the dash in the car ready-wired.
Having a continuity tester to check all is good is not a bad idea.
Installing the wiring harness in a 1958 MGA – very pleasant work indeed!
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