The MG Wiring Colour Code

A guide to the wiring colour codes of the MG sportscar by Barrie Jones.

The automotive wiring colour code that we know today was invented around 1936. I believe the company that invented and maintained it was Ripaults, not Lucas. Ripaults Cables Ltd is a long-established manufacturer of automotive cable and wiring looms in the UK.

The Ripaults colour code quickly became the de facto standard in the UK. Each colour was denoted by a unique letter, and some letters were reserved for other purposes. MG did follow the colour code, but unfortunately they did not use the letters on their wiring diagrams until 1962, staying with an earlier system where the wiring diagram used numbers and a cross-reference table was required.

Different codes were followed in other countries, and many cars sold in the UK used the German code, particularly VW. Ford cars could have either UK or German looms, depending on where they were built.

The only significant change to the colour code was around 1955, when the primary colour Yellow was changed to Brown. Secondary colours were not changed at that time, so Yellow with a Red stripe became Brown with a Red stripe, etc. The special cases were:

• Plain Yellow became Brown with a Yellow stripe, and
• Yellow with a Brown stripe became plain Brown.

MG continued to use Yellow on the TF and all the MGAs, only changing to Brown when they introduced the MGB in 1962.

At some time, the primary colour of Purple was introduced for those wires that were fused (A1-A2) and permanently live (e.g. the horn circuit). The timing of this change is unclear, because some TDs used the new colour code, although the TF and the MGA did not.

Since then, new colours have been added to the system, notably Light Green (LG), Slate grey (S), Pink (K) and Orange (O). There is one light green wire in the TF loom. I assume that Ripaults chose S for Slate grey because they had already used G, R, E and Y.

The first table (following) shows the meaning of the primary colour. For example, all white wires are part of the ignition circuit, they are not fused, and they are switched via the ignition switch

Primary Colour Code

* some brown wires are fused prior to the introduction of purple

The second table (following) shows most of the wires in the TF loom, including those with a stripe. For example, the wire between the distributor and the coil should be white with a black stripe, coded WB.

Full Colour Code (TF)

* I know they are white, but logically they should have been green

Full Colour Code (TC and TD)

* Some TD looms used purple, most used brown

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