Mystery purple wire

I've been getting my head around all the wiring circuits in my TC2500. There are three fuses, each of which supplies a separate group of things. BUT there is a mystery purple wire going from the headlight switch to another group of things (horn, clock, courtesy lights). What is the point of this wire?

I am not 100% sure, but I will throw this out. . . .

On the TR6's it appears that the purple wire is a round about way of getting power to the lamp switch when the ignition is off. Begining at the starter, there is a brown wire that feeds the fuse block (FB), on the load side of the FB this wire becomes purple and feeds the horn, interior courtesy lights, glove box lamp and boot lamp. It also connects to the light switch.

I am guessing that the brown wire goes 'dead' after the alternator is up to speed as the white w/red wire from the ignition switch to the lamp switch is not energized until the ignition circuit is turned on. Like I said, just a guess. . . . .

I'm not familiar with the TC2500, but assuming it's like all other Triumphs (and most other British cars as well), the purple wire you mention is for the "flash-to-pass" feature of the headlight switch.

British cars all follow a very similar color code. The main power wires and colors are:

BROWN wires are hot all the time and are NOT fused.

WHITE wires are hot only when the key is on, and are NOT fused.

PURPLE wires are hot all the time, and ARE fused.

GREEN wires are hot only when the key is on, and ARE fused.

The flash-to-pass function is wired hot all the time so you can use the lights as a warning function if needed, even if you don't have the key in the switch. Same is true of the horns. If someone is backing into you, you won't have time to put the key in before the bang!

Hello Wombat,
yes, Danmas is quite right and Don is also in his first paragraph. There is, however, no link between the lights and the ignition, as they are available whether the ignition is on or off. However, Don, the brown wire never goes dead and the white red wire is the ignition switch to starter solenoid. When you turn the ignition switch to start, this wire is live and energises the starter solenoid.

Alec

Excellent, thanks! And the standard colours are very useful to know.

I believe there is a good list of the "general" Lucas wire color codes at www.britishwiring.com On the cars I have, the light gauge purple wires were for the dome/courtesy light while heavy gauge purple wires were part of the horn circuit.