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Audi short circuit debugging lead

Audi ur-quattro and Type 44 Debugging Lead

General

This is a simple lead for debugging short circuits, especially designed for the ur-quattro's "Stephen" circuit.

"Stephen" is named after a famous rugby song - it is defined as being for "occasional current users" such as the horn, reversing lights, etc., and runs all over the car
Because of its omnipresence, a short in "Stephen" can be a bastard to fix - that and the black/blue colour of the wire give it its name
The lead consists of two connectors that replace a blade fuse in the fusebox and a 10A self-resetting thermal cutout - if there is a short in "Stephen" this contact breaker will repeatedly open the circuit and then reset itself
An LED on a long lead is connected across the contact breaker terminals - when the circuit opens, 12V is applied to the LED and it lights - when the cutout resets, it goes out
In use, the long lead is carried round the car while components are unplugged and wiring is checked - when the LED stops flashing, the fault has been found