by Jim Slostad, Cascade Austin-Healey Club

Here's how to set up Concours-approved front-mounted driving or fog lights.

You'll need the following:

  • An SB40 overdrive relay
  • A wiper-motor switch
  • Four to six feet of 18 gauge wire (solid red)
  • 10 to 12 feet of 18 gauge wire (red with yellow stripe)
  • Six to eight feet of solid brown 14-gauge wire
  • Ten-12 feet of 14-gauge wire (brown with red stripe)
  • Eight to ten feet of solid black 14-gauge wire
  • Eight to ten feet of solid black 3/8" or 5/16" cloth  harness.

Alternate wire colors are yellow/black instead of red/yellow and black/red instead of brown/red.
Sand the word "wiper" off the switch knob and replace with "L" for "LIGHT' or "F" for "FOG."
Other marques used this same switch and you may Find one with a knob that says "L", "F' or "AUX."
(MGAs used "F" switches—ed.) They will also be acceptable. Toggle or other switches will not be
acceptable unless mounted under the dash. Run solid red wire from the parking light terminal of the
lighting switch (terminal SI) to the on-off switch. Run red with yellow stripe wire from the switch,
through the firewall to terminal Wl of the SB40 relay. Solid brown 14-gauge write goes from
power source at fuse terminal A I to the relay at terminal Cl. Attach this wire alongside the factory
wiring harness.

Connect a length of brown wire with red strip from relay contract C2 to the lights as shown in
figure I. Attach this wire alongside the harness also. Use solid black wire for ground connections
to lights.

Note three things:


  • Wires outside the engine compartment should be routed inside the solid black cloth harness
  • Wires inside the compartment may be routed loosely or harness through standard wire harness clamps
  • The colors do not conflict with or duplicate other wires found standard in main factory wiring harnesses. (A deviation from these ecommended colors that accomplishes the same end will be accepted.)

ImageShould anyone be able to produce an authentic factory wiring diagram showing an installation other than this, please be advised that the oncours Committee would welcome it and consider it for adoption. (This article was taken from Cascade, the
official publication of the Cascade Austin-Healey Club. Figure 2 shows an alternative lighting ircuit supplied by Sean Johnson, editor of Cascade.  Johnson's circuit was taken from two ealer-fitted cars he looked at, and is set up so the switch acts only as a ground interrupt. One other ifference: In Johnson '.i circuit, the auxiliary lights will operate only if the headlights are. on.
Please note, however, that by attaching the circuit to the. blue line. of the dimmer switch as hown in Johnson's circuit, the auxiliary lights will operate if either high beams or low beams are sed. Sean says that's OK in Washington State, but my understanding is that in California you cannot run high beams and. auxiliary lights together. To automatically turn the. auxiliary lights ff whenever the high beams are used, draw power off the low beam line (blue/red) at the dip switch
as shown in the diagram, rather than from the power-in (blue) line.

Figure 1: System described by Jim Slostad, uses SR40 relay to take current from  fuse terminal Al through relays
to lights, lessening current load on switch.

Austin-Healey Magazine, July 1994   17