[Walt Fricke]

Well, you also said you are using a relay. The purpose of the relay is to allow a small current (=smaller wire and, if used, smaller fuse) to send a larger current to the actual device (in this case, a pair of fog light bulbs I suppose).

That poses a question: do you fuse the control circuit, the power circuit, or both. I don't know what the consensus of EEs is. I tend to want a fuse to protect just about everything, in case a wire creates a short, so I'd fuse the control circuit positive wire at or close to the fuse box (or the stereo switched power, if that is located conveniently or is simply one you know you can locate), just in case it gets shorted. Porsche grabs it from a headlamp circuit, I think (partly so you can't have the high beams and the fogs on at the same time, but I forget some of this).

And I'd do the same for the power circuit which runs from the fuse box or somewhere (it could come direct from the battery positive, for that matter) to the relay.

How big? Well, you could use a pretty small fuse - 8 amps would be more than enough - for the switch circuit. As to wire size, look at the wires to the instrument lights. Those are plenty big enough for this task, and for the indicator light bulb as well.

The power circuit? Look at the wires which go to the headlamps. Those are thought to be marginal for their job, but should be fine for your fog lights. Get some that size. And fuses? Well, you could experiment - put in an 8 and see if it blows. A 16 ought to be enough, I'm wildly guessing.

Want to be more accurate? Well, you can can pretty easily calculate the power draw. Somewhere you can find how many watts your fog light bulbs are rated for. Let's say each says 60 watts, so you have 120 watts. At 12 volts, that means the pair are drawing 10 amps. The wires will draw a bit more all on their own, as they have some resistance, but you'd be fine with a 16 amp fuse in this example.

Hooking up your indicator light bulb? Simple. The switch has an in and an out. Run a second wire from the out side (the one that heads off to the relay) to the bulb. I'd crimp that wire into the same connector as the wire to the relay, though it would be quite short. It looks like the switch body is grounded, but if you find your bulb doesn't work, connect some metal part of the switch to a ground to see if that makes it come on and then improve the switch grounding.

Some of this I think you can, after Randy's help, dope out from the diagram that came with all this. I deduce from it that the wire to the switch with the circle with an X inside indicates a switched power source. And there is no particular reason to choose one or the other of the two top spade lugs for the "in" side of the switch, which is just a single pole single throw (on or off) switch I imagine. Whichever one you chose is the in, the other the out. It only depends on where the wires come from or go.

If no relay is involved, you just need biggish wire for everything, but you still want the fuse as close to the source of 12V+ as you can reasonable get it. Blown fuses are not a big deal, but fried melted wires from a short can be, and at a minimum often melt and mess up more important wires.

I don't have giant stereos, so the wires to my radios are pretty puny. Not big enough at all to power fog lights (though they should handle relays and indicators). If there is no relay, I'd not start by thinking of stereos.

Maybe some real wire guy will check in with wire gauges and actual fog lamp wattages and such. You may want to buy wires at a store using specs instead of just looking in your spare wire box for something long enough and thick enough by eyeball as I would. Porsche wires are specified by their thickness in millimeters, not in the "gauges" that US wires tend to come in.

Walt