hi anybody help i have been building for a long while and have a griffin power systems bike loom,i have just found out that iva regs state that the, rear fog light cannot work with the side lights on ,just the main and dip beam ,i have spliced in to the dip and main beam relays outcomeing wires and run these to the fog switch this worked great on there own but when twisted together i have a dead short and i blow the headlight fuse i have now realized that i am sending 12 volts back up to the realays ,ie if iswitch on dip beam this has 12 volts and nothing on the main beam, then when i switch main beam i get the reverse ,but because i have twisted these together dead short ,how as everyone else got over this any help PLEASE, bloody electrics.

For me, I would only supply the rear fog from the dipped beam circuit; if it's clear enough to drive with full beam on without you being blinded by back scatter, you shouldn't have your rear fog on anyway as you will be blinding following drivers.

However if you must, you can use two relays, the coil of each (85-86) operated separately by the dip and main beam circuits (connect dip/main power to 85, 86 to earth). Then the relays' switched circuits (30-87) are both parallel fed by a fused ignition live to feed power to your rear fog switch and thence to your rear fog light(s).

A neater way again is to use a single relay, terminal 85 powered via 1N4002/3/4 diodes to the dip and main beam circuits (so you then can't back-feed 12V between the two circuits), terminal 86 is connected via your rear fog switch to earth. Then the relay's switched circuit (30-87) feeds your rear fog lights from a fused ignition feed. of course if you enable the fog from the dipped beam only, there's no need for diodes. Using the relay this way means your rear fog switch only has to handle the relay coil current rather than the full fog light current, which is a good thing.

If you do want to use diodes in car wiring, you need to mount them such that their leads aren't subject to movement/vibration. You can solder them directly into a wire and use a couple of glued shrink wrap tubes to ruggedise the assembly. Or you can mount them in in-line fuse holders (bend the leads to mimic a blade fuse and ease them into the holders). Or use a piece of veroboard to mount the diodes.

Cheers R

This is how I did it with Sierra stalks and a Premier wiring loom. Basically its set up so that you only get power to the fog relay solenoid when the headlight switch and the fog light switch are on (note that this is a switched earth set up, so the only path to earth is via the headlight switch)...