Circuit protection ,Circuit protection ,Circuit protection ,Circuit protection ,Circuit protection
You can not have enough!
Fuses and circuit breakers are your friend!

I will include an inline fuse with the stuff I send you.

My setup includes a main fuse from the battery to the main power block. Fuses for the individual items or circuit breakers notice them next to the toggle switches.

[quote=Ken White]Doc is correct, the fog amps should be wired in parallel with the 12V positive and the fog lamps should not pull power through the high-beam switch...

[/quote:3l780ioq]

They're pulling power through the low beams, the high beams are on the control side of the relay. The fogs are on the NC side and they receive power from the power provided for the low beams, which is a very bad idea on any vehicle made today.

Here's my setup:



But it could be even better if done this way:




But if you're doing a whole new circuit overlay instead, I'd suggest jumpering terminals 30 to 86 on the new relay if the installer wishes to add a switch, and use the switch leg on the pin 85 side of the relay to ground. This way there's no need to tap into the interior for power and no need to run a power wire through the firewall, the switch can work the ground side of the relay. It's safer, cheaper AND easier.

Like this:

Doc, its really irrelevent whether the power is pulled from the high beam or low beam side since the lights should not be powered through a switch that doesn't have its switch contact ratings sized correctly...

As for switching the ground side as shown in your Figure A, it is better to switch the hot wire since there will be less wire length having 12VDC applied to it when it is not switched to the on position which means there is less chance of accidently shorting a wire/terminal out when testing or during a failure mode... Put the switch on the other side of pins 30/86 and fuse it as near to the 12VDC (+) terminal as possible.

I had already agreed.

We can agree to disagree on this. The setup I posted can be located AT the battery, with ONE fuse and the trigger wire is safe unfused if done on the ground side. Then, a single 30A fused wire from battery to relay, short 1" jumper to the control side, and the output to the fogs is extremely simple and safe, the switch can be wired with 18ga and grounded to the dash bracket.

Switching the hot side requires a switch fuse and two "hot" wires...one 30A for the fog source and one 3A for the switch.

Doc, fuses are sized/used to protect the wiring insulation from melting if a short occurs. So even if you switch the ground, a smaller fuse should be used to ensure this larger gauge wiring is protected too. You can't rely on the coil in the relay to limit the current in the switch and wiring to a safe value - coils have been know to short across winding and contacts have been known to short across terminals...

You could also use one fuse if the same gauge wiring is used through out the installation...

I guess we will agree to disagree.

Have a Merry Christmas...

That was the idea, but I see your point!

The ground switching does shorten the length of the "live" wires though.

Merry Christmas!

True...