Fog light switch question

joetiii · joetiii's Garage

So I'm hooking up my foglights and I'm wondering I can use my rear defrost switch for on/off. Now that the switch is useless since wiring did not go back in during restoration, I wonder if this pull knob can be used? Hmmmm

70SATMan · 03-10-2007, 04:16 PM

Yes it can Joe. It's essentially the same switch as the fog light switch.

mjshira · 03-10-2007, 04:53 PM

just don't use it to switch two things or you'll over load it. I would also suggest that you add a fuse to that power circuit so that you have added insurance.

911pcars · 03-10-2007, 08:30 PM

Suggest using the switch to energize a relay that actually provides source voltage to the fog lights. The relays result in less voltage drop (brighter lights) and saves wear and tear on the switch (just like the add-on relays for the headlight circuit).

Sherwood

joetiii · joetiii's Garage

Quote:

Originally posted by 911pcars
Suggest using the switch to energize a relay that actually provides source voltage to the fog lights. The relays result in less voltage drop (brighter lights) and saves wear and tear on the switch (just like the add-on relays for the headlight circuit).

Sherwood

I am definitely using a relay for this as the bulbs themselves are 100 watt and I'm sure they would toast the old wiring and switch. I imagine std 18 guage new wire to be acceptable.

70SATMan · 03-11-2007, 08:02 AM

100W fogs? Dang!

I'm running H1 fogs at 55W.

16 AWG minimum! on the lines to the relay. Bump up the grounds too. The original Porsche under bumper fog wiring to the relay panels only saw a maximum of 35W H3s. The thru the grill wiring saw as much as the Italian H1s 55W driving lights.

joetiii · joetiii's Garage

Quote:

Originally posted by 70SATMan
100W fogs? Dang! I'm running H1 fogs at 55W.

16 AWG minimum! on the lines to the relay. Bump up the grounds too. The original Porsche under bumper fog wiring to the relay panels only saw a maximum of 35W H3s. The thru the grill wiring saw as much as the Italian H1s 55W driving lights.

My mistake... they're not fogs but rather thru grill driving lights and they're 1000 watts per light.

911pcars · 03-11-2007, 01:05 PM

"My mistake... they're not fogs but rather thru grill driving lights and they're 1000 watts per light."

Errr, or was that 100 watts/light?

At 1000 watts, you'd need at least no. 4 cable (almost a battery cable), but I think you meant 100 watts.

In that case, the charts recommend 12 gauge wire for the power side (from source voltage to lights). But that's per light. The control side (source-to-relay-to-switch) is okay using 18 gauge wire. If you use one relay, make sure it has the current capacity for two-100 watt lamps (25A-rated relay will do). You can also build a circuit with one relay per lamp in case one relay or fuse fails. It depends on how dark it is, how fast you're traveling and thus how much light will suffice.

Sherwood

70SATMan · 03-11-2007, 07:39 PM

Quote:

Originally posted by 911pcars
In that case, the charts recommend 12 gauge wire for the power side (from source voltage to lights). But that's per light.
Sherwood

Yep, Sherwood is right. My mistake.

Note to myself: Michael, repeat after me...When working on my car Think Low voltage circuit, THink Low voltage circuit..

Much more critical in the 12V circuit. It's not really a matter of the amperage here and what the wire can handle. It's the % voltage drop in the wire really and what that does to the overall light output by the time you reach the bulbs. Even though we're talking about what? Say less than 10 ft to the far foglight? Wait, that's on my 70. Your 69 will have the relays further up near the cowl?

joetiii · joetiii's Garage

Quote:

Originally posted by 70SATMan
It's not really a matter of the amperage here and what the wire can handle. It's the % voltage drop in the wire really and what that does to the overall light output by the time you reach the bulbs. Even though we're talking about what? Say less than 10 ft to the far foglight? Wait, that's on my 70. Your 69 will have the relays further up near the cowl?

I have relays up inside the cowl but have replaced them with new ones when I installed the H4s. I have a new relay and fuse for the driving lights that will be going in.

Not sure how noticeable a drop in power will be on 10000 watt bulbs.