Switch/Relay help - JeepForum.com
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post #1 of 3 Old 10-05-2011, 11:25 PM Thread Starter
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2006 WK 
Join Date: Apr 2009
Location: Nampa, ID
Posts: 548
Switch/Relay help

I'm eventually going to wire my up my fogs that I got for my birthday in May, just haven't got around to it. They are just cheap walmart lights, 55w bulbs, but probably going to put something like 100w bulbs in. I am looking to wire them myself, as the wiring it came with doesn't include relay and has a cheap switch. I am looking to use a Carling rocker type switch.

This is where I am confused. When purchasing a switch, do I want a SPST or SPDT switch? Same goes with the relay; SPST or SPDT? I want to get this right the first time, and I'm sure some know what is best. Any takers?

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post #2 of 3 Old 10-06-2011, 05:42 AM
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For a basic fog lamp circuit, all you will need are a SPST ON-OFF (not momentary) switch and a SPST relay. (Most, if not all automotive relays are SPST or SPDT.)

I may want to talk you out of the 100W bulbs since a cheap fog lamp housing may not be able to handle the additional heat. If you do end up going the 100W route, you will also need to upgrade the wiring to 12 gauge or 10 gauge on the power and ground leads directly for the lamps.

Switch Types:

Relay Types:

(A typical 30Amp ISO/Mini-Relay w/ Mounting Tab shown above. Commonly called a "Bosch relay."

Anyone of the relay types above will do. The 'single-87' (SPST) and '87-87A' (SPDT) terminal relays are the most common. If you can locate a 'dual-87' (SPST) terminal relay as shown in the first pin-view diagram above would be a bonus. The 'dual-87' terminal configuration just makes wiring two lamps a little easier and cleaner. Nothing else.

Typical Fog/Driving Lamp schematic:

Another representation:

(87A terminal, center, not used)

4.0L TJ
Slithering_Joe is offline  
post #3 of 3 Old 10-06-2011, 10:24 AM Thread Starter
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Join Date: Apr 2009
Location: Nampa, ID
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Wow. Thank you for all that information! That will help me a lot! As far as the bulb wattage, the housing is metal and has glass lenses, is it wrong for me to assume I will be ok with higher wattage bulbs? I know if I do that, I will need larger gauge wire, but that wont be a problem (just a little more expensive)

Again, thank you Slithering_Joe. It's members like you that make this forum an awesome place!
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