Please educate me on Relays, Fuse, Wire Gauge and Switch for Fog Lights

Folks, please give me some information on Relays, Fuse, Wire Gauge and Switch for Fog Lights. I have an appointment with an installer this Monday to get a quote. The shop specialize in radio, speaker and TV installations on vehicles. But the owner of the shop said he has an installer that can install the lights, switches, relays, etc. I just want to have some idea on how this install should go. Here is what I have.

1. Relay - I was able to purchase a new set of 4 OEM Roof Mounted Off Road Lights (Part # 89006785). It only came with 1 harness (Off Road Lamp Harness - 4 male connectors used to attach the 4 lights. End of the wire have another SINGLE connector that have 3 female connector). Did not come with any other attachments. Zach was kind enough to copy the installation manual for the same Roof Lights for me. According to the manual, the "Body Harness" have 2 Relays ONLY. Though this set-up has "4 Lights".

I have another set (complete set) of OEM Grille Brush Guard Off Road (Part # 89006865). This kit only has "2 lights". Here is what I'm confused/concerned about. This set-up came with a "Body Harness" that also have "2 Relays".

So.... how can a 4-light set-up have 2 relays. And a 2-light set-up also 2 relays???

2. Fuse - for the 4 OEM Roof Mounted Off Road Lights, how should this be hooked up for fuse? Single fuse for all 4 lights? What Amp?

3. Wire Gauge - what gauge of wire is ideal for this?

4. Switch - the manual showed only one switch for all 4 lights.


I am also installing 2 sets of Hella FF75 lights up on the front roof rack, and a set on the rear. I think one switch for front and another one for the rear.

I am hoping the installer knows what to do when he see the truck this monday. I just want to have an idea on how to go on this install.

I hope to get some feedback from my fellow hummer owners. Thanks.

I have the oem bar on my h2.

Switch. All 4 lights are powered by 1 switch

Relay. It is just one relay for the whole bar.

Fuse. Since its one switch and one relay, it should only have 1 fuse built into the relay.

Hope this has been a helpful post.

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A bunch of questions there which are a bit situation-dependent so they are tough to answer right off the bat.

Lights - not exactly sure what you got there. Not sure of a 4 lamp OEM system. Can you post a pic or a link?

A relay basically handles the heavy power (amp) load that would overpower most switches. Most relays can handle 2-4 switches. Basically, the power to light the switches flows from the power source through the relay to the lights. The switch ties into the relay and opens/closes the circuit as necessary. It is normal to put 2 or 4 lights on one relay - it does not need to be one relay per light. Between the light(s) and the relay you would have Y branches separating the power to the lights.

Wire gauge is dependent on both length and power. There are calculators on the Internet to help with this. Likely you just need something like 18 gauge from switch to relay but 10-14 between relay and lights, and between lights and power source, depending on the amp draw of the lights. LEDs, for example, draw less power than traditional KCs. HIDs would fall in the middle.

I have four KCs on the front and those are on two different switches. On the roof I have three LED lights and those could easily be on one switch though I chose two switches. First, you have to figure out what you want and then build the system to match. More than likely you can do one switch for all four lights, and likely with only one relay.

Fuse amperage is determined by the lights. Once we have those specifics we can recommend fuses.

relays are just like sizing your cable & fuses... They have rating on how much power they can support. Your on/off switch is simply a remote control for the relay. All your "real" power flows from your power source, through the relay and to what ever you are powering- It doesn't flow through the switch. No matter how many relays you have, one switch can trigger them all.

Thanks to all who replied. Here are some pictures. Hopefully I can get some more instructions/informations.

Pic 1 & 2 - These are the lights that I got. The person I bought it from took them off from his roof light bar. It only came with 1 harness (Off Road Lamp Harness - 4 male connectors used to attach the 4 lights. End of the wire have another SINGLE connector that have 3 female connector). According to the installation manual (Pic #3), the kit comes with "1 Body Harness" (2 relays), which I don't have. See (Pic #4 &5).

Here is the part I got confused. On my other set of fog lights, OEM Grille Brush Guard Off Road (Part # 89006865), it only comes with 2 Fog Lights. But it also came with "1 Body Harness" (2 relays). See (Pic #6).




Pic #3


Pic # 4&5



Pic #6



So...
2 Fog Lights, 1 Body Harness with 2 Relays (Brush Guard Fog Lights)
4 Fog Lights, 1 Body Harness with 2 Relays (Roof Mounted Fog Lights)

Questions:
1. For my 4 Fog Lights on my brush guard, should I expect the installer to use 1 or 2 Relays???
2. What gauge wires should I expect him to use?
3. How about the fuse? How or where did you folks installed the fuse?
4. On the installation manual, they intructed on using the brake controller connection for the lights. I don't want to do that since I will be needing that when I tow a trailer. So I guess the installer will have to find a different way to run power on the lights.

I apologie for the lenghty post fellows. I tried my best to find someone who has an experinece in installing these lights on an H2. No luck. So I have to take chance on with a local shop. I just hope they do it PROPERLY as I don't want these lights to cause any fire.

Any instructions, suggestions or reminders will be greatly appreciated.

Fuse is installed as close to the power supply as possible. Run the power wire directly off the Batt + cable to the relay Pin 30 (as shown in Alrock's diagram. Battery is an excellent location for power). As for fuss size, unless I am missing something you have not stated the wattage of the bulbs used in each housing. Fuse size is determined by the draw from the bulb(s), same goes for the wire size; as well as length of wire needed.

1. For my 4 Fog Lights on my brush guard, should I expect the installer to use 1 or 2 Relays???
Could be either, depends a bit on the wattage of bulbs and how he chooses to do it.
2. What gauge wires should I expect him to use?
Depends on bulb wattage, see below
3. How about the fuse? How or where did you folks installed the fuse?
What F5 said
4. On the installation manual, they intructed on using the brake controller connection for the lights. I don't want to do that since I will be needing that when I tow a trailer. So I guess the installer will have to find a different way to run power on the lights.
You can run power from the battery, from the fuse block with an Add A Fuse, from a multitude of sources. He'll probably use the battery.


If I work under the assumption that each of those bulbs is 55 watts, then here's some math for you.

http://www.raylucke.com/20010926/tools/amps.phtml 4x55 watts, 12 volt system = 18 amps. That could be handled by one 30 amp relays. He may do two relays as it could be easier to keep track of the wiring.

Fuse would likely be a 30 amp fuse if one power source, or 15+ if one power source for each set of lights.

Wire sizes: http://www.gtsparkplugs.com/WireSizeCalc.html Size depends on length and amperage.