Help

GMCSierraSLE1500 · May 18, 2009

I have a pair of aftermarket fog lights on my bull bar for temporary till I determine what driving light I want, I noticed last night that the white wire(powers the switches illumination) is all melted and blackened(as if it had a fire) then I noticed the power wire(red) all melted(the rubber sheath) does anyone have an idea what is or what may be causing this because no other light i've owned has done this. These are a pair of POS fog lights that I picked up from Wal-Mart till I find the correct sized driving light for the bull bar.

mfennema · May 18, 2009

Are you running all of the amperage through the switch that is running the lights? You should only be using this switch to switch a relay and the relay should be powering the lights. Do you have a schematic of how you are running these lights? Or are you just using the wiring that was there originally for the OEM fogs? More info about the setup is needed.

bill190 · May 18, 2009

Use a 50 amp capacity DC amp meter (ammeter/multimeter) to measure the amperage draw of the lights when connected to a battery.

Then install the correct wire size for the amperage needed as well as a fuse of the correct size for the circuit.

Generally the load on any circuit should only be 80% of the circuit and fuse capacity. This means EVERYTHING on that circuit turned on at the same time.

For example, if something is drawing 16 amps, the fuse and wiring should be 20 amp capacity.

Wire gauge sizes for 12V wiring

22 - 5A

20 - 8A

18 - 10A

16 - 20A

14 - 40A

12 - 60A

10 - 100A

8 - 150A

GMCSierraSLE1500 · May 18, 2009

Are you running all of the amperage through the switch that is running the lights? You should only be using this switch to switch a relay and the relay should be powering the lights. Do you have a schematic of how you are running these lights? Or are you just using the wiring that was there originally for the OEM fogs? More info about the setup is needed.

These are not OEM fog lights, these are aftermarket fog lights that I picked up to put on my bull bar for temporary and when I got these they did not come with a relay that I am aware of, it had the wiring from the lights, an inline fuse and wiring to the switch, other then that it's unknown, now is this a problem that should be worried or just left go because the last pair(same company) which were driving lights when I had my brush guard came with an relay but this set did not so if anything was to happen would it not be the companies fault as I would be using what is supplied, when I called customer service they never stated anything about a relay so I left it go figuring it wasnt needed.

mfennema · May 18, 2009

If the lights are pulling more amperage than the switch is rated for, you should be running power to them through a relay. That way the only power that is going through the switch is signal power and won't melt the switch down. As bill190 stated, make sure that you use the proper wire size when wiring from the battery to a fuse to the relay to the lights as this will have all of the current running through it and you don't want the wire to melt down like is your case now. You can then run a smaller wire from the battery (or other power source) to the switch to the switching post of the relay as this wire does not carry much current at all.

In my opinion, even though you didn't get the relay with the lights, I would still install one. (Can't help ya on who would be responsible if something happened because there was supposed to be a relay and there wasn't one in the system.)

Relays are cheap and you can get them from AutoZone

bill190 · May 18, 2009

Generally the idea of using a relay is so you can keep all the big wires under the hood, run smaller wires into the car, and use a small low amperage switch in the car.

A relay is just an electric switch which draws very little amperage to operate, yet can switch higher amperage devices.

For example the starter needs BIG wires to make it operate. Imagine running those big wires into the steering column and connecting them to the key switch! Instead they use a starter relay or solenoid to the high amperage switching under the hood at the starter. Then can run low amperage wires to the key switch. The key switch just activates the lower amperage starter relay or solenoid.

And it is common to do the same thing with headlights and fog lights. You can run the switch and relay off of an existing circuit inside the car, but connect the higher amperage relay contacts connection and power to the lights on a fused circuit off the battery, then don't need to worry about overloading an inside fuse/circuit.