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Old 01-25-2005, 08:26 PM   #1
Scooby Newbie
Member#: 7347
Join Date: Jun 2001
Location: North Country, New York
2002 Impreza WRX
WR Blue

Question '02 WRX fog light wiring Qs...wire gauge, amperage, etc...

2 weeks ago both of my Hella 500 fogs quit working. Last week they're back from the dead. I made no changes to the sytem up till that point to explain why they stopped/started working again. Anyone else experience this?

As those Hellas were horribly cracked I replaced them with some Lightforce 170s with 100 watt bulbs. The vendor says that he uses them in his rally car using totally stock wiring with absolutely no problems. He believes the stock wiring is of a sufficient gauge to support the draw. I can get them to work for a couple of minutes or hours(depends on the day) before the 15 amp fuse blows. My calculations have each light drawing 8.3 amps, for a total of 16.6 amp. This is on the stock circuit's 15 amp fuse...that doesn't seem too good to me.

My Qs....
1) what gauge are the stock fog light wires?
2) can the wires handle 8 amps each, or 16 in total without melting?
3) can I assume that Subaru put wires in that would handle more current than the stock 4.5 amps each, or 9 amp total per side?
4) when the 15 amp fuse blows, I still have the switch's dashboard illumination, which I can understand...but the switch's "on" light still works. I figured that would go out with the blown fuse. Where is the "on" light getting it's juice from (which fuse)?
5) if the wiring does happen to be of a sufficient gauge to support the 16.6 amps, then would it be safe to pop in a 20 amp fuse?
6) when I mounted my old Hellas, I just connected them to the cars stock wiring, paying no attention to Subaru's switched grounds or whatever it is that makes them different from other vehicles. They worked fine for over 2 years that way. Is there some reason that I might need to switch my wiring plan (other than for problems with a possibly too-small gauge of wiring for the current draw)?
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Old 01-25-2005, 08:37 PM   #2
Trust no one
Member#: 11170
Join Date: Oct 2001
Chapter/Region: Tri-State
Location: NYC
02 WRX
15 WRX/05 GTO


The switch is only controlling the fog light relay, not the lights themselves. If the fuse for the lights blows the relay will still operate and so will the light in the switch.
I do not know the exact gauge of the wiring, but I would not recommend using any bulbs of higher wattage than the stock 55W. When a manufacturer fuses a circuit at a given amperage, it is never a good idea to install a higher rating fuse to allow for the purpose of running higher current on the circuit.
My suggestion, if you want to safely run 100W lights (and also to get the most output from them with minimal voltage drop), is to use the factory wiring to control a relay and power them directly from the battery.
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Old 01-25-2005, 09:56 PM   #3
Scooby Newbie
Member#: 7347
Join Date: Jun 2001
Location: North Country, New York
2002 Impreza WRX
WR Blue


Can I assume that I can use one set of original foglight wires to power the relay, with the other set from the other light just taped off? Are all relays rated for this current load? Can you recommend a commonly available one that will handle this load? What gauge wiring would you recommend on the fog light side of the relay (12, 14)? Would a 20 amp fuse be sufficient for the 16 plus amp draw, or will I need a 25( how much overage is typical)? You state that the original switch controls a relay...why would I need a second relay, and not just use the stocker?

Thanks in advance!
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