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wire/relay question


NAXJA Forum User
98 XJ Limited.
Does the factory fog light switch kick on the relay, or does the relay supply power to the switch?
I'm trying to determine if the switch can handle the fog light current running through it.

See, I got a custom bumper the other day and I decided to relocate and wire the fog lights as auxiliary back up lights.
I can't figure out where to tap for power and I don't want to fry the switch running power through there. Thanks.
Switches turn on relays. The relay contacts can switch a lot of current; however, a light duty switch can energize the relay. It's the relay that you're interested in as well as the wiring and the fuse.
Ok, so I would normally agree with that logic, however... When I test the system this is what I found. There is a power wire to the relay that is always on (battery power I assume), the other 3 wires are dead. When I turn the headlights on, fog lamp switch off, the purple wire on the relay becomes power. This is the same color wire as the power wire into the fog light switch. The fog light switch has no affect on the fog lamp relay, either on or off. From more testing we determined that the power coming out of the fog light switch was light blue, the same color as the hot lead on the fog lamps themselves. So to me, this means that the power comes from the headlamp switch, turns the relay on and the relay provides power to the switch and the switch to the fog lights. One last thing I noticed was if I pull the fog lamp relay there is no longer any power to the fog lamp switch.

Strange I know, this also seems to go against the Haynes manual.
My newest FSM is '93 and shows wires of a different color. My Haynes seems to show two configurations for fog light wiring. One of them uses a single relay and the other one uses two. For the single relay scheme it looks like what you are describing and the relay looks like it's there to make it possible to turn on the fogs only when the headlights are on. It looks like the dash switch really does directly switch the power for the fogs.
Into the relay (four wires are all that is really necessary) you will have one line "always hot" (either "hot at all times" or "hot in run" - probably the latter,) two more hot with the switch on (one low-current from the switch, and one passing power to the device,) and one ground (the other side of the switched poles.) If you look at the relay, you will see a coil symbol - one side of that will be grounded and the other will run to the switch. Sometimes, the switch is in the ground side, but I think our XJs all have hot-side switches. The other side will show two fixed contacts and one movable. The picture will show the centre contact will be shown touching one of the sides - that side will likely not be wired. The centre and the other side will be wired for power and load. One of these two will be hot - either direct from battery or from ignition. It is pretty common for the centre contact to be wired hot.

I don't have the contact numbers handy, but they should be on the relay as well.
Don't forget that when dealing with factory fog lights they are wired to automatically go off when you switch the headlights to high beam. Be certain you are tracing your circuits and testing contacts with the headlights on low beam.

The '97+ are wired so the fogs operate with parking lights only, which means they must have a second normally-closed relay in the circuit that opens when the high beams are energized. I don't think the older ones are wired the same way, so year makes a difference. (As usual)

You can easily test to see if power comes to the switch through the relay -- check switch input for power. When you get power, then pull the relay and see if the power goes away. However, if there are two relays, as I suspect, be sure you have the relay that turns the lights on, not the relay that turns the lights off.

My '98 wired as per factory schematic allows the fogs to come on with the low beams too as well as with the parking lts. Was this an oversight?
Re: Eagle-

Judd W. VA said:
My '98 wired as per factory schematic allows the fogs to come on with the low beams too as well as with the parking lts. Was this an oversight?

No, my 2000 is wired the same way. However, this requires an extra relay. If the fogs are wired with the switch tapped off the low beams, they will automatically go off when you hit the high beams, but they won't work if you only turn on the parking lights.

However, if you tap the parking light circuit to run the control wire through the fog light switch, then the fog light relay doesn't know if the headlights are on high beam or low beam. The usual solution is to run the light power circuit through a second relay that is "normally closed" (on), and which turns OFF when the high beams are energized. Is that what your schematic shows?