I am planning to add two rear fog lamps with a combined current draw of 0.66 amps at 13.2 volts, which translates to roughly 9 watts.

I can't really figure out how to run a wire from the trunk to the passenger compartment on my car (2012 IS350c). I know it's possible, but I can't really figure out the routing. I know I can poke around with a clothes hanger, but I have a better solution in mind anyway. Is this a realistic solution?

My solution is to keep a small, AGM lead-acid battery in the trunk, like a lawn-mower sized AGM battery. The battery will be secured in a corner of the trunk. The battery will power a relay, which will be connected to the rear fog lamps. I will use a wireless relay so I can hit a button in the passenger compartment and activate the relay in the trunk.

My questions are:

Is my plan realistic? Will it actually work?

What are some good sources of 12v wireless relays?

1 Answer 1


With such a small load ( 9W), you don’t have to use a relay, just pick up a suitable supply from the fusebox and run to the switch using a suitable fuse.

Running the cable to the rear is not to difficult - the existing wires are on one side(follow them from the back or in either footwell at the front), tucked under the carpet. Just lift up the door trims or unscrew them on the appropriate side.

If you do want to use a relay, then put it under the dash so you only need to take one wire to the rear.

  • Thank you for the advice. My wireless relay arrived today and it actually works quite well and requires no hard-wiring.
    – Dissenter
    Commented Apr 21, 2019 at 22:36

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