Hi guys, got a little 55W driving light that I want to use as an extra reversing light. Have worked out where I will mount it, but was wondering about the wiring... Can I just add it to the existing circuit without overloading it, or will I have to wire it on its own circuit? If I have to do the latter, how would I do so and what would it require?

Thanks.

55W will be drawing 4.5A. I'm not sure what the existing reversing lights draw but if you can work that out, then add the current they draw to the 4.5A. If the total is larger than the fuse, then you have 2 options.

If the wire guage is thick enough, you might be able to increase the fuse current rating to suit but you better be sure otherwise you might start a fire.

The other safer option is to run its own circuit. Go to jaycar and get a relay to suit, get wire with a current rating higher than 4.5A and an inline fuse with a lower current rating than the wire. Run from the positive side of the battery with the fuse first (close to the battery), then too the relay common side. Then from the normally open pin of the relay to the +ve of the lamp. Then from the negative of the lamp to a good grounding point.

Run a cable from the reversing light relay coil to the coil of your new relay, and then the other side of the coil to an earthing point.

What model car ?? (e.g. EA-EL).
What is the body type ?? (sedan/wagon/ute)
Do want a switch, or do you want the light to go on/off with the reverse lights ??

thanks for your replies
its an ef falcon gli sedan
does anyone know the draw of existing reversing lights and the rating of the cable
i just want it to come on/off with existing lights

Reverse lts are 2 x 5 watt IIRC. I'd say the wire would be 10A max. The main issue would be whether the inhibitor switch reverse switch would handle the extra current.

Play it safe and use a 4 pin relay, either a new one or a white or grey one from a wrecker. pin 85 goes to the reverse line, pin 86 goes to earth. There is a yellow wire that goes to the trailer plug that is constant 12v, and goes through the door lock fuse (30A) splice into it - relay pin 30, pin 87 goes to the light, earth your light and the job's finished. The relay can be located in the boot, so you only need one wire to go out.

I am assuming you have a trailer plug - if none is fitted, I think the yellow wire still goes into the boot wiring loom.

thanks guys that is a big help