Thickness of Ground Wire?

I am installing a traffic backer (it alternates the brake lights and the back up lights) on my car. Instructions recommend I use a 16 gauge for the positive (white) wire and it be connected to a switch. Two questions: 1. Would it be OK if I just have it ALWAYS connected to power and instead connect the ground to a switch? 2. Can I use a thinner wire for the ground or does it also have to be 16 gauge? Thank you

1. No, not a good idea. 2. The ground can be a smaller gauge as it only has to handle the current required by the controller itself - not all the loads. 20 or 22ga would be fine.

The switch is required to prevent a constant draw on the power source which would drain the battery. The ground wire should be the same gauge of the input power wire. The schematic does not indicate the fuse rating on the circuit. The ground wire must be the correct gauge for the current load of the circuit. Generally speaking unless the ground wire is for relays which don't consume current, then always match the gauge of the ground wire to the power wire. If the wire must be extended, then use a lower gauge (thicker) wire to reduce voltage drop.sparky

sparkie wrote: The switch is required to prevent a constant draw on the power source which would drain the battery. The ground wire should be the same gauge of the input power wire. The schematic does not indicate the fuse rating on the circuit. The ground wire must be the correct gauge for the current load of the circuit. Generally speaking unless the ground wire is for relays which don't consume current, then always match the gauge of the ground wire to the power wire. If the wire must be extended, then use a lower gauge (thicker) wire to reduce voltage drop.

Making the ground conductor the same size as the feed conductor is necessary if all the current supplied to the loads must pass through one ground conductor. That is not the case here as the loads all have their own grounding conductors. The only current flowing through the dedicated ground wire from the controller is the current consumed by the controller's electronics.

Thank you everyone, I'll keep the positive wire switched and use the same gauge wire for the negative as for the positive.