Help with wiring diagram - Backup Lights

[the_new_nomad]

Can anyone share a diagram and relay type that would allow me to run aftermarket back up lights that turn on when in reverse, but also allow me to manually turn them on via a rocker switch in the cab no matter which position the transmission is in.

 

[4x4junkie]

This help? (substitute 12VDC from your backup lamp circuit for the headlamp circuit)

 

[Hilldweller]

Switch them with the reverse function also. It's not legal to have a set of auxiliary lights on your reverse circuit that don't have a defeat switch.
The diagram above does that but I'd use two switches and two relays just in case I ever wanted to change things up.

 

[the_new_nomad]

Thank you for the quick responses. So with the diagram above, if I were to have a switch with an LED light, and was always in reverse light mode (opposed to always on, or off), it would be a constant drain on my battery correct? So if I were to do it this way I should get a non illuminated switch?

 

[DiploStrat]

3.5 Comments and a Resource

1. Good multipurpose diagram - can be used for all kinds of lights (driving, fog, etc.) that you want to be controlled directly from your vehicle's factory wiring. That is, your auxiliary lights will respond to things like your high beam switch, reverse gear shift position, even your horn. (Yes, I use this kind of wiring to trigger air horns.)

1.5. Bonus points for the diode, required by Chevrolet (and others I would expect) to protect computerized circuits.

2. Note however that many modern vehicles do this switching on the negative, not the positive side. For example, your headlights may always be connected to 12v. They come on only when you complete the negative side of the circuit. (This allows the vehicle computer to monitor the state of your bulbs, etc.) Switching the negative is not any harder but you do have to think about it for a moment and use relays that are not grounded through their cases or mounting brackets.)

3. You can get very clever with switching and telltales. For circuits like this, I like telltales that respond not to the position of the switch ("dependent") but rather to the action of the circuit ("independent"). In this case, I would want the telltale to come on only when the rear lights are actually lit. With a bit of care, you can arrange "always on", "always off", and "automatic" settings. Similarly, you can use LED and incandescent telltale bulbs.

Lots of resources for both switches and circuits here: http://www.otrattw.net

 

[4x4junkie]

Thank you for the quick responses. So with the diagram above, if I were to have a switch with an LED light, and was always in reverse light mode (opposed to always on, or off), it would be a constant drain on my battery correct? So if I were to do it this way I should get a non illuminated switch?

If it's wired up as shown, the LED shouldn't light when your reverse light circuit is not energized (so no constant drain on your battery if the switch is left in the on w/reverse position).

2. Note however that many modern vehicles do this switching on the negative, not the positive side. For example, your headlights may always be connected to 12v. They come on only when you complete the negative side of the circuit. (This allows the vehicle computer to monitor the state of your bulbs, etc.) Switching the negative is not any harder but you do have to think about it for a moment and use relays that are not grounded through their cases or mounting brackets.)

Interesting to know. If this is the case, accommodating it should be just a matter of tying your relay (pin #86 in the diagram) directly to +12V, and then wiring your switch onto the negative or 'ground' side of the relay (#85). The indicator LED (if used) would then be moved to +12V (pin #86) and #85.

Yeah I always put diodes on my relays. Even if nothing else, it helps save some erosion of the switch contacts.