Wiring factory reverse lights to auxilary switch

[mattging94]

I recently upgraded several bulbs on my ranger to LED, including the reverse lights. They seem like they are bright enough to use as an auxiliary work light so I would like to wire a separate switch to turn the reverse lights independent of reverse gear, but I'm finding very little information out there about how to do it.
I found one wiring diagram that seems like it would do what I'm trying to achieve:

I understand using the diode to prevent backflow into other parts of the electrical system, but to me it seems unnecessary to use a relay for just the factory reverse lights. The factory circuit runs directly from the reverse switch to the lights as far as I know, so why should adding a 2nd switch change that?

Here is a circuit that I came up with that I think would work without using a relay:

Can anybody confirm that this circuit will work for what I'm trying to do?

 

[RonD]

yes you could do that with the diodes.


I think you are over complicating things with the relay though.

You want a 5 post relay, 12v 30 amp, they are cheap and the relay socket.

Relay has pins 85 and 86 for the coil, when one is ground and the other 12volt, relay will close, if you cut the Ground OR the 12v then relay opens.

Now the Load pins, 5 post/pin relay will have 30, 87 and 87A
When relay is off/open pins 30 and 87A are connected, 87 is disconnected
When relay is on/closed pin 30 and 87 are connected, 87A is disconnected

So you cut the wire coming from reverse switch to the reverse lights

Hook the wire from the switch to 87A
Hook the wire to the lights to 30
If relay is off then reverse lights are back to normal, just a straight connection as before.

Hook up your 12volt fused power to 87.
When relay is on/closed trans switch is disconnected, no diode needed, and 87 is connected to 30 so reverse lights are on.

You could also hook up that same 12volt fused power to pin 86 with a jumper.
Then run pin 85 Ground wire up into the cab, your switch in the dash would Ground pin 85 turning on/closing the relay.

Most relays in cars/trucks are controlled by Grounding, running ground wires means less chance of shorts that could blow fuses or melt wires.

pin 86 12v fused power
pin 85 Ground

pin 30 Reverse light bulbs
pin 87A reverse switch on trans
pin 87 12v fused power

Current reverse light wiring:
Power from key on-----------trans switch----------------------reverse light bulb------ground

Change
Power from key on-----------trans switch---------87A(relay)30-------------reverse light bulb------ground


Images of 4 and 5 pin relays here: http://www.reuk.co.uk/Automotive-Relays.htm

 

[mattging94]

Thanks RonD, that makes sense. I think the diagram I found with the 4 pin relay and the diode was meant more for adding additional rear lights and not adding a second switch to the existing ones.
After doing a little more research on diodes it seems that you lose a little bit of voltage across them, which would cause the lights to be slightly dimmer. The 5 pin relay set up would not have that issue, so I think that is the best option

 

[RonD]

Yes, I would agree, relay would be better choice long term

 

[4x4junkie]

You just want to turn on the existing factory reverse light circuit (while not in reverse)?

If so, all you should need is to put a 2nd switch in parallel across the factory reverse light switch on the trans (or trans shifter). When either or both switches are closed, the lights will come on. No diodes or relays should be necessary for this.

 

[adsm08]

Yeah, I am with 4x4. Both you and Ron are making this far to complicated. Get a 30 amp switch, and wire it up like you did in your paint diagram, but with no relay. The fatory switch your keep any voltage from going back any farther if it is open, no that it should be a huge concern anyway.

 

[mattging94]

Ya know when I first came up with the idea to do this mod that was how I thought to do it - just a simple switch in parallel with the factory reverse switch. But then when I started trying to research things about it online I kept finding things saying you don't want current to backflow into your reverse switch... Of course when I was looking for information on how to do this everything I was getting was for wiring additional rear lights, not rewiring the factory ones. I'm kind of surprised there was nothing out there for this mod - seems like a good way to add a little bit of working light to the rear of a rig without actually adding lights

I already went out and bought a 5 pin relay, and since it wasn't expensive I think I'll just use it anyways, incase there is anything to that whole back-feeding thing

 

[RonD]

If you use the 12volt Reverse light wire then key needs to be left on while using the lights.

And you really wouldn't need anything more at that point, no extra switch, just set e-brake and put trans in Reverse, assuming automatic.
If manual then just leave it in Reverse and turn on the key

I assumed the OP wanted the reverse lights on without key on

 

[mattging94]

Yes the new switch would run the lights on key-off power direct from the battery