12V LED Light Bar Dual Input Wiring

Thread Starter

CalhounMoto

Joined Feb 27, 2024
1
Not sure if this is the correct area to post this in, but I need some help. Yes, this is kind of dumb & pointless, but I think it would be cool to have this functionality.

I am looking to install a 12 volt LED light bar on my truck. I would like to use a 3 way switch to control the lightbar as follows:

Switch Position 1: Light bar comes on when headlight high beams are activated, and turns off when high beams are deactivated.
Middle Position: Off - No power to light bar.
Switch Position 2: Light bar constant on regardless of headlights being on.

I plan on using the power from the switch, and the high beam circuit to control a relay for the light bar. It would be very easy if I could find a switch with 2 inputs, and 2 outputs, but I have not been able to find one.

Just not sure how to get this wired correctly to make it work (if it can work).

I appreciate any assistance!
 
Last edited:

MisterBill2

Joined Jan 23, 2018
18,442
This is not a hard project, except for pulling the wires. Depending on how much current the light bar draws, you might need a relay to switch the 12 volt power. So I will start with a guess that the light bar draws 20 amps and so you must use a relay to control the 12 volt feed. You also need a single-pole three position switch so that you have a center off position. From the battery positive, a 30 amp fuse, and then the wire from the other side of the fuse goes to terminal #30 on that 30 amp automotive cube relay. Then the wire from terminal 87, the normally open contact, goes to your light bar positive input connection. Back at the relay, a wire goes from terminal 85 (coil connection) to the body ground (thin wire, only carries relay coil current. A wire from terminal 86 (other coil connection, goes to the common terminal of the switch. (terminal "C"). Next another thin wire goes from that switch position #1 to the HI BEAM headlight feed. That lights the bar when you hit HI beams on. Then a wire from switch position #3 connectes to the accessory feed, so in the ON position the light bar only can switch on when the engine is on, or at least a responsible person switched on the key. That is all there is to it!!
 

MisterBill2

Joined Jan 23, 2018
18,442
How about using a single multi-pole high current center-off switch without a relay?
The reason I did not suggest that is that adding that much current to the high beam headlight feed current might cause an overload failure. In addition it would require three heavy wires to the heavy duty switch. But that was my first thought. The other reason is that with a single relay the relay might fit up in the light bar and there would only be one heavy wire and one fuse required.
 

eetech00

Joined Jun 8, 2013
3,928
The reason I did not suggest that is that adding that much current to the high beam headlight feed current might cause an overload failure. In addition it would require three heavy wires to the heavy duty switch. But that was my first thought. The other reason is that with a single relay the relay might fit up in the light bar and there would only be one heavy wire and one fuse required.
That why I suggested a multi-pole switch. That's all I could suggest without knowing the wiring.
One set of contacts could be used to switch the low current headlamp relay, while the other contacts could switch power to the light bars.
 

MisterBill2

Joined Jan 23, 2018
18,442
That why I suggested a multi-pole switch. That's all I could suggest without knowing the wiring.
One set of contacts could be used to switch the low current headlamp relay, while the other contacts could switch power to the light bars.
The way I did the circuit, only one relay needed and no heavy current at the switch. Quite a bit less heavy wire needed. AND a low-power switch. Identical functions: Position #1, light bar with hi-beams, position 2, OFF, position #3, ON when the accessory switch is on. OR position #3 could be just ON, for any condition.
 
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