I installed dual 30" light bars in the grill of my F150. They are awesome. The only downside is each came with a seperate harness(with relays, fuses, and switch).

I hate having 2 switches to turn them both on. I want them both to turn on with a single switch. The company I bought them from doesnt make a single harness for both lights.

The switches each have 3 wires running to them. Any reason I cant just splice the 3 wires from each switch together and run them off a single switch? Each lightbar would still get power from its own wire harness/relay/fuse. The single switch would just send the signal to each light bars relay...... atleast thats how I think it would work.

Or am I way wrong and going to blow the truck up?

That'd be even easier!!

Thanks

What he said. One wire is a ground to allow the indicator LED to illuminate

Double tap

Depending on the wire used and the max amp draw of the lights you don't even need 2 relays and 2 source wires.

I mean, you could do one heavy gauge wire from the battery to the power input on the relay or solenoid(provided its big enough to handle the load), then come off that with the correct power wire to each light bar.

I have used a relay to trigger up to 8 amps in a car stereo (only 8 because that's all I had) granted the remote turn on draws very little power. I have also wired up the air bag system on a several trucks to have 2 and 3 compressors running of the same solenoid.  
Just one fat power cable from batt to it, then from it to the compressors.  

I tried doing this with a bank of lights I put on my quad and every time, I blow the fuse.
if I don't use a switch?? just direct wire, everythings fine


what am I doing wrong??
I DID apprentice for 1 year as an elecricitan and think I know what I"m doing,
wired my own house and done general repairs in others...so have some general knowledge, enough to be dangerous.

Are you using a relay?

Using a switch to a relay should be a non issue.  If you are not using a relay you are passing all that amperage through a switch contact and creating resistance.

12V Relay signal wire is very low amperage. You can easily trigger multiple relays with a single switch by just connecting them together.

One switch wired in parallel to the coil sides of two relays, one relay per bar.

The control ( coil) power can come from a different circuit than the power for the light bars.

You trying to light up the moon or something,  leave them separate,  having both on is overkill.

You can even run the ground through the switches so there are no random power wires under the dash and everything "hot" can be isolated near the battery - relays - consumer. Assuming you don't need the fancy switch illumination. But then you could run 12v from an interior switched light to your switch and they'll only illuminate with the lights on, unless they're LEDs and care about polarity.

The relay "trigger" draws very little power. One switch will handle multiple relays no problem.

12v wiring is stupid simple.