Some help for dual switch and a dimmer on side/camp lights?

Wilbah

Adventurer
So I've looked a lot of places here and on the web (on the web I keep getting directed to household 3-way switches). I have seen some dimmer switch diagrams but its usually a single light "system". I have contacted some off road lighting companies hoping they had a diagram for this but did not get any ideas back from them.

What I would like to be able to do is have a flood light mounted on the side of the vehicle. I want to be able to switch it on from the cab/drivers seat to light up the side at full intensity. I also want a switch at the rear of the vehicle that allows the same. But I also want to be able to dim it from the rear for those times in camp where I don't want full intensity and instead want some "lesser" light. I am not positive this would work so put it to you guys who know a *bleep*load more than I do on this stuff!

So I put together these three "scenarios" that I could use some help on. I want to run all this on a bench initially to see what works and what doesn't but the last thing I want to do is "try it", have it (sort of) work and then burn up my vehicle because I missed something obvious. Which is why I'm here posing it to you all! :)

#1- I get using relays (thanks to you guys) to lessen power draw need at the switch.

#2 But it's not clear if I can link two switches to one relay? It "seems" to me that the relay would "trigger" with any current so either switch would work to power the light? But maybe I need two relays? One off each switch? I am also somewhat uncertain about distance- would it be okay to have the relay at the rear of the vehicle and run the lower current line from the switch in the cab? Or do switches need to be nearer the relay in which case maybe I should use two relays- one up front and one in the rear? But this doesn't really get me to where I want to take this so I went to #3 below....

#3 I figured if I wanted a dimmer I couldn't just put that after the (a single) relay because then the dimmer at the rear of the vehicle would control the light all the time (which I could solve by remembering to always turn it back to full when I leave camp, but I don't trust myself enough that I would always do that). So, I figure to have the dimmer I would need two relays. One which runs the switch from the cab which always provides full light. The second one at the back of the vehicle then has the dimmer attached. But I don't know about power feeding back and forth there or if power feeding back to Relay #2 from Relay #1 (when I turn the switch on in the cab) would cause a problem?

Anyway I figurSwitch Diagram.jpge others may have solved this already so I am wondering what you guys would do? Thanks!
 

llamalander

Well-known member
As said above, relays can make things more complex than you need. If you know the draw of the lights and the length of wire to power them, you can size the wire to minimize voltage drop and skip the relay. LED lights can be very bright with just a few watts, so even a large array will not draw so many amps that you can't use common wire sizes.
For the cab, run a fused power line to a 3-way switch (either/or, single pole double throw) and run 2 power lines and a ground back to the rear. There you use a second switch (3-way, spdt) that goes to your 12v. dimmer, then on to the lights. If you want to be able to forget the dimmer, run 2 SPST switches from the same fused power source, one in the cab & the dimmer in the back, to the lights and hope that the dimmer is ok with back-fed power.
12 gauge wire should make that circuit for 150 watts of lighting with a comfortable margin, you may not need wire nearly that thick. Measure the total length of the circuit, from the battery and all the way back (don't count on grounding to the frame, just make a home run and skip the trouble of intermittent connections), and look up what gauge wire you need for your voltage drop (try <3%) and see what wire gauge you need for 125% of your total lamp wattage. 12-14 gauge wire takes as long to pull as 20 gauge, except that you don't have to do it more than once.
http://assets.bluesea.com/files/resources/newsletter/images/DC_wire_selection_chartlg.jpg
 

Wilbah

Adventurer
Llamalander thanks... I "know" about keeping the wire size larger to minimize voltage drop but have not been sure of the amounts, distance etc to be able to ensure i am using the math correctly. The link is very helpful. I appreciate it!
 

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