Running 4-50w aux lights off of one relay

[WagoneerSX4]

Is it possible to run 4 - 50w hella 500FF driving lamps off of a single 40A relay? I'm finally getting around to redoing my harness and I'd like to simplify it by wiring all 4 together instead of 2 switches. I know I need 12 gauge wiring since (50x4)/12v=16.7A and 12 gauge of less than 50ft can handle 20A. I figure a 40A relay with a 30A fuse (or should I go 15A fuse since that's roughly 80% of the amps needed?), all 12 gauge wire except 14gauge going to the switch.

Does that make sense?

 

[vicali]

You could wire both relays from one switch- but having duplicate harnesses in there with smaller loads on lower gauge and smaller relays would be better/cooler/safer than running one harness with a big relay and heavy wiring.. What if you have a short?- or you decide to upgrade bulbs?

I run two separate harnesses with 10g+30A fuses, that way I can always upgrade to 100w bulbs in the future..
I like having two switches for my 4 500FFs, the centers are aimed down the road and the outsides are in the ditches.

 

[WagoneerSX4]

You could wire both relays from one switch- but having duplicate harnesses in there with smaller loads on lower gauge and smaller relays would be better/cooler/safer than running one harness with a big relay and heavy wiring.. What if you have a short?- or you decide to upgrade bulbs?

I run two separate harnesses with 10g+30A fuses, that way I can always upgrade to 100w bulbs in the future..
I like having two switches for my 4 500FFs, the centers are aimed down the road and the outsides are in the ditches.

That was my main thought when making two harnesses at first (same as you - two aimed forward and two to the sides) but i've never used them separately. I was also thinking it would be easier to find an issue out in the middle of nowhere with less wiring/relays.

I don't think i have plans to upgrade to 100w. The 50w bulbs are more than adequate, especially with my 55w HID projectors in my headlights. I really only use the aux lights to get hot spots where I need them.

 

[vicali]

I was also thinking it would be easier to find an issue out in the middle of nowhere with less wiring/relays.

Or spare parts? lol, it's 50/50 really.

I run them this way for another reason as well, see here in BC you are allowed 2 additional driving lamps.. so having them separate means I can use one set on the highway legally.

 

[WagoneerSX4]

Haha, I'm not worried about that in Ontario. Our HTA says you're only allowed 4 forward facing white lights (even if they're not on). So basically any vehicle equipped with fog lights is already capped out for lights. Technically I need to drive around with opaque covers on my hellas for it to be legal. But every cop here knows it's a ridiculous law to hand out tickets for and it's only in place for idiots running around with 8 lights on their cars blinding on-coming traffic in cities. Not something they're looking out for.

But I leave the covers on anyways. I take them off before a trip where I know I'll be using them.

 

[Pccruiser]

Yes one relay is fine. Wire your lights in series down into the one relay controlled by one switch.

I = P/V

Amps = watts / volts

So at 50x4 watts your relay needs to be able to handle 16.67 so a single 40 is fine.

Exactly how I wired my 4 55 watt lights.

Don't forget to check your fuse though. Mine came with a 15 amp inline fuse that I needed to upgrade to 30 watt. Slow reaction fuse.

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[WagoneerSX4]

What gauge wire are you using?

 

[vicali]

Wire your lights in series down into the one relay controlled by one switch.

So at 50x4 watts your relay needs to be able to handle 16.67 so a single 40 is fine.

Lights in parallel, relay trigger and switch in series.

What gauge wire are you using?

20A-240W 10ft is 12g;

 

[Pccruiser]

Lights in parallel, relay trigger and switch in series.



20A-240W 10ft is 12g;

Yup parallel and the switch is series. Silly me.

And I used 14 ga. But I only had about 5 feet worth. Maybe less.

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[evldave]

Those wire ratings are the minimum wire size. For lights, which seem to be very susceptible to voltage variation, I always bump up one (sometimes 2) wire sizes. This helps prevent light flicker. I figure the cost is basically the same, so a little insurance on the wire size works well.

As a note, I run 12GA on my 500FFs.