Wiring!! ?

Stupid question. I know. But I know NOTHING about electrical. I can do almost anything else but electrical is NOT my strongpoint so here's my question.

I've wired 3- 100 watt off-road lights to my push bumper on the front of my truck.

I have no problem with the 3rd light as it's all by itself and the wiring is going to its own relay on the inner fender wall BUT the other 2 I'm cornfused on!!

Do I take both wires (from the 2 lights) and splice the wires, tie them together, put on a butt connector and then add a single wire to the other end of the butt connector running that single wire to the Relay to get both lights to turn on when I flip the switch or do I need to run both wires (for the 2 lights) to the relay and then attach them to the relay individually without wrapping them together????? I'm beyond cornfused so a little input would be greatly appreciated. Sorry if this is a retarded question but I'd rather ask and look stupid than melt my truck down to a puddle of plastic. Ha ha. Thanks for any help guys. Cheers!!

 

200 watts
12 volt
vv do math worry less vv
http://www.rapidtables.com/calc/electric/Watt_to_Amp_Calculator.htm

 

Code:

Light     Light

        Y

      Relay

 

100 watts at 12v means 8+ amps per light. You need to know whether the wire you are using is capable of 25+ amps (10 gauge, preferably larger). Also ensure the relay is capable of handling the current.

 

16amps Check your math on my previous post

 

Basically, you can make a Y wire coming from the relay to the lights (of course the legs will be different lengths for light placement). Solder and heat shrink all connections. Where the wire that is on the lights connects to the Y, I would suggest using a weather proof connector or use bullet and receptical connectors with marine grade heat shrink. That way you can remove the lights if needed without having to cut wires.
Also, don't use the cheap relay, get one that is weather resistant.

 

more redundant info, this time with pics

 

I read 3 lights in the original post. It would be 16 amp for the second two, but the feed to the relay would see 25 amps.

 

^^

If all 3 are tied together yes.

 

@Sandman614 has good references. If all 3 lights go to the same relay, make sure the relay and wiring can handle MINIMUM 25 amps, I'd recommend going up a bit to a 30 amps. If you want to overkill, like I do, I would put a 30 amp fuse on the hot wire between the battery and relay. And then 10 amp fuses on each hotwire going to each individual light.

 

*side note I have actually seen this.

 

just remember the formula watts/volts = amps. All automotive (with the exception of rare cases) are 12v DC. So if your lights are 100 watts. Your gonna plug in 100/12 which equals 8.33 amps.

 

+1. Back in my working days, the military derating guidelines for component ratings would have required more like 50 amp rating for the relay contacts for reliability, as I recall.

 

That's why I like that Ampacity chart from the coast gaurd. It has a 10% non-critical rating which covers most things on our trucks, and 3% critical rating which if you're just anal you can use.

 

Ya I could see putting in a 50 amp relay. But just to clear things up your not recommending using a 50 amp fuse, that would be a bad idea.

 

Ya that's a great chart. I downloaded it.

 

I have 2- 25 watt relays. One relay is running one light. The 2nd relay is running the other 2 lights. I have one switch in the cab operating 2 lights and the other switch just operating the one light. Sooooo. I think from what im being told here, I'll splice the 2 wires into one wgoing into a butt connector and from the other end of the butt connector run that single wire back to the relay. Right?? I'm sure it's simple to some but man am I confused. Lol

 

Perfect. Exactly what I needed. Thank you!!!!

 

This is the story right here. Excellent post Sandman. I always design around a 2% voltage drop. Even on something "noncritical" like a light, a 10% drop will be seen in the performance! The 3% numbers will be fine. OP- remember that the wire size you need is dependent on both the current (amps) and the length of run. The longer the length of the wire, the bigger it has to be. This chart allows you to see that. I don't generally solder connections unless they are critical electronic applications. A good quality crimp is fine IMO. I would be sure and use waterproof connectors.