do i need a relay?

Hello,

I just started volunteering with a local fire department and need to wire my vehicle for 2 grill lights and a dash light. These are all LEDs and I'm not exactly sure how to wire this up. I understand the basics of wiring, I have installed amps, speakers and radios in the past. I would like all 3 lights to work off 1 switch on the dash. I am a little unclear if a relay would be required. Can someone please give me some pointers, thank you!

No relay should be required.
Relays usually take more current than relays. (I love it when people switch a 200mA relay to supply power to a 20mA LED... That's assuming "tricky switching" isn't involved, but your LEDs can just be connected between (fused) +12V and GND thru the switch.)

Thank you for the reply.

I thought LEDs amounted to very little draw; but I hate to assume anything. Best to ask when you just don't know.

Totally cool. Better safe than sorry....
If you have any concerns, just ask.

If you are using 12V LEDs (ie, "packages" instead of using individual LEDs and constructing them yourself), it should be fairly safe.

If connected the wrong way (plus to minus etc), they won't be damaged. (Well shouldn't be unless they have some other circuitry which should itself be polarity-protected anyhow. A LED is a diode that glows, and diodes only allow current in one direction.)   


And since they use about half of stuff-all current, they have little impact on loading if added to existing fused circuits.

BTW - there is no point fusing to protect the LED(s), but the wire(s) to the switch should be fused in case the switch or wire shorts to GND etc. And that wiring should handle the fuse current - eg, if on a 10A fuse, then use 10A capable wiring.   (Otherwise insert a smaller fuse unless you are certain no short (overload) can occur - ie, rely on physical protection/security.


PS - a single LED (string) usually takes ~20mA unless special bright ones are used. Hence if a LED "light" is made up of 10 parallel strings (usually with 3 LEDs each if white, ie, 30 LEDs), it's still only 10x20mA = 200mA. That's about the draw of an automotive relay coil or a 2W bulb.

X 2 with Oldspark, just take all the usual precautions with your wiring, cable ties sealed grommets (existing or new grommet + RTV seal) away from hot and/or moving parts etc.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.