How to wire an automotive spdt relay to power more accessories

30 is your power in, 87 is your power out to device. Hence the 87a (also power output to a device), which is on when the switch is off where 87 is on when the switch is on. The way you have it setup technically works, but power flows the wrong way, essentially connecting 87a and 30 (your device) together when the switch is off and disconnecting 87a from power when the switch is on.

You’re a great teacher bro…that explanation was really clear made complete sense! Thanks for posting!!! 👍🍻

thanks JP for explaining, my 05 chevy express orginal radio harness didn't have the switched 12VDC the fuse blocks are very hard to acess. so I'll connect my first relay to climate controls stealing it's switched 12VDC an steal the constant 12vdc & ground from old radio harness. out 30 to new radios yellow wire switched 12vdc. excellent video

Great job, man. I've watched a few relay videos and yours by far has the clearest explanation of how they work. Thank you

Lots of useful information that relates to my situation regarding LED. Very clearly and simply explained. Much appreciated for taking the time to post this.

Thanks, this will help for the relay for a vacuum pump...and the switch

You've made this make sense. Thank you 😊

Good video man. Thanks for the info!

Another helpful and informative video by you. Thank you for your selflessness and the help you provide to the normies like myself. I have used relays in the past but your video helped me actually understand in layman's terms how and why they are required/applied.

Dude, you're awesome. know your stuff. good work

good explanation

excellent video very detailed and helped me a lot, my question is why do you have a jumper from 86 to 87 ? just curious wouldn't that have a constant source of power... on 86 and 87 ?

Dope!!

Good stuff…nice video

You did that all wrong 30 goes to the battery 86 is your low voltage power 85 is ground 87 comes on when low voltage is on and 87a has power when there is no low voltage present and opens when low voltage come on

Have you seen the video bare vids did where he hooked up 8 amps of all different types and it still pulled less current than a relay by itself?

I have some footwell led lights and a map light I want to wire together to the same ignition source. I used an empty spot on the fuse box. Since the spare map light is white and I’d use it for maybe a minute to find something, but I’d use the LED’s by themselves for longer periods, Would this be okay? I wouldn’t be drawing power from them constantly- most of the time they won’t be turned on. And probably never at the same time.

I have drl strips and can i tap into a relay inside fuse box to make them turn on when cars running and off when its not?

Hey, I've got a LED switch that has 4 prongs on the back. What's the best way to wire that up using a relay? I was thinking the top two prongs are hot/ground for the switch itself...and once the switch is flipped it sends power out using the bottom two prongs. Would I need to use both bottom prongs to hook up to the relay? Think I would only need the 'hot' side to go into the relay? 2nd question, what's a good place to ground that LED switch inside the car (driver's side)? Trying to avoid running a ton of wires through the firewall. Hoping to tap into the in-car fuse box (down by driver's left knee) for the switch and then ground it somewhere in that same area. Then run the hot wire from the bottom prong out through the firewall to the relay that'll be in the engine bay. I'm wiring a lightbar to the top of my car. I'm using a 20amp relay (lightbar is 16amp) Thanks!

Thanks, I was trying to see if I could run a second relay off of the first or if I needed to tap into a second remote wire.