Relays?

Shawn84 · February 6, 2008

I have a list of things to install in my truck this year and am trying to think of the easiest way. Can i tap into my cigerette lighters and add a relay and a fuse for my CB or should i run a hot line directly from the battery. I'm going to be installing my Fire Scanner and a CB and i have 2 cigerette ports next to the slots. Just cuurious on how relays work and was the rules to them are. Will they cut the power to any hot line when the motors off or what?

Zembonez · February 6, 2008

A relay is basically a coil activated on/off power controller. The coil side is a low amperage circuit that switches the main high amp circuit when you activate it. When the coil power is switched off, it disconnects the high amperage circuit. This way the switched circuit doesn't have to carry the current of the power side.

Shawn84 · February 6, 2008

but can i just splice into the cigerette lighter, add a relay, and wala instant power that is only on with the truck?

Zembonez · February 6, 2008

but can i just splice into the cigerette lighter, add a relay, and wala instant power that is only on with the truck?

The main power for the relay would come from the battery. You could run a switch leg off of the power side and switch it by switching your ground but I would look for a switched power source for the coil. Most relays come with a diagram. I would leave the lighter circuit alone.

Here is an example.

Shawn84 · February 6, 2008

so what do you think the smartest way to wire my CB and Scanner would be then? I don't want to involve a switch. I want them on when the ignition is on.

-db · February 6, 2008

Wire it like this.

12 volts from a constant power source to pin 87

Power from an Ignition wire to pin 86

Constant ground to pin 85

New accessories to pin 30

You can get both power and ground at your ignition harness at the steering colomn.

Shawn84 · February 6, 2008

ok what size relay would you recommend and can i run both my CB and scanner off of one relay? I know i must be annoying with the questions.

-db · February 6, 2008

A normal relay is rated for 30 amps which is well more than enough for what you want to do.

Shawn84 · February 6, 2008

alright thanks for all the help everyone.

Shawn84 · February 6, 2008

So would this work in theory? and if it does what gauge wiring and relay would recommend.

MustGoFaster · February 7, 2008

looks good for the most part. although I would add a 30A fuse inline between the relay and battery - just in case something totally bizzare happens. The only question I have is the air compressor - are you planing an air ride kit or bags? if so, those are pretty high demand units and might require their own relay and power source. The lights should be ok on the same circuit provided you're not trying to run more than a pair of driving lights or smilar.

Watts = amps X volts, so figure a 30A relay x 12 volt system = 360 watts. if you use 2 100 watt bulbs for lights, (which will draw 17-18 amps tops) then you have just enough room for a CB and a scanner.

for a switched ignition source - you could tap one of the leads from the truck's fuse panel - several of those lines are run by an ignition relay as well - or else you could locate a wiring diagram and find a switched source underhood to make life simple.

Shawn84 · February 7, 2008

After i made that diagram i thought about a fuse or breaker between the battery and relay. As for the air compressor it will be for air horns but you're probably right i should wire it seperate.

Zembonez · February 7, 2008

After i made that diagram i thought about a fuse or breaker between the battery and relay. As for the air compressor it will be for air horns but you're probably right i should wire it seperate.

I agree that you should run the air compressor on another circuit but you are certainly on the right track. Tripping the relay with an ignition on hot circuit does mean the you can't use any of these items without the key on though...