Why do I want to use a relay?

[Jared]

Why do I want to use a relay and do I really need to? ... I am still unclear about what a relay does.

Also, I am planning on using a fuse box to power my accessories. If I use a relay on the fuse box, is there any reason to also use one on my lightbar?

[mc88]

Hopefully someone will correct me if I'm wrong, but a relay is pretty much just a beefed up switch. If you run all those amps through some of the little switches (like the horn or lights) it's too much for the switch to handle and can ruin the switch.

And on my last bike I had a fuse box with one relay that I wired to the running lights which only came on when the bike was running. So then if I shut off my bike and forgot to shut off something else, I wouldn't come back to a dead bike. I had a real bad habit of leaving my EMT lights going after I shut off the bike and jumped off to run into the ambulance garage.

And I'm pretty sure if you use a realy for the fuse box, you won't need a separate relay for the lightbar, but better take advice from and expert, which isn't me. haha

[Yellow Jacket]

Suppose that you wanted to wire up your lightbar so that it would come on with the running lights. You could wire the lightbar directly into one of the running light wires. However, since the running lights are on a 10 amp fuse and relatively small wires, as soon as you turned it on with the light bar hooked up the fuse would blow. So, then you could say to your self, "Self, I'll just replace the fuse with a bigger fuse, say a 20 amp fuse." Voila! The light bar works and the fuse doesn't blow! Of course, since you're now drawing a lot more amps through those small wires than they are rated for the wires get hot. Before long the wires get hot enough to melt the insulation. Then they melt the insulation on other wires that they may be touching. The fuse doesn't blow until the mess gets shorted to ground but by then it's too late. You will now be looking for a replacement wiring harness. Not much fun.

Now, if you were to take a 30 amp relay (which is just an electrically activated switch), connect a wire from the battery (or an auxillary fuse panel) sufficient to handle the amp draw of the light bar and connect a wire from the relay to the light bar, again with the proper size wire you could now run the light bar with out melting any insulation or burning any wires.

All you need now is something to turn the relay on and off. For this you can simply connect a wire the same size as that which runs the running lamps to the coil connection on the relay. Connect a ground wire to the other coil connection.

The coil of the relay draws only a tiny amount of current so the running lamp circuit won't be overloaded.

When the running lamps come on, the relay (switch) will close and turn on the light bar.
When the running lamps go off, the relay (switch) will open and turn off the light bar.

All will be well.

P.S. If you connect the light bar to an aux fuse panel, you don't need to wire it to another relay, as long as the total load on the fuse panel doesn't exceed the rating of the relay and the wires feeding the fuse panel.

[ringadingh]

Perfect explanation Bob.

[cactusjack]

Originally Posted by Utah Motorcyclist

Why do I want to use a relay and do I really need to? ... I am still unclear about what a relay does.

Also, I am planning on using a fuse box to power my accessories. If I use a relay on the fuse box, is there any reason to also use one on my lightbar?

A relay is nothing more than a remote-controlled switch. The beauty of using a relay, especially on a motorcycle, is that the juice required to actuate the relay is very small and the relay can switch a much larger electrical load.

I had installed several relays on my Nomad. One for each set of driving lights (2), one to switch each accessory fuse block (2), and one for power to the fairing.

My thoughts are, if you are wanting to power anything that draws more amps than a GPS, then use a relay.

[BudMan]

Well, that about sums it up.

[Jared]

Originally Posted by cactusjack

A relay is nothing more than a remote-controlled switch. The beauty of using a relay, especially on a motorcycle, is that the juice required to actuate the relay is very small and the relay can switch a much larger electrical load.

I had installed several relays on my Nomad. One for each set of driving lights (2), one to switch each accessory fuse block (2), and one for power to the fairing.

My thoughts are, if you are wanting to power anything that draws more amps than a GPS, then use a relay.

Did you run your lights to your fuse block? Any reason you used a relay on the lights and then again on the block?

[cactusjack]

Originally Posted by Utah Motorcyclist

Did you run your lights to your fuse block? Any reason you used a relay on the lights and then again on the block?

The fuse block was the power supply to power the lights. The fuse block was switched with a relay so it only had power when the key was on. The relays for the lights were to turn them on/off from a handlebar mounted dual accessory switch and later from rocker switches in my fairing.

[Jared]

Okay, let me get this straight, if I wire a relay exactly like show on gadgets (written by Scott, right?) I should be good to power all my electronics to it? I was planning on using a 30a automotive relay. This is the right equipment right?

http://www.gadgetjq.com/auxiliary_fuse_box.htm

[Jared]

Also, my fuel processor says to tap into the rear brake light power because it is only on when the key is on.

If I use a relay on my fuse box, am I good to power it from the fuse box?

[cactusjack]

Originally Posted by Utah Motorcyclist

Okay, let me get this straight, if I wire a relay exactly like show on gadgets (written by Scott, right?) I should be good to power all my electronics to it? I was planning on using a 30a automotive relay. This is the right equipment right?

http://www.gadgetjq.com/auxiliary_fuse_box.htm

Oh boy, that was an early drawing. Yes, it will work. 30a or 40a relay, whatever you can get hold of.

[cactusjack]

Originally Posted by Utah Motorcyclist

Also, my fuel processor says to tap into the rear brake light power because it is only on when the key is on.

If I use a relay on my fuse box, am I good to power it from the fuse box?

Yes, it just needs to be a switched power source.

[ringadingh]

Your correct on both counts, as long as you use a switched wire for the trigger on the relay.

[BudMan]

Tapping into the brake light will only give you power when you hit the brakes. I suspect it means taillights.
The taillight circuit will be "hot" whenever the key is on.
If you are using an aux fuse box then just use a relay to turn it on
and there will be no need for relays downstream of the fuse box.
But you will need a 30 amp inline fuse between the battery and the relay.
You can then run whatever accessories you want from the fuse box and they will only be powered on when the key is on.
But keep in mind you are limited to the 30 amps (fuse & relay).
Just use the correct size fuses in the fuse box and the appropriate size wire for each circuit you run from it.

[Jared]

Perfect. I think I kinda get it....?

Is there accessory that you wouldn't want to use a switched wire for? Seems like you wouldn't want anything draining the battery while the bike is off.