PC-8 Kit - what does the relay do?

[philipmat]

I'm bringing shame upon my village and my Electrical Engineering degree (to be fair it was a minor).

I see the PC-8 comes in fuse-panel-only flavor, but also a complete kit with a relay. I'm assuming I'll be needing the latter, but for my own edification: what purpose does the relay serve in this setup?

 

[SkunkWorks]

I believe it is so you can power the fuse-panel directly off the battery, and use an ignition-on-only circuit lead to trigger it.
That way if you want the whole fuse-panel on with ignition, you are not loading all the current through one circuit.
That's how i would wire it on mine.
I have a small fuse-panel wired this way on my FJ1200.

 

[RCinNC]

The relay is just an electronic switch that allows the PC-8 to be turned on and off at the same time the bike is turned on and off. That way, anything connected to the PC-8 won't draw any power when the bike is shut off, even if the device itself is still on. If I recall correctly, the PC-8 does have the option of two "always hot" circuits that connect directly to the battery.

A relay also allows you to divert the current of a circuit so the load doesn't pass through the sometimes delicate components of a switch. You'll see this in something like a headlight relay. A low current can pass through a switch, which goes to the relay, which activates a heavier duty switch in the relay, which can handle the higher load of the headlight circuit so the load doesn't go through the switch itself.

 

[AVGeek]

The PC-8 has an option for both switched and constant hot circuits, so the relay is for the switched side.