Emgo Key switch + relay

I have the Emgo Key switch going into my CB550. I search online and apparently these tend to fail without a relay.

Can someone pls assist in wiring the key switch > relay > munit?

Emgo Key switch wires:
- red: power?
- black: ignition?
- brown:
- brown/white:

Relay wiring:
- Key switch red wire —> fuse —> battery.
- Key switch black wire —> #86 on relay.
- #85 relay —> ground (frame).
- Battery —> fuse —> #30 on relay.
- # 87 relay —> munit ‘lock’ input.

Is the above correct?

Thanks,

If you're using an m-unit, you won't need the relay (the m-unit acts as its own relay for this application).

From the m-unit to the switch: Positive terminal of the m-unit -> 1A fuse -> Red wire on switch
Then back from the switch to the m-unit: Black wire on switch -> Lock port on m-unit

Skip the brown and brown/white wires. Cap them off to avoid short circuits.

Thanks! I had it originally wired as you said but reading up I was worried the key switch may fail

CB550F said:

Thanks! I had it originally wired as you said but reading up I was worried the key switch may fail

Click to expand...

On their own, yeah. With an m-unit, you're OK though.

The problem with the Emgos is that their wires are a bit too thin for switching main power. When you use a relay or an m-unit, you're switching a much lighter load and the thinner wires are just fine.

What wire size will I require to run from munit battery termail > 1A fuse > red key switch? The bigger the better or do I go depending on the 1A fuse?

Anything 20 gauge or thicker will work.

I would use 18 because it's not quite as fragile as the 20, though.

Say I add a 15amp wire for power to the switch, will I require a 15amp fuse or I can still use the 1amp for key power to munit?

Fuses should be sized as small as possible, based on the amount of current you're expecting in a circuit and the amount of current that can be handled by the wire and components.

In this instance, the m-unit only uses a very small amount of current for the "lock" feature, so a 1A fuse is all you should need for this application.

The fuse size is determined by the amount of current pulled by the components and the wire is then sized according as well.

For instance, if you have a 55W headlight, the headlight will be pulling 4.5A at 12V. When your bike is running, you're usually around 14.5V, so the headlight will really be pulling 5.5A (we can go through the math on this, if you'd like). Next standard size up on the fuse would be 7A. Then we look at wire ratings and see that in order to run 7A through stranded copper, we want at least 18 AWG. Thicker wire is OK, but thinner wire is not. Choosing a smaller fuse might be OK, but you do risk the chance of blowing it. Using a larger fuse would NOT be OK because a short circuit might start a fire.

Thanks for the advise Sonreir! Much appreciated! I’ll stick with the smaller fuse