electrics and relays

wiring diagrammes, how to's etc
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Joined: Sun Feb 24, 2008 8:37 am
Location: Upper Ferntree Gully

electrics and relays

Post by flexyourhead » Sat May 19, 2012 7:59 pm

Hi again,

I'm now in the middle of wiring my bike back to ignition switch etc. As I was working on the key switch/barrell component, it literally fell apart in my hands. Spring popping out one direction, something else popping out the other etc etc.

I spoke to a locksmith friend as he can get new key switches but when I explained I was after a keyswitch which goes from 'OFF' to 'ON' and then a final stage being 'ON with LIGHTS', he seemed to think I'd be crazy to run coils etc, light and horn all through the switch and should really be run through relays off tthe keyswitch.

I have no problem with this concept but in all the wiring diagrams I've seen around and including ones from this site, none have referance to lights, horns, coils etc being run through relays. They've all been shown to rum from the battery, through the ignition switch and then off to whatever they're powering.

Is my locksmith friend being overly cautious with the fear of melting the ignition switch with lights and the like running through it or is there no issue with running straight through the ignition swich as the overall current draw is so small, the ignition switch should handle it with ease.

I'm only running a front light Hi & Lo, horn, rear tail light, rear brake light and igniton (coils)

Any input is appreciated.


Founder, Choppers Australia
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Re: electrics and relays

Post by Prof » Sun May 20, 2012 10:28 am

Ignition switches have been used from time immemorial for running ights, ignition and accessories. The only time you need a relay is when a component has very heavy power draw such as starter motor (use a magnetic solenoid) or running a 100w driving light off your high beam switchor an air horn (relay).

HD after market ignition key switches have the positions you want and are cheap.

I personally use toggle switches for ignition and lights... they are simple, small, cheap and I can easily carry a spare in my tool kit though I've never needed to replace one on the road yet.

If you want to run a 100w high beam, it would be worth using a relay, or if you want to connect a second driving light up to high beam you would definitely need to.

Relay wiring is really simple. Think of a relay as a remote switch. It has power in and power out, but instead of your finger activating it mechanically an electric current does it... so

Your relay will have 4 or five pins,

Two or three of the pins are the actual switch circuit...
On the five pin relay you have two outlets(#87) to go to the components (eg two driving lights)

#30 is power directly from your battery
#87 is the switched power that goes to your component(s)

Remaining two pins are for operating the relay...

#86 supplies power from your finger operated switch eg high beam side or your high/switch
#85 goes to earth (remember that 12V DC needs to do a full circle)

Here's a diagram off the net... easier than drawing one myself...

Chopit'nrideit... Prof

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