Faulty kill switch?

750 1971 Roadster. Fuses started blowing recently. I have a TriSpark Tri0005 ignition unit. I have narrowed it down to the kill switch (I think). I have the black/yellow wire from the ignition module connected to white/yellow wire from the Left Hand switch for my kill switch circuit. When I ground this connection to the frame I get continuity and my multimeter beeps. Closed circuit? When I press the kill switch in this situation the beeping stops. Open circuit? Is this normal? Should I bypass the kill switch? Buy a new switch cluster? Any advice is greatly appreciated.

Dickytee, The standard kill switch wiring feeds power to the ignition through the switch itself, so normally it indeed has continuity in the wiring. When you press the kill switch the connection is broken and the feed to the ignition is interrupted. It's not such a great system as over time the points in the kill switch can corrode causing a high resistance and lower voltage at the ignition. I tend to wire mine through an A-B relay direct from the ignition switch to the ignition and use the kill switch as a trigger to switch the relay - the relay only uses the kill switch wiring as an earth so isn't voltage sensitive so even a poor earth will still switch it off and if it malfunctions it will generally do so in favour of On rather than OFF.

dave M said:

Dickytee, The standard kill switch wiring feeds power to the ignition through the switch itself, so normally it indeed has continuity in the wiring. When you press the kill switch the connection is broken and the feed to the ignition is interrupted. It's not such a great system as over time the points in the kill switch can corrode causing a high resistance and lower voltage at the ignition. I tend to wire mine through an A-B relay direct from the ignition switch to the ignition and use the kill switch as a trigger to switch the relay - the relay isn't too voltage sensitive so even less than the full 12 volts will still switch it off and if it malfunctions it will generally do so in favour of On rather than OFF.

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Thanks for your reply. Need to clarify, by breaking the circuit are you opening a closed circuit? Or closing an open circuit? It’s positive earth by the way.

dickytee said:

Need to clarify, by breaking the circuit are you opening a closed circuit?

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Yes, when you press the kill button you are interrupting the power feed to the ignition.

Dickytee, I've edited my posting to make it a bit clearer - I hope. I rewire the original kill switch wiring as an interruptible earth to shut off the power going through my relay from the ignition switch to the ignition.

Where do you put/mount this relay and how big is it?

MichaelB it's a standard automotive relay available in most auto parts shops. It's just over an inch or so cubed, with a mounting tab on it. I mount it just above the coil mounting and run a feed wire to it from the ignition switch and then attach the output wire to the electronic ignition module. I then attach another power feed wire to the solenoid trigger circuit with the output of that circuit connected to one end of the wire leading to the kill switch, the other end of the kill switch wire I attach to earth. The relay is NOT an ON/OFF relay, but an A/B relay, which diverts the power from feed A to Feed B. With the ignition switch on the relay automatically sends power to the ignition by virtue of the solenoid trigger circuit being earthed through the kill switch. When I press the kill switch the earth connection is broken and the relay power is diverted to the B output, which has nothing attached to it. The standard design of feeding 12 volts from the ignition switch through the kill switch wire and back out to the ignition is a recipe for trouble as the points corrode and the voltage feed at the coil end of things can drop dramatically.

Kill switch issues should not cause the fuse to blow (unless somethings messed up inside the switch cluster). I had a random fuse blowing situation on my MK2 850...turned out to be the 5 bullet connector block under tank. The rubber block material between different bullets had degraded and was shorting across circuits.

Tornado said:

Kill switch issues should not cause the fuse to blow (unless somethings messed up inside the switch cluster). I had a random fuse blowing situation on my MK2 850...turned out to be the 5 bullet connector block under tank. The rubber block material between different bullets had degraded and was shorting across circuits.

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Thanks. I’m thinking of bypassing the kill switch.