Horn / Headlight wiring trouble

My 850 has something odd going on with the horn and headlight. The bike starts and runs fine, but when I hit
the horn button or turn the key to turn on the headlight it kills the engine. Never did this before. Any obvious
places to look for a solution?

I'd loose wires under tail lens and inside headlamp do this but may be short in the horn button as well. Glad you get to enjoy a thinking fella's hobby horse.

I don't believe there is anything wrong with your headlight and horn circuits. It sounds to me that you have a bad wire connection. From what you described I think it is the brown/blue wire between the ignition switch and the battery. Assuming that your battery is ok, I would check all of the terminals, fuse and fuse holder between the battery and the ignition switch. When you check the connectors you need to check not only that they are tight on the electrical component, but the wires also need to be secure within the terminals themselves. Even if you're not using an electrical component such as a Zener diode, 2MC capacitor, etc., the wires still need to be secure inside the terminal. This is because the wire terminals also double as a wire splice.

If all of those wire connections check ok, then I would check all of the red wire connections which are the ground wires. Just like the other terminals the red wires go from various electrical components and double as a splice at these components. So even if an electrical component is disconnected, those terminals still need to be in good condition.

The horn and the headlight are thirsty and they draw a bit of current. What happens when there is a poor connection in the circuit and you have a high current requirement of an electrical load (i.e. horn, headlight), you will get a much greater voltage drop at that bad connection. Which would cause the ignition system to quit working.

Hope this helps,
Pete

Thanks for your reply Pete. I'll do some snooping and see if I've loosened something
when I installed my new battery recently.

Another thing to check would be the ignition switch itself. Of course I would check it after checking the other things I mentioned first. The reason is because getting to the switch terminals is kind of difficult to do. Using an ohmmeter you should have 0 ohms between the number 1 terminal and the other terminals when they are switched on. Another way to check it would be to use a voltmeter. You should read 0 voltage drop between the various terminals that are switched on when the horn and the headlights are on. If you read any voltage at all, that is where your problem is.

When the switch is in the ignition position you would check between terminals number 1 and number 2. When the key is in the headlight switch position number 1, 2, 3 and 4 terminals are all tied together. But you should make all checks from the number 1 terminal.