lokiNYC
The NGK BPR6ES spark plug is a plug and play IF it has a removable cap on top.
Remove the cap so that just the threads are showing.
Use a screwdriver to pry the metal/rubber spark plug connector up.
Unscrew the existing spark plug using the spark plug socket wrench that came in the tool kit.
Screw the new spark plug in using just your fingers. After it snugs up, use the spark plug socket to tighten the plug about 1/2-3/4 of a turn. (It should give noticeable resistance. If it doesn't, continue to tighten until firm resistance is felt.
Replace the spark plug connector cap pushing it down until it stops. You should hear a "zzzzzip" as the connector moves over the threads.
Your done.
IMO, you really should remove the headlight jumper wire in the casquette to make the light switch work.
Ride with the headlight on but if you get into stalled traffic, move it from the main headlight position to the parking light position.
Here's why:
If I am riding with the headlight on my system voltage is over 13 volts and the battery is being charged.
If I come to a stop with the headlight on, the system voltage drops to 12 volts (or less) and the battery is discharging.
If I ride with just the parking lights on, the system voltage is almost 14 volts and the battery is receiving a nice charge.
If I am stopped with just the parking lights on and the engine idling, the system voltage drops to 12-13 volts so the battery is not being discharged.
Just revving the engine up just a little bit will bring the system voltage back up enough to keep the battery charged.
The grounding wire (black) for the battery actually has 2 wires.
One is a heavy wire that goes to the starter motor housing.
The other, smaller black wire acts as the ground path for ALL of the electrical things on your motorcycle (including the charging circuit).
It is this SMALL wire that causes the problem. On the C5s especially but on the G5 and B5 as well, this small wire can break just below the battery connector.
If it breaks, often it will still touch the other end of the broken wire and things will seem to work normally. Then, it can lose contact and battery charging quits, other things like the horn won't work and the electric starter may refuse to work.
The break usually happens underneath the rubber cover that covers the connection to the battery connector.
Just because a battery is new doesn't mean it can't have problems.
As others have mentioned, the plates can break loose. The internal connections may break. It might not have been fully filled at the factory. It might be really old and sat on a shelf for a year or more.....