First, sweet bike!
Now - there's no "accessory" position on the normal key switch. There's OFF - ON - PARK.
Off is obvious.
On is for riding, all circuits are powered.
Park turns the tail light on (and some country's bikes also have an extra small clear bulb inside the headlight that throws a feeble light from the front).
The wire in your picture is just an extra ground, you can use it for a three wire signal flasher if desired. I've never seen it used for anything from the factory.
Thera are a few general steps to getting a long-stored bike like this to go:
- clean ALL the connectors in the wiring harness. Basically remove the gas tank and headlight, and unplug each bullet and gently clean the male and female ends with alcohol (if pretty clean already) or brasso (if pretty grungy, but get the brasso off afterward with alcohol). The smear a bit of dielectric grease on each end and reconnect. Clean the fuseholder contacts and the ends of the fuses. Clean the multi-wire connector block as well, each spade terminal can be cleaned much like the bullets. There may be some connections beneath the left side engine cover, going to the alternator and the neutral switch. This is worth checking, those alternator wire connections are infamous for overheating and failing because they became dirty and corroded. (disconnect the battery before dicking around with the wiring)
- get some contact cleaner spray and clean the ignition switch contacts - shoot some spray into the switch block end of the assembly and then switch it on and off a few dozen times.
- replace the battery. it's junk after 30 years.
- drain the gas tank, you can add the ancient fuel to a car tank if you're sure it's unleaded but probably toss it out (how? I dunno... I like to burn the stuff off but that does tend to attract sireny fire trucks when I do). Old gas will not burn properly. Open the carb drain screws and see what comes out. You should fill and drain all the bowls a few times with clean gas before attempting to start the bike, removing the bowls and seeing the condition in there is a great idea but also a pain in the butt. I expect to remove the carb stack and do some major goop removal when reviving old bikes though - that is, as a rule, unavoidable. With the gas tank empty, have a look inside with a flashlight (not a good place to use a flame for light) to check for rust. Water tends to collect at the very bottom, and can severely rust the metal. Some rust spots is OK, but if you see cancerous patches at the bottom, be careful as the metal may be tissue thin or you might have only paint holding the fuel in.
- check the air filter. Bugs and mice like to eat the paper and or live in there.
- change oil. drain the tank and sump, fill tank with good new motorcycle oil. synthetic is best, in my opinion, but any decent bike oil will be fine. Avoid car engine oils.
- check the spark plugs. They should be fairly clean if the bike is going to start without a leg-killing kick marathon. Check the ignition works by taking one plug out either #1 (left) or #4 (right) and holding it against the engine metal while kicking over - ignition and kill switches on. You should see a fat blue spark. Reinstall the plug and repeat with either #2 or #3 - inside left and right. Don't take all the wires off and check one for spark - the system sparks through two plugs with each (of two) coil so you need one in to check that coil. #1 and #4 are on one coil and #2 and #3 are on the other coil.
Once you have a spark, fresh oil, and gas in the carbs... try and start it. If it runs at all, sweet! If it actually idles fairly well and revs when you crank the throttle... wow!
Now you have to check a few things before trying to ride.
#1 - brakes - pretty weak if you take your first test ride and crash immediately or go straight into traffic and get killed because there's no brakes. The front disk will probably be seized, it's pretty easy to service though. The rear brake is probably fine but may be grabby from the drum rusting up a bit.
#2 - tires. You need new tires. It doesn't matter if they look new, 30 year old tires are 25 years past being usable. For a quick spin around the block you can risk them but you may end up with the bike sliding out under because of the rock hard slippery tires.
