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Couple of questions for the group-1988 R100RT. Owner's manual doesn't show the accessory plug or mention it anywhere...wondering if it was added to this bike after the fact? Anyone know offhand what year/model the accessory plugs were added?

Also, my plug appears to be dead...shouldn't it be hot all the time so that a battery tender can be used? I haven't tested it yet w/engine running, but at 'off' and ignition 'on' position there's no juice to it....

I think that it is aftermarket. Check the wiring. Wire it directly to the battery terminals. Use NO-OX (grease) on the terminals.

Could be for hooking up a sidecar tail light. Check for voltage with the headlight on.

If it's the accessory plug that attaches on the left under the pillion seat, it's probably the BMW optional extra kit. If so it should be constantly live and has its own fuse in a 'on-line' 'torpedo' fuse holder. If it is the same as the earlier type, it connects direct to the battery.

Rob

I have two spare plugs on my '89 RT loom above the air box, a two wire white plug and a blue plug - don't you know!

In the spirit of closure for this thread, this issued was solved with your collective help....seems the accessory plug is an add-on accessory on this 88 R100rt. It was hot wired to the battery in its original install by PO...I traced the wiring till I found the well-concealed in-line fuse holder inside which was a blown torpedo fuse. Case solved!

FWIW,

The accessory socket is intentionally wired direct to the battery for three resons:

1. So that it can be used to trickle charge the battery.
2. So that the battery can be used as a power source when the bike isn't switched on.
3. To avoid overloading the ignition switch and bike wiring should there be a heavy current drain plugged in.

If you're worried about this, the best solution is to fit a reasonably heavy duty switch in the circuit, mounted out of the way, possibly under the seat, so that you can isolate the socket at will. Never felt the need to do it myself but it wouldn't be hard.

Rob

Rob Frankham wrote:FWIW,

The accessory socket is intentionally wired direct to the battery for three resons:

1. So that it can be used to trickle charge the battery.
2. So that the battery can be used as a power source when the bike isn't switched on.
3. To avoid overloading the ignition switch and bike wiring should there be a heavy current drain plugged in.

If you're worried about this, the best solution is to fit a reasonably heavy duty switch in the circuit, mounted out of the way, possibly under the seat, so that you can isolate the socket at will. Never felt the need to do it myself but it wouldn't be hard.

Rob

Or put a relay onto its isolated circuit. That would require running one more thin wire, but not too much more trouble. Personally, I much prefer it live all the time, as I have a Battery Tender adapter that plugs into the socket.