Further testing has revealed that it is the low beam of the headlight. Now I am looking for ideas on how to isolate it from the wires that go forward into the loom and the wires the go down into the engine case. Any input is greatly appreciated.

Tested the connection. The blue wire is grounded on the front half of the plug (look like it goes forward into the loom). On the other side of the plug (female that goes down into the engine case) the black wire goes to ground. I'm assuming BMW used "black" for the ground wire. So that means my problem is on the front half? The (male) side of the plug?

I have found that with this connector disconnected the High beam lead (at the bulb) is showing that it is grounded. Um guessing that is a problem

I have found that with this connector disconnected the High beam lead (at the bulb) is showing that it is grounded. I amm guessing that might be the problem?

I don't doubt that you have uncooperative harness that is loosing battery power with the ignition in the OFF position, but highly doubt that your "short" is in the Low beam. Using meters for testing can give misleading results, and I am assuming you have fallen into one of those traps.

Issues with Low beam would be on the Yellow wire. A simple test for that might be to place an ammeter between the battery and one of its leads, detect the loss you're describing, then simply unplug the headlamp bulb. Unless the ignition switch has failed internally, all power is cut to the lighting circuits when that switch is OFF. Most failures of the ignition switch are failures to make connection not continue connections, so that doesn't make sense.

However, the charging circuit uses a Blue wire, and in fact (according to a schematic) the only 2 wire connector with both Blue and Black wires runs to the voltage regulator. (The Black wire triggers the starter motor.) If the voltage regulator contacts failed to open with loss of power on Blue, then it might continue to power the alternator field with a low level loss of the type you describe.

I would encourage you to simply try another voltage regulator. Since Bosch was the original supplier all the 3 plug regulators are the same, so borrowing one from a friend's Airhead is the way to go. If you simply can't find one, then you can get a new one off Ebay for a whopping $17 (see item 272655228783). This is a German made after market part that is solid state. If your bike is still using the regulator with the steel can, then this is a definite charging system upgrade. So even if your issue persists, this is still a good purchase. But in all honesty, I think it will help with your problem.

BTW... Brown, not Black, is the system Return wire.

All the best.

Sounds like that's worth a try. I'm reading 2 volts "drain" with the ignition off, enough to drain the battery in about 36 hours. The hi beam (at the bulb connection) white wire shows continuity with ground (ignition off). It reads 13 ohms resistance. So I'm going to try to trace that wire too. Um having difficulty finding where it exists the loom.

Using meters for testing can give misleading results, and I am assuming you have fallen into one of those traps.

What you are reading is merely the resistance of the headlamp bulb itself. The other side of the bulb is connected to Return (what you call "ground") via the Brown wire. So of course you're detecting a "continuity with ground". The headlamp must have a path to ground or it simply won't work, and there, going to the other side of the bulb is a Brown wire.

► If that much power was "leaking" via either the Hi or Low beam, then the headlamp would be glowing dimly after the ignition was turned OFF, but it isn't is it ? So the headlamp is NOT the issue.

► Whereas in the scenario I've presented, loss through the alternator field via the Blue wire cannot be seen becasue the alternator is internal to the machine.

A simple way to test the loss caused by the voltage regulator is to simply place an ammeter between the battery terminal and the battery terminal lead. With the ignition switch turned OFF you should see the loss you've described. Now unplug the 2 position connector with Blue & Black wires. If I'm correct the ammeter will now read zero loss. Plug it back in and the loss returns.

Hope this helps.

Using an ohm meter isn't the way to go for checking for a wiring problem. Ohm checking an unloaded circuit is going to trip you up, for sure. Checking for voltage drop in each circuit will keep you headed in the right direction. If you have a draw, putting a test light BETWEEN the - post of the battery and the - cable will light the light. If it lights, start by pulling fuses, one at a time to determine which circuit is the problem. Once you decide on the circuit start disconnecting load devices until the light goes out. If it is a harness problem, then the voltage drop method is the proper way to check it out.