BMW R75/6 Bad Wiring - Left Turn Signal - Drains Battery

I have the following problem on a 1976 BMW R75/6.

If you turn the ignition key to the first position on. " The front and
back Left turn signal lights come on".

If you turn the ignition key to the second position to start.
AND
You turn the headlight switch to the middle position the "The " The
front and back Left turn signal lights come on again".

If you leave the bike sit with the battery connected and all switches
in the off position. You end up with a short to ground somewhere???
That drains the battery?????

I literally have checked everything except the ignition switch and the
common ground under the frame near the ignition coils. I have checked
and replaced the turnsignal relay and tested the voltage at the
turnsignal relay and turnsignal switch. I have replaced the wireing
harness and switches for the headlight. I have removed the fairing and
inserted a test light bulb on the left side and both front and back
turn signal lights still come on??? So its not in the fairing, its in
the frame. My last resorts are re-constructing/soldering the ground at
the ignition coils which I have replaced both coils.

I have checked the rear brake light assemby and found no wiring
problems,but maybe I should check it again. I cannot get the lens off
the Left rear turn signal because the dim whit that I bought the
motorcycle from RTV'd the lens to the housing.

Anyone with any ideas.

Fossil

 

Are you sure it's not the battery ? If you've got one bad cell the
charging system might be able to bring the voltage up but
it'd quickly drop when the engine stopped. Are you sure it
holds a good voltage when it's disconnected ?

What voltage are you seeing with the engine running at say
3000-4000 RPM ? At idle ? when it's first shut off and after sitting ?

Assuming for the moment that it's the wiring and not
the battery, to check the wiring, I'd disonnect the positive
leads and check for resistance to ground.

If you check the fat lead and see something other than infinite
resistance, you may have a problem in the diode board or
elsewhere in the charging system.

If there's a clock, disconnect the clock before testing.
If you see something other than infinite resistance on the
skinny lead, you might have a problem in the ignition
switch or in a relay. You might also have wires connected
to the wrong terminals.

Actually, from what you're describing, wires running to the
wrong leads sounds like a real possibility. Haynes has some
pretty decent color wiring diagrams which might help you
troubleshoot this.

If there are more than two leads to the + terminal, there's
probably an aftermarket accessory or two on the bike.
Disconnect these and see if it changes.

Best of luck

 

Rob, Part of the problem was that this bike had an after market faring.

There was a bad crimp conntection to the blue/red wire in the wiring
harness with the faring removed and two 12v test lamps installed for
turnsignals. I disconnected the blue/red (left turn signal) from the
connection block behind the headlight and then the turnsignals would
operate correctly. I then replaced or recrimped the connections from
the wiring harness to the fairing. I reconnected the fairing and had
the same old problem again. The wiring harness in the fairing is a real
rats nest. I am in the process of re-wiring it now I hope that finally
fixes the problem. I will let you know. Fossil

 

So were you actually getting a battery drain with the key off ?
That part still seems a little surprising.

Also, on the airheads list I'd bumped into this interesting post
on BMW wiring colors which might be helpful

===========================================

*** This and more will be posted to Airheads.org for future reference.
***


RT = Rot, red
GE = Gelb, yellow
GN = Grün, green
BL = Blau, blue
VI = Violet, purple
GR = Grau, grey
BR = Braun, brown
WS = Weiss, white
SW = Schwarz, black
xx/yy = xx wire's main color with yy stripe

! NOTE !
It was common practice to substitute a different wire color if the
proper one was out of stock, and then "flag" it with the proper
color(s). As the flags' adhesive ages, it dries up and the flags often
slide down the wire out of sight or fall off. If you have an 'odd'
wire, identify it through process of elimination by doing all others
first, double checking with a volt/ohm meter, and then "re-flagging" it
with the proper color. Better still, use heat shrink tubing of the
proper color. ! ALSO ! Some books accidentally transpose numbers or
letters on wiring diagrams (e.g. SW instead of WS, or two 86 terminals
instead of a 85 and a 86).


MAIN Wire Colors
RT -- POSITIVE straight from battery, power to ignition key and starter
relay
BR -- direct to GROUND

GN -- (+) power to most circuits
GR -- (+) power to PARK lights (head, tail, dash, ...)
GN/SW or GR/SW -- same as GN or GR but it's after the 8-amp FUSE


LIGHTS' Wire Colors
GE -- to LOW beam filament
WS -- to HIGH beam filament
GE/WS -- power to HI/LO switch

BL/RT -- LEFT turn signals
BL/SW -- RIGHT turn signals

GR/SW -- TAIL (as above)
GN/RT -- BRAKE light

SW/WS -- turn signal DASH INDICATOR
BL -- D+ from diode board and voltage regulator for GEN light
BR/SW -- NEU light
BR/GN -- OIL light
BR/BL -- BREMSE / BRAKE FLUID light
WS -- HIGH BEAM indicator
GR/SW -- gauge illumination


SWITCH Wire Colors
BR/?? -- wire to SWITCH that completes path TO GROUND
BR/GE -- CLUTCH switch
BR/SW -- NEUTRAL switch
BR/GN -- OIL PRESSURE switch
BR/WS -- to HORNs with grounded bodies
BR/BL -- BRAKE FLUID switch

GN/BL -- engine CUT-OFF/KILL switch that supplies power to ignition
coils
BL/GE -- to ground winding of STARTER RELAY
GN/VI -- trigger for HEADLIGHT RELAY
GN/GE -- TURN SIGNAL relay OUTPUT

 

Rob, I found the problem! The guy who wired this faring, from what Rick
Jones said from Motoelecktric, is that most probably this person was
COLOR BLIND. What I found adds to this assertion. The red/blue wire
for the left turn signal was wired into the grey/black wire of the
parking light circuit. Most likely the man was RED/GREEN color blind.
Jerry

 

Glad you found it. The guy was doing wiring and it hadn't
occurred to him that this color blindness might be a problem ?

Rick is great. The most amazing thing about airhead BMWs
is that you're able to find a fair number of people who actually
have a genyuwine clue what they're talking about when
they advise you.

 

Yes, Rob you are exactly correct. Rick also told the correct milage of
the bike, after he told me the timing chain had stretched!!! When I had
to retard the timing all the way. Odometer is 27k, Rick says the bike
must have at the very least 75k!!!! The odometers are known for their
slippage. I am sending Rick a case of Guiness for his help. I would
like to ask you a question. Even though I will be able to get this
bike on the road. It will eventually overheat from the timing problem
per Rick. Is it really worth it to spend $700.00 at Bob's BMW in
Jessup,MD to fix the timing chain and rebuild the carbs? Since the
parts availability of these bikes is a problem??? Any comments. Fossil

 

I don't see why you think parts availability is a problem.

You can certainly rebuild the carbs yourself for under $50
in parts. Kit from Bing or BMW.

You ought to be able to swap the timing chain as well. The
only possible problem might be the need for a special puller
if you also swap the sprockets. If you only swapped the
chain it's fairly trivial (a couple of hours). If you needed
a puller, I'd start with Ed Korn (you can google to find
his website).

My '88 has about 130,000 on the bike but at about 95,000
I blowed it up real good (slow oil leak) and had to swap in
a short block for about $300. I figure the block now has about
65,000 + total mileage. Sold a cam out of the old block
for about $100 recently.

You ought to check out airheads.org and ibmwr.org.
Very good mailing list and tech tips list.

So in answer to your question, if you are anywhere close to
the S.F. bay area I regret to inform you that the bike is hopeless
and I'll take if off your hands and haul it away at my cost.
I offer to do you this favor only because we are such good friends

If you are in the bay area and wish to persist in foolishly keeping
the bike instead of letting me take it off your hands, you
might check out Ted Porter in Scott's Valley who recently started
an independant shop specializing in these dinosaurs.