2020 F750GS Brake light wire location/color code?

[EricV]

I am in the middle of installing an Admore 11" rear light bar on my wife's '20 F750GS and can't locate the plug or wiring for the taillight.  Inside the rear storage area are the turn signal wires, (two wire plugs, one on each side), the harness w/o a plug running to the license plate light that appears to just be two wires, (presumably 12V and Gnd), and two plugs, one 4 wire and one 6 wire.  With both of those plugs un-plugged, the brake and tail light still function.  Leaving me at a loss as to where the heck the brake/tail wires are...

 

Any assistance from someone in the know would be appreciated.  I read conflicting info on color codes and don't see those color wires on either plug.  And I can't locate the wires from the brake light at this point w/o some more removal of plastic.

 

Thanks!

[dirtrider]

16 hours ago, EricV said:

I am in the middle of installing an Admore 11" rear light bar on my wife's '20 F750GS and can't locate the plug or wiring for the taillight.  Inside the rear storage area are the turn signal wires, (two wire plugs, one on each side), the harness w/o a plug running to the license plate light that appears to just be two wires, (presumably 12V and Gnd), and two plugs, one 4 wire and one 6 wire.  With both of those plugs un-plugged, the brake and tail light still function.  Leaving me at a loss as to where the heck the brake/tail wires are...

 

Any assistance from someone in the know would be appreciated.  I read conflicting info on color codes and don't see those color wires on either plug.  And I can't locate the wires from the brake light at this point w/o some more removal of plastic.

 

Thanks!

Afternoon EricV

 

I don't have a BMW 2020 750GS wiring diagram but will assume it operates like the earlier 700/800 GS bikes.

 

The  tail light & brake light on those use a single power feed and a single "low" wire (basically a ground wire) to the rear light that has a  pulse-width modulated voltage input.

 

For the tail light, the current going to the rear tail/brake bulb is constantly pulsed on & off with the intent of maintaining about 8 volts (averaged) to the rear light (this gives  a dimmer light for tail light). Then when brakes are applied that same  (single wire) to the rear light is pulled high to around 12 volts & that gives the rear light a brighter brake light. 

 

Hooking up an add-on light bar can be difficult due to the single power wire with that pulsed tail light current. Some that contain LED's CAN be made to work with some creative connection, others  just won't work,  or (even if)  they can be made to work will trip the continuous dashboard light-out warning system .  

 

My first suggestion to you is to call the tec help line of the light bar you are trying to install & ask them (IF) it will work on the newer BMW  canbus / linbus motorcycles.  At least start with that. Otherwise you can experiment with connecting that to your pulse width modulated rear single-input  light wire (PM me for help with this).

 

There are a number of aftermarket add-on rear lights that will work with your pulsed rear light system (they usually say canbus compatible). Actually has noting to do with the canbus system but that is the way they seem to differentiate the newer pulsed one-wire systems.  

 

 

[EricV]

Sadly, the F750s are different in several ways.  Three wires is what I've been told, ground, tail and brake instead of the two wire on the earlier gen, (ground and tail/brake).  The Admore light bar was previously on my wife's F650GS  K72 twin, so I've been down that road.  It worked fine on that bike, btw.  But I didn't install it either.

 

And thank you, I am aware of the Can bits and specific add on lights.  Admore says their lights are also CanBus functional since '08.  I have a info request in with them at the moment as well.

 

This particular version of the light bar uses a brake signal as a trigger, not as power feed.  It does require a separate 12v switched power source, which I may try to take from the license plate light wire.  I tested it with 12V from the battery and signals work as they should on the light bar and bike.   In regards to the warning light, been there on other applications with other BMWs, so I do understand that issue.  I *think* this particular light is low draw enough to not cause that issue.  Time will tell, once I find the brake light wire.

 

Thanks for taking the time to respond.  

[dirtrider]

1 hour ago, EricV said:

Sadly, the F750s are different in several ways.  Three wires is what I've been told, ground, tail and brake instead of the two wire on the earlier gen, (ground and tail/brake).  The Admore light bar was previously on my wife's F650GS  K72 twin, so I've been down that road.  It worked fine on that bike, btw.  But I didn't install it either.

 

And thank you, I am aware of the Can bits and specific add on lights.  Admore says their lights are also CanBus functional since '08.  I have a info request in with them at the moment as well.

 

This particular version of the light bar uses a brake signal as a trigger, not as power feed.  It does require a separate 12v switched power source, which I may try to take from the license plate light wire.  I tested it with 12V from the battery and signals work as they should on the light bar and bike.   In regards to the warning light, been there on other applications with other BMWs, so I do understand that issue.  I *think* this particular light is low draw enough to not cause that issue.  Time will tell, once I find the brake light wire.

 

Thanks for taking the time to respond.  

Evening EricV

 

If it is in fact a 3 wire system (tail, brake + ground) that seems like a big step backwards but I suppose possible. 

 

Should be easy enough to figure out. I believe the 750 tail light assembly is held in place with 3 "E" clips so if you can access & remove those the tail light assembly should pull free. That should allow you to unplug the connector.

 

Then just put your voltmeter on the 20V dc scale, ground one lead of your voltmeter, then touch the other lead to all the wires in the connector one by one  while someone uses the brake pedal with the key on. 

[EricV]

Yes, I'll need to disassemble the bike to sort this out.  I'll report if what I've been told about 3 wire Vs 2 wire is correct, of if it's a similar 2 wire set up as the previous Gen of F series GS bikes.  These are made by Lorcin, not Rotax/BMW, so who knows?

[EricV]

I was able to get the following info from Admore Lighting about the 2020 F750GS wire colors and install of their current light bar.  Hopefully this will help someone else in the future.  I still have not discovered the location of the tail light plug, but have not had the time to disassemble the bike yet.

 

AdMore Light Bar	Function	2020 BMW F750GS
RED + BLUE	Switched 12V	Accessory Plug or  Red with Green stripe
PURPLE	Brake Light	Gray with Black stripe
GREEN	Turn Signal (Right)	Blue with Black stripe
YELLOW	Turn Signal (Left)	Blue with Red stripe
BLACK	Ground	Brown

 

[dirtrider]

1 hour ago, EricV said:

I was able to get the following info from Admore Lighting about the 2020 F750GS wire colors and install of their current light bar.  Hopefully this will help someone else in the future.  I still have not discovered the location of the tail light plug, but have not had the time to disassemble the bike yet.

 

AdMore Light Bar	Function	2020 BMW F750GS
RED + BLUE	Switched 12V	Accessory Plug or  Red with Green stripe
PURPLE	Brake Light	Gray with Black stripe
GREEN	Turn Signal (Right)	Blue with Black stripe
YELLOW	Turn Signal (Left)	Blue with Red stripe
BLACK	Ground	Brown

 

Morning  EricV

 

Thanks, that seems to show only one wire going to the brake light bulb & no separate tail light wire. For reference, the 800GS is a single wire for brake & tail & that uses a gray/back/yellow wire. 

 

But just to be confusing if you look closely at the tail light picture below is seems to show a 2.5W brake light & a .25W tail light inside?  The connector looks to be a 4 pin but BMW doesn't always use all the pins in a connector  socket.

 

I think your rear tail light harness plug plugs directly into the front of the tail ight housing. (see picture below)

 

I'm not sure on the 2020 F750GS but the older "F" bikes had a removable flap, or door, (remove a screw) on the underside of the very rear of the rear inner fender liner (just above & behind the rear tire). 

 

I believe that your tail light assembly is held in place by an E-clip like clip on each of those 3 plastic pins. 

[EricV]

You are quite correct.  After removing the rear rack, which required removing the Shad top box plate and it's adapter, then the panel beneath the rack with it's four bolts, I have access to the tail light and could remove the top e-clip and perhaps unplug the tail light if necessary.  Moot, since that wouldn't get me what I wanted, but I am able to see down inside the hole there and identify the three wires to the tail light.  Brown is ground, then white with red trace, (tail), and grey or light blue with yellow dashes, (brake).

 

The harness that goes under the tool tray can be un-taped to access these three wires and the two license plate light wires, (which are taped together on their own).

 

No joy so far in getting the Admore light bar to work for brake light.  Turn signals work fine and tail light works fine if you tap the license plate 12V wire as your switched 12v source, but with the brake light wire tapped, it just shuts down the Admore bar the moment you touch the brakes.

[dirtrider]

11 minutes ago, EricV said:

You are quite correct.  After removing the rear rack, which required removing the Shad top box plate and it's adapter, then the panel beneath the rack with it's four bolts, I have access to the tail light and could remove the top e-clip and perhaps unplug the tail light if necessary.  Moot, since that wouldn't get me what I wanted, but I am able to see down inside the hole there and identify the three wires to the tail light.  Brown is ground, then white with red trace and grey or light blue with yellow dashes.

 

The harness that goes under the tool tray can be un-taped to access these three wires and the two license plate light wires, (which are taped together on their own).

 

No joy so far in getting the Admore light bar to work for brake light.  Turn signals work fine and tail light works fine if you tap the license plate 12V wire as your switched 12v source, but with the brake light wire tapped, it just shuts down the Admore bar the moment you touch the brakes.

Afternoon Eric V

 

Seeing as you have that grey (or light blue) with yellow dashes wire tapped you might put a voltmeter on that wire to see if it is pulse width modulated (about 8v with engine running & 12v or so when you tap the brake). 

 

If it IS just a simple 12v (ON for brake & OFF for no brake) then your Admore bar is probably overloading the brake light circuit.

The workaround for that is to probably install small power relay (small enough pull-in coil load  to not effect the brake circuit) then have that relay trigger 12v on & off from another source into your Admore bar (like from the  license plate light circuit) or from fused battery direct.

[EricV]

I'll see if I can get a reading on that with the DMM.  A test light grounded to the battery neg terminal simply caused the OEM brake/tail lights to stop functioning and go dark the moment I touched the test light probe to the gray w/yel trace wire.

[dirtrider]

5 minutes ago, EricV said:

I'll see if I can get a reading on that with the DMM.  A test light grounded to the battery neg terminal simply caused the OEM brake/tail lights to stop functioning and go dark the moment I touched the test light probe to the gray w/yel trace wire.

Afternoon Eric V

 

Wow, that circuit is super sensitive. 

[EricV]

I had a chat with Admore and discovered my issue was as some of you suspected, overloading the circuit.  I did not think the LED light bar would overload the license plate light circuit, but I was wrong.

 

So, on my old circa 2011 Admore light bar the wiring goes as such:

 

Red - 12V switched - I used the Red w/blue trace wire at the 7.5A fuse, (the pair of fuses that are behind the battery area in a blank plug cap.)  See pictures.

Brown - Brake light - Grey w/yellow dashes. (found in the taped loom that goes down under the tool tray through a hole and is visible from below going to the license plate light. )

 

Green - Right Turn signal (blue w/white trace wire (part of the two wire connector on the Right side of the tool tray that is brown, (gnd), and blue, (12v) to a black connector clipped to the side of the tool tray.

Orange - Left Turn signal  (blue w/white trace wire (part of the two wire connector on the Left side of the tool tray that is brown and blue wires to a black connector clipped to the side of the tool tray.

Purple** - Ground

Black - Ground

 

** The purple wire must be grounded or the light will remain in test mode.  The purple and black can be connected to either of the brown ground wires used in the turn signals.  This worked fine with both wires together on one turn signal ground wire.

 

I have no idea with the 4 and 6 wire plugs at the back of the tool tray go to.  I can't identify a 12v source in any of those pins.  The small two wire plug that I think is the alarm plug for those bikes with that option doesn't appear to have 12v power.

 

The two fuse plug forward of the tool tray area has a 10A fuse circuit that is hot all the time and a 7.5A fuse circuit that is hot with accessory and as is typical for BMW turns off after 45-60 seconds once the bike is turned off.  I chose to tap the leg of the 7.5A fuse circuit for my switched 12v source.

 

Note that I did tidy up the wiring after I knew it all worked.    And I used Posi-Taps for all my connections.

 

This works as designed and Beautiful Wife is now happy with having better/more light action off the back of the bike.

[dirtrider]

12 hours ago, EricV said:

I had a chat with Admore and discovered my issue was as some of you suspected, overloading the circuit.  I did not think the LED light bar would overload the license plate light circuit, but I was wrong.

 

So, on my old circa 2011 Admore light bar the wiring goes as such:

 

Red - 12V switched - I used the Red w/blue trace wire at the 7.5A fuse, (the pair of fuses that are behind the battery area in a blank plug cap.)  See pictures.

Brown - Brake light - Grey w/yellow dashes. (found in the taped loom that goes down under the tool tray through a hole and is visible from below going to the license plate light. )

 

Green - Right Turn signal (blue w/white trace wire (part of the two wire connector on the Right side of the tool tray that is brown, (gnd), and blue, (12v) to a black connector clipped to the side of the tool tray.

Orange - Left Turn signal  (blue w/white trace wire (part of the two wire connector on the Left side of the tool tray that is brown and blue wires to a black connector clipped to the side of the tool tray.

Purple** - Ground

Black - Ground

 

** The purple wire must be grounded or the light will remain in test mode.  The purple and black can be connected to either of the brown ground wires used in the turn signals.  This worked fine with both wires together on one turn signal ground wire.

 

I have no idea with the 4 and 6 wire plugs at the back of the tool tray go to.  I can't identify a 12v source in any of those pins.  The small two wire plug that I think is the alarm plug for those bikes with that option doesn't appear to have 12v power.

 

The two fuse plug forward of the tool tray area has a 10A fuse circuit that is hot all the time and a 7.5A fuse circuit that is hot with accessory and as is typical for BMW turns off after 45-60 seconds once the bike is turned off.  I chose to tap the leg of the 7.5A fuse circuit for my switched 12v source.

 

Note that I did tidy up the wiring after I knew it all worked.    And I used Posi-Taps for all my connections.

 

This works as designed and Beautiful Wife is now happy with having better/more light action off the back of the bike.

 

Morning EricV

 

Good job in getting this figured out. All looks good (except those darn Posi-Taps). Most of those things are not waterproof & can eventually cause issues as they can allow moisture to wick into your wire harness. Yours are somewhat protected under the seat area but can still eventually cause issues if  salted road water, or even water-softener water  finds it's way to (then into) those Posi-Taps, then into the wire strands. 

 

You might want to think about sealing those Posi-Taps with liquid tape or a silicone sealer. 

 

 

[EricV]

Thanks for your insightful comments.  My first choice would be to disassemble the connectors and solder a new wire at the existing connector, then re-pin the connectors.  I'm not going to do that for a silly LED light bar.  And I'm not going to cut into the OEM harness either, so that left me with some form of wire tap.  The Posi-taps are a small step up from the fold over versions, but I do agree with your comments.  I've not had issues with them for long term use.  Living in rainy states and dry ones.  Thankfully I don't live near the ocean or in a state that salt the roads.  The last install of this light bar lasted 115k miles w/o issue.  If I get that from this install, it'll do.    Reduce, re-use, recycle...