1975 BMW R75/6: Installing Wiring Harness

I documented installation of the main wiring harness on this project and posted it here.

I made a short video to show the routing I used and where the front turn signal, neutral switch, voltage regulator, starter relay, coils, Dyna III electronic ignition, oil pressure switch, neutral switch and rear tail light/turn signal wires go.

Video Link:
–> https://www.youtube.com/watch?v=Wq_ZDRPHVeY

It includes links to two other write-ups: The first describes the wiring connections to the diode board, alternator, points, and starter motor when I replaced the timing chain; The second write-up shows the details about the circuit board connection areas inside the headlight shell and how to connect the right handlebar switch inside the headlight shell.

I hope these write-ups will be helpful when you are installing these components and/or putting a wiring harness back into your bike.

1975 BMW R75/6: Replacing Left Side Handlebar Switch

I had to replace this switch and decided to document “what wire goes where” inside the headlight shell on the circuit board and to the ignition switch and headlight relay.
I also explain how to map information found in various wiring diagrams to the labeled areas on the circuit board. There are some places where things got confusing for me in going between the various published wiring diagram(s) and the circuit board inside the headlight shell, so I hope this material helps others avoid being confused.
You will find this write-up here:

Here are a couple pictures from the write-up.

Broken Left Side Headlight Switch

Broken Left Side Headlight Switch

New Switch Assembly with (8) Wires

New Switch Assembly with (8) Wires

Wiring Circuit Board Inside Headlight Shell [Source: MAXBMW]

Wiring Circuit Board Inside Headlight Shell [Source: MAXBMW]

Green/Black Wire Is A Ground Wire-Goes to Brown Section of Circuit Board

Green/Black Wire Is A Ground Wire-Goes to Brown Section of Circuit Board

1975 BMW R75/6: Rebuilding Master Cylinder & Caliper

This bike uses a single ATE 38 mm caliper (as in the size of the piston inside the caliper, not the size of the caliper shell). In 1976 the ATE caliper was changed to a 40 mm model to improve braking. There was also a change to the master cylinder mounting system resulting in a single hole in the brake fluid reservoir that mounts on top of the master cylinder. Other than these small changes, the work I did applies to all the /5, /6 and /7 models of the ATE caliper and under-the-tank master cylinder.

You can read about how to do this work here:

I had occasion to work on both my 1975 R75/6 and someone else’s 1976 R75/6 at the same time, so there are some pictures of the markings on the 40 mm caliper and the different mounting systems (two hole and one hole) of the brake fluid reservoir.

Some pictures from this write-up are below.

Master Cylinder & Fluid Reservoir Mount Under Gas Tank

Master Cylinder & Fluid Reservoir Mount Under Gas Tank. Note the Evidence of Brake Fluid Leak.

Earlier Style Master Cylinder Fluid Reservoir-Two Holes With Mounting Bracket

Earlier Style Master Cylinder Fluid Reservoir-Two Holes With Mounting Bracket

Later Style Master Cylinder Reservoir-Single Hole With Threaded Sleeve

Later Style Master Cylinder Reservoir-Single Hole With Threaded Sleeve

Earler Two Hole Master Cylinder

Earler Two Hole Master Cylinder

Master Cylinder Piston Assembly Removed

Master Cylinder Piston Assembly Removed

Removing Top Hat From Master Cylinder Piston

Removing Top Hat From Master Cylinder Piston

Master Cylinder Rebuild Kit Parts

Master Cylinder Rebuild Kit Parts

New Master Cylinder Piston with New Rubber Seals Installed

New Master Cylinder Piston with New Rubber Seals Installed

Master Cylinder Installed on Frame Tube

Master Cylinder Installed on Frame Tube

R75/6 Caliper Seal Kit - Source: MAX BMW

R75/6 Caliper Seal Kit – Source: MAX BMW

Caliper Showing Piston and Dust Seal

Front Face of Piston with Center Hole Surrounded by Rubber Dust Seal

A Blast of Compressed Air Removes Piston

A Blast of Compressed Air Removes Piston

Dust Seal Installed in Large Groove in Piston

Dust Seal Installed in Large Groove in Piston

Pulling O-ring On Eccentric Pin With Pick

Pulling O-ring On Eccentric Pin With Pick

Movable Pad with Flat Face of Pad Pointing to the Front

Movable Pad with Flat Face of Pad Pointing to the Front

Fixed Pad Secure with Wire Clip

Fixed Pad Secure with Wire Clip

Caliper With Painted Metal Line Installed

Caliper With Painted Metal Line Installed

1975 BMW R75/6: Replace Rear Main Seal, Oil Pump Cover, O-ring, Refurbish Clutch

I have completed documenting this work for those interested in the parts, tools and procedure used.  You can find my write-ups here.

I did the same work on my R75/5 as well which you will find on my site. The main differences between these projects were using Southland Clutch to refurbish the R75/6 clutch where I replaced the clutch on the R75/5 project, and not damaging the rear crankshaft thrust washer this time. 🙂

This is the first time I used Southland Clutch. I am very pleased with their knowledge of airhead clutches, their courteous and prompt service and the quick turn around at a price about one-half the cost of the new parts. I am adding them to my Resources list.

Engine Out of Frame

Engine Out of Frame Showing Clutch Compression Ring

Small Bolt in Alternator Nose Keeps Crank From Moving Forward

Small Bolt in Alternator Nose to Keep Crank From Moving Forward

Hardened Clutch Install/Removal Bolts, Nuts, Washers

Hardened Clutch Install/Removal Bolts, Nuts, Washers

Removing Every Other Clutch Bolt

Removing Every Other Clutch Bolt with Battery Powered Impact Driver

Friction Disk Uneven Wear: Note Part Number Still Showing on Side Facing Pressure Plate

Friction Disk Uneven Wear: Note Part Number Still Showing on Side Facing Pressure Plate

Cycle Works Flywheel Puller Parts

Cycle Works Flywheel Puller Parts

Old Style Oil Pump Cover with Phillips Head Screws

Old Style Oil Pump Cover with Phillips Head Screws

Evidence of Oil Leaking Past Rear Main Seal

Evidence of Oil Leaking Past Rear Main Seal

Groove Cut in Flywheel by Old Style Seal

Groove Cut in Flywheel by Old Style Seal

Cycle Works Rear Main Seal Puller Parts

Cycle Works Rear Main Seal Puller Parts

Heating New PTFE Seal in 150 F Engine Oil to Soften

Heating New PTFE Seal in 150 F Engine Oil to Soften

Forming Crank Rear Oil Seal on Flywheel Ring

Forming Crank Rear Oil Seal on Flywheel Ring

Tightening Flywheel Bolts on Cycle Works Seal Installation Tool

Tightening Flywheel Bolts on Cycle Works Seal Installation Tool

Flywheel Installed

Flywheel Installed

South Land Clutch Refurbished Clutch Compression Plate

Southland Clutch Refurbished Clutch Compression Plate

South Land Clutch Refurbished Clutch Plate

Southland Clutch Refurbished Clutch Plate

Southland Clutch Refurbished Clutch Plate

Southland Clutch Refurbished Clutch Plate

South Land Clutch Refurbished Pressure Plate

Southland Clutch Refurbished Pressure Plate

3 Clutch Bolts Added with Long Installation Bolts

3 Clutch Bolts Added with Long Installation Bolts

Transmission Ears Aligned With Clutch Housing

Transmission Ears Aligned With Clutch Housing

Refurbished Clutch Installed

Refurbished Clutch Installed