The rear fender assembly parts are the same on the RS and RT models. There’s quite a lot of hardware involved so I show the order of the hardware for the fender, rear tail light, turn signals, mud flap and license plate bracket.

Here is the link to documentation about the removal of the rear fender assembly.

• 46 BMW 1983 R100RS Remove Rear Fender Assembly

Parts

I replaced some of the hardware with stainless steel parts I got from “The Bolt Guy“. I cleaned up and painted the rusted steel plates used on the inside of the fender to secure it to the frame.

NOTE:
The kit is fairly complete, but not all the hardware used on the 1983 models is included such as the Phillips screws for the rear tail light reflector; only the earlier model, shorter screws are included. 

Video

Here is a video that summarizes this work.

VIDEO: 1983 BMW R100RS Install Rear Fender And Lights

Rear Fender Assembly Components

The picture below shows the components of the rear fender assembly with the exception of the license plate bracket. I opted to not restore this fender. It shows some scars accumulated over it’s 37 year life, but most of them are not visible when the seat, seat cowl and side panels are installed. So I decided to just clean it up and to remind me of the provenance of the bike when I got it.

Here is the license plate bracket and it’s hardware along with the red side reflectors that mount on it.

Install Rear Turn Signals

The turn signal stalk has a hole on the top so the turn signal wires can be routed inside the stalk to each side.

The rear sub-harness has all the wires for the turn signals and the tail and stop lights. Toward the rear of the harness, the four turn signal wires branch off from the main sub-harness.

Each turn signal has a separate BROWN ground wire. The left signal has a BLUE–Red wire and the right signal has a BLUE-Black wire. I mark the left side of the stalk with a piece of tape so I don’t get confused which wires go to which end of the stalk.

I can push the two wires that go to each side through the center hole and out the end of the tube without using a pull string.

To make it a little easier to thread the wires, I don’t install the turn signal housings onto the ends of the stalk until I thread them into the housing. There is a notch cut on the end of the stalk. The mounting bracket inside the turn signal housing has a finger the fits into the notch to keep the housing from turning on the end of the stalk. After I thread the wires into the housing, I slip the housing onto the end of the stalk, orient the slot with the finger and then tighten the two screws that secure the clamp inside the housing.

I attach the wires to the terminals on the back of the turn signal reflector. The power connects to the terminal that goes to the center of the bulb and the BROWN ground wire connects to the terminal that goes to the side of the bulb base.

I insert the reflectors into the housing and attach the yellow lens using the two Phillips head screws being sure the hole in the reflector is on the bottom. This lets condensation and water escape from the housing.

I’ll wait to install the wires that go to the tail and stop lights inside the rear light housing until I mount the fender.

Install Rear Fender

The front of the rear fender attaches to a set of pins on the rear of the battery bracket.

The pins on the rear of the battery box have a habit of wallowing out the holesin the front of the rear fender leading to cracks and that can  let the fender rattle. I use a small diameter rubber hose inside the holes in the fender and push them onto the pins to eliminate any rattles and to treat the fender holes kindly

I insert the fender onto the battery box pins.

The frame mounting hardware differs for each bracket.

The rear bracket is where the under-the-seat tool box is mounted so the bolts are longer and there is a second steel strap that goes inside the tool box to secure it.a front and rear bracket on the rear sub-frame and

I attach the fender to the front bracket. The metal strap goes on the inside of the fender. The heads of the hex bolts are on the inside of the fender along with the two large flat washers.

When I push the bolts through the fender, I put the rubber gasket on the bolt. This helps keep it from falling out as I thread the other bolt up from the bottom. The gasket sits between the top of the fender and the bottom of the front sub-frame bracket. I put the flat washer and lock nut on the the end of the bolt to secure the fender to the front bracket.

The rear bracket hardware on the inside of the fender goes on the same was as the hardware on the front bracket.

The rubber grommets fit between the top of the fender and the bottom of the tabs on the rear bracket. It temporarily install the lock nuts to keep the bolts from falling out.

I put the rear tool box over one bolt, then the strap and a lock nut threaded just a turn. Then I install push the other bolt through the hold in the tool box and the strap and install the lock nut. I tight up the lock nuts to secure the fender and tool box to the rear fender bracket.

Install Turn Signal and Tail Light Assembly

The stalk mounting bracket lies flat on the shelf at the rear of the fender. The stalk tube extends downward above the lip on the end of the fender. The tail light assembly fits on top of the stalk’s bracket.

NOTE:
Some of these pictures were taken on the bench to make it easier to see the details.

The tail light housing and turn signal stalk assembly use the same hardware inside the fender, but there are not rubber grommets or lock nuts. The turn signal stalk sits flat on the shelf at the end of the rear fender. The tail light housing is on top of the stalk bracket and the sub-harness is pushed against the bottom on the tail light housing by the stalk bracket. The the bolts are secured inside the tail light assembly with wave washers and nuts.

I insert the wires of the rear sub-harness for the rear tail light through the hole in the bottom of the tail light housing and secure the rubber grommet in the hole.

I install the steel strap and hardware as I did for the front and rear fender brackets. I insert one bolt through the hole in the turn signal stalk and while holding it from the bottom push it through the hole in the tail light housing and then put the wave washer and nut loosely on the end of the bolt until I get the other bolt installed.

The tail light reflector has two bulbs, a 5 watt parking light bulb that’s on the bottom and a 21 watt brake light bulb that’s on the top. The reflector is marked with these wattage next to the bulbs.

I install the GREY-Black wire on the center terminal of the bottom bulb, the GREEN–Red wire on the center terminal of the bottom bulb and the two BROWN ground wires on the terminals facing each other in the center of the reflector.

The rear sub-harness routes on the outside of left side of the rear fender. It is secured with three plastic clips that fit into holes in the fender. When the strap of the clip is looped over the sub-harness one end snaps into the cylinder which fits into the hole in the fender. When I get the straps secured around the sub-harness, I connect the sub-harness into the plug on the rear of the main wiring harness.

NOTE:
These straps are no longer available so treat them carefully.

Attach Mud Flap

This bike came with a mud flap. It is secured to the bottom of the rear fender on the inside with four bolts, grommets, flat washers and lock nuts. The flat washer and lock nut go on the inside of the fender and the bolt head and grommet are on the outside.

Install License Plate Bracket And Side Reflectors

The license plate bracket has side brackets for the red side reflectors.

The side reflectors have a long stud that fit into a hole on the side bracket. they are secured with a flat washer and lock nut.

The license plate bracket attaches to the fender with three oval head Phillips head bolts that are secured on the inside of the fender with a flat washer and lock nut. The bottom bolt also fits through a hole in the mud flap.

All Done

I tested the lights and everything works.

I installed the rear wheel and brake. It’s starting to look like a real motorcycle again.