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BMW Alarm Installation

BMW Alarm Installation

By William Scott Hiles
February 1996

I just bought a BMW alarm for my K75S from the BMW dealer in Fredericsburg. Being an electrical engineer I figured I could install it myself. As it turns out, the manual for the alarm is incorrect and was dated 1995. I have written up a summary off how the alarm should be installed for the 75S.


The BMW alarm system is competitively priced to other common motorcycle alarm systems. It consists of two parts that must be purchased: the CPU/sensor unit, and the wiring harness. The alarm for the K series bikes is different from the RS series.

The alarm features:

  • Auto rearm after activation
  • Remote transmitter
  • Two dimensional sensor
  • Starter disable
  • Immediate trigger when key is in the ON position
  • Manual or automatic arm
  • Adjustable sensitivity

The system provides a LED that is mounted to the front steering mount cover to indicate the status of the system. The alarm also has a feature that allows you to know if the alarm has been triggered while you were away. When the alarm is turned off using the remote, the the horn will sound for a long beep and a short beep if the system has been triggered. If it has not, the alarm will emit two short beeps. It also features a 20 second delay for the automatic arming feature to give you time to lock the front front fork and the bags before the alarm arms itself.

The power drain on the battery is stated at 0.02 watts when the alarm is armed but not triggered.


The instruction manual for installation of a BMW alarm system for the K75 motorcycle is incomplete an in error in some cases. The dealer was not able to solve the problems with the manual and so you will need just a little more information to complete the installation.

Remove the gas tank by removing the brass retaining clips from the rear of the tank. These clips prevent the tank from sliding through the rubber mounts between the tank and the frame. After removing the clips, lift the tank up and follow the electrical connection from the tank to find the plastic connector. Separate the connector to disconnect the electrical sensors from the tank. Lift the rear of the tank and slide it backwards till you can get to the vapor hoses on the bottom of the tank. Pull these hoses off. Pull the tank back till it clears the front fairing and disconnect the fuel lines from the front of the tank. Have a towel handy to catch the fuel that is in the line at the time and remove the tank. Set the tank aside.

If you have the ABS system installed, you will need to remove the large connector on the side of the ABS computer under the seat. Remove the seat locking bracket using the small hex wrench from the BMW toolkit. Remove the four retaining screws and pull the plastic mounts off the locking mechanism. Slide the steel bar away from the frame to free the ABS mounting box. Pull the box up and backwards to remove from the bike. This will expose the battery.

The relay box is the plastic box mounted forward of the seat latching mechanism. This box cannot be easily pulled out so just leave it in the bike. Remove the cover.

Remove the negative lead from the battery first, and then remove the positive lead. If you have the original BMW battery, it will have plastic covers over the terminals which can be removed with a small screwdriver.

Free the rear cowling from the bike by removing the four screws under the seat and the two nuts that are inside the cowling. Do not try to remove the cowling completely unless you are willing to disconnect the rear ABS computer and the brake lights.

Finally, remove the covers to your steering mount by removing the two retaining screws in each of the covers.

Make sure that you purchase the long harness (part number 95 00 5 000 120). The K75 doesn’t have room for the alarm CPU below the seat and the long harness will reach the tail section. This harness is about $70.00 so you don’t want to buy the wrong one and have to remove it after you are half way done.

The instruction manual for the wiring harness is incomplete and has an error that will prevent the alarm from working. Additionally, the suggested routing of the harness interferes with the seat locking mechanism so you will want to do it differently. I also suggest not connecting the battery to to the alarm until you have completed all of the wiring.

Using a 3/4 inch drill bit, drill a hole in the relay box near the starter relay in the rear right hand corner. Be careful not to hit the starter relay and set the hole far enough to the right that when the rubber plug of the harness is inserted, it does not interfere with the latching clip for the cover of the relay box.

Use a 1 inch drill bit to drill a hole through the fiberglass base of the rear cowling. You will want to drill through the rounded area as indicated in the drawings in the installation manual. There are rubber mounts that space the rear cowling away from the frame enough that the harness will not be pinched by the frame for this hole. The manual suggests a 3/4 inch hole, but you will never get the large connector through that size hole.

Find a suitable location on the steering mount cover to drill a 1/4 inch hole. (My bike does not have the heated handgrips so I removed the plug for that switch and drilled the hole for the alarm indicator LED in the plug. I prefer this over drilling a hole in the cover above the key.)

The hard part is done. Feed the dash indicator led through the 3/4 inch hole in the relay box and then feed the rest of the wires through. Feed the round white horn connector through first and the rest should go through easily. There is a small 1/4 inch hole in the front rubber stopper of the relay box. Use a small knife to open up this hole and feed the dash LED through this hold. Feed the brown grounding wire that is pulled out of the LED wire casing through the hole also.

The grounding bolt is on the left side of the center frame tube and about half way between the relay box and the front fork. Remove this bolt and attach the BROWN grounding wire from the harness to the bolt along with all of the wires that were previously connected to the frame. Reattach the bolt.

Route the alarm Warning/Status indicator LED along the right side of the frame with the other cables that go to the front dash. Remove the black metal mounting sleeve from the LED. Simply pull on the metal sleeve while pushing on the LED. The two separate fairly easily. Remove the nut on the sleeve and apply some super glue or thread locking compound on the threads near the end where the LED would be. Insert this through the 1/4 inch hole that you previously drilled in the steering mount cover and secure it with the washer and nut. Insert the LED through the sleeve.

Use a tie wrap supplied with the harness to secure the LED wire to the other wires on the front of the steering column being careful to leave enough slack for the full range of motion for the steering column. Test out the slack by turning the front when across the full range. Use two more wire ties to secure the rest of the wire to the frame down the right side of the bike. Pull the slack back into the relay box to avoid it getting pinched when you put the tank back on.

Reattach both covers for the steering mount. Notice that there are two small plastic ears that hold the rear cover against the front cover. Attach the front cover first and route the cables behind it so that when the second cover is attached, the clutch cable and the throttle cables route through the cutouts provided in the second cover.

Remove the screws for the blinker relay in the rear left corner of the relay box. It has two retaining screws. This will make it much easier to locate and patch into the blinker wires.

1. Locate the blue/black wire which attaches to the left blinker circuit. Connect a 3M blue plastic patch on this wire and connect the blue/black wire from the harness to this connector. (Hint, if you have removed the turn signal relay unit, the two wires for the blinkers are in the corner of the connector and are easy to find when you turn the relay over. Trace these wires to a suitable distance from the relay where the wires have some play and attach the 3M patch connector.)

2. Locate the red/blue wire which attaches to the right blinker circuit. Connect a 3M blue plastic patch on this wire and connect the red/blue wire from the harness to this connector. This instruction is in the manual for the short harness but not for the long harness.

3. Locate the green/black wire which attaches to the +12 volt KEY ON circuit. Attach a 3M blue plastic patch on this wire and connect the green/yellow wire from the harness to this connector. (Hint, locate the brown round auxiliary connector in the relay box. The green/black wire has a terminal in this connector and you can patch onto the wire that enters the connector. This connector has 5 wires coming into it.)

This instruction deviates from the manual. The instructions indicate that the green/yellow wire of the wiring harness be connected to the green/yellow wire of the motorcycle. This is incorrect. The rear of the instruction manual provides a description of the wires and this wire should be connected to the +12 volt KEY ON wire. The wiring diagram for your bike indicates that this wire is the green/black wire.

4. The starter relay is in the rear right corner of the relay box. There is a square plastic connector on the side of the starter relay with a brown/red wire and a black/yellow wire. Pull the plastic connector from the relay. Insert a small screwdriver or paper clip into the plastic shell and release the retaining clip for the brown/red wire. Pull this wire out of the plastic connector. Put the plastic connector back onto the starter relay. Find the brown/red male connector from the wiring harness and connect the brown/red wire that was removed from the starter. Find the other female brown/red wire that is attached to the harness and push it into the vacated hole in the connector to the starter relay.

5. Locate the round white connector for the horn inside the relay box. Connect the mating round white connector from the harness so that the keys in the connector match up.

6. Do not connect the white wire of the harness to anything. The wiring diagram indicates that this wire is an instant trigger, but there is no mention of any connector that the bike would have for this function. The dealer indicated that it should just be left unconnected.

The wiring is now complete for the relay box. Replace the cover for the relay box. The instructions indicate that a slot should be drilled opposite of the 3/4 inch hole in the relay box. However, this hole and the harness will interfere with the seat locking mechanism. Route the wires of the harness from the relay box straight down so that they will go between the relay box and the mounting box (for the ABS if present) below the seat latch.

There are two wires that are about 8 inches long for connection to the battery. Connect the red wire to the positive terminal of the battery first. Then connect the brown wire to the negative terminal. The clock on your dash will have to be set now that power has been restored to the bike..

Remount the ABS box and computer for the front ABS system and resecure the locking mechanism for the seat. Plug the ABS cable back into the ABS computer on the left hand side of the bike.

Route the remaining long cable of the mounting harness under the frame in parallel with the main electrical harness for the brake lights (and ABS system if present). If you press on the shell of the existing electrical wires, you can make room for the new harness such that it is not visible from the outside of the bike or from the inside with the seat removed. Push the plastic CPU connector through the 1 inch hold that was drilled in the tail cowling and secure the wire to the frame using the remaining wire ties. Replace the rear cowling by securing the nuts to the bolts for the tail section inside of the cowling and then securing the four bolts in the area below where the seat will mount.

Find the fuse that was in the same bag as the 3M connectors with the CPU and install it into the fuse holder in the alarm harness. The fuse connector should be about 6 inches into the cable behind the relay box.

Test the system before mounting the CPU and sensor. Remove the rubber cover over the hold in the casing for the CPU. Attach the CPU to the wiring harness. The red light inside the box should blink on and off. If this does not happen, then there is probably a problem in the wiring to the battery.

The red light inside of the CPU case is the logic indicator for the sensor. Jiggle the sensor to verify that it is properly connected and working. (Hint, the wiring to the sensor on my system was kinked inside the box and over time broke through the wire casing. The touching wires disabled the sensor. If everything appears to work properly but the sensor doesn’t function, you can open the CPU box by removing the four screws and examine the wire. It clips onto the circuit board for the CPU and can easily be removed for repair.)

Synchronize the CPU with the remote transmitter. The instructions for the alarm are incorrect for the synchronization. You must hold down the red button inside the CPU box till the light on the dash turns red (about 5 seconds) and then while holding down the button, press the first button on the remote transmitter. The alarm will then flash the light on the dash to indicate that it has synchronized. Follow the test procedure in the rear of the manual to verify that the alarm is operating correctly.

Follow the directions in the manual for attaching the double sided tape to the CPU and to the sensor. The sensor can be mounted such that it is parallel to the frame or perpendicular to it. I chose to mount it perpendicular such that it is on the inside right side of the rear cowling just above where the harness enters the cowling through the 1 inch hole. Mount the CPU to the inside top surface of the rear cowling. If you have an ABS system, you can mount it to the bottom of the ABS mount.

Reattach the fuel tank by sliding placing it over the engine and frame. Attach the fuel lines to the front and then slide it into place. Lift it up slightly and attach the fuel vapor lines. (Hint, it is common practice for the BMW dealers to replace the vapor lines with a vapor box outside of california so don’t be alarmed if you do not have the vapor lines.) Double check to make sure that you did not kink the lines and that the lines connect to the front of the crank case. It is easy to pull these off of the front of the crank case. Reconnect the electrical connector for the fuel tank to the electrical system of the bike and push the tank back into place. Push down on the tank so that the rubber mounts push through the fittings on the frame. You may have to use a screwdriver to help them through the frame. Finally, attach the retaining clips to the posts.

Close up the compartment in the rear cowling, attach the seat, and you are done. Retest the system to make sure it works after you have reassembled the bike.

Just one final note. The wire that connects the sensor to the computer for the alarm appears to be very sensitive to kinks and stress. Be careful to make sure that the wire does not vibrate freely and is not under any strain.

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