Trunk Lights Always On + No Alarm Arming

[macmac80210]

I am having a strange issue with my trunk hatch. The lights are always on, as if the car thinks that the door is always open. As a result, the alarm will not arm when I lock it, because the car thinks that the door is open. This is getting very annoying for driving at night, as it makes it impossible to see out of the back window. I think that the car thinks that the door is open, even though it is firmly latched. Does anyone have any suggestions to remedy this, besides taking out the bulbs in the trunk.

[racingbmwm3]

Sounds like the microswitch in the latch is going dead, or a loose wire.
this is the part number from realoem for the latch.
51248408492

First test, easy one, open the door, then use a small screwdriver or similar to manually close the latch, all the way, 2 clicks. Do the lights go off now? If so, your latch isn't getting closed all the way. Check alignment of striker plate and the bump stops.
If the light is still on, check the electrical. You'll need to remove some trim to access the electrical portion of the latch.
I don't have diagrams in front of me, but I'm thinking there should be 4 wires going to the latch, 2 larger ones for operating the latch, and 2 smaller ones for the latch position sensor. Or maybe it's two plugs, and the plug with the 2 smaller wires is the one to be tested. First, press the button to open the door which will release the latch back to its open position. Next, unplug the connector that has the 2 smaller wires. Now measure the wires for voltage, I'm guessing 5V (maybe 12V) should be read across the pins while the car is awake. Next, leaving the latch unplugged, measure the resistance (or continuity, either works) of the latch itself (NOT THE CAR WIRING) across the two pins that correspond to the two smaller wires. I'm guessing this should read either infinity or open circuit since the latch should be open. Next, manually close the latch (again, all the way, 2 clicks) and measure for resistance/continuity again. If the switch is working, then the reading should be around 0.5 Ohms, or closed continuity. Double check that you are reading the correct 2 pins. If the latch reads the same when its open or closed, then you need a new latch. If the switch tests fine, and the wiring has voltage, your General Module must be having issues....
If this is the only electrical issue you are currently having, I'm 90% sure its the latch. Its best to always test that stuff before replacing as most shops will not accept returns for electrical parts.

[racingbmwm3]

Sounds like the microswitch in the latch is going dead, or a loose wire.
this is the part number from realoem for the latch.
51248408492

First test, easy one, open the door, then use a small screwdriver or similar to manually close the latch, all the way, 2 clicks. Do the lights go off now? If so, your latch isn't getting closed all the way. Check alignment of striker plate and the bump stops.
If the light is still on, check the electrical. You'll need to remove some trim to access the electrical portion of the latch.
I don't have diagrams in front of me, but I'm thinking there should be 4 wires going to the latch, 2 larger ones for operating the latch, and 2 smaller ones for the latch position sensor. Or maybe it's two plugs, and the plug with the 2 smaller wires is the one to be tested. First, press the button to open the door which will release the latch back to its open position. Next, unplug the connector that has the 2 smaller wires. Now measure the wires for voltage, I'm guessing 5V (maybe 12V) should be read across the pins while the car is awake. Next, leaving the latch unplugged, measure the resistance (or continuity, either works) of the latch itself (NOT THE CAR WIRING) across the two pins that correspond to the two smaller wires. I'm guessing this should read either infinity or open circuit since the latch should be open. Next, manually close the latch (again, all the way, 2 clicks) and measure for resistance/continuity again. If the switch is working, then the reading should be around 0.5 Ohms, or closed continuity. Double check that you are reading the correct 2 pins. If the latch reads the same when its open or closed, then you need a new latch. If the switch tests fine, and the wiring has voltage, your General Module must be having issues....
If this is the only electrical issue you are currently having, I'm 90% sure its the latch. Its best to always test that stuff before replacing as most shops will not accept returns for electrical parts.

[puddinboo]

also check for broken wires going to trunk maybe broken?

[racingbmwm3]

Sounds like the microswitch in the latch is going dead, or a loose wire.
this is the part number from realoem for the latch.
51248408492

First test, easy one, open the door, then use a small screwdriver or similar to manually close the latch, all the way, 2 clicks. Do the lights go off now? If so, your latch isn't getting closed all the way. Check alignment of striker plate and the bump stops.
If the light is still on, check the electrical. You'll need to remove some trim to access the electrical portion of the latch.
I don't have diagrams in front of me, but I'm thinking there should be 4 wires going to the latch, 2 larger ones for operating the latch, and 2 smaller ones for the latch position sensor. Or maybe it's two plugs, and the plug with the 2 smaller wires is the one to be tested. First, press the button to open the door which will release the latch back to its open position. Next, unplug the connector that has the 2 smaller wires. Now measure the wires for voltage, I'm guessing 5V (maybe 12V) should be read across the pins while the car is awake. Next, leaving the latch unplugged, measure the resistance (or continuity, either works) of the latch itself (NOT THE CAR WIRING) across the two pins that correspond to the two smaller wires. I'm guessing this should read either infinity or open circuit since the latch should be open. Next, manually close the latch (again, all the way, 2 clicks) and measure for resistance/continuity again. If the switch is working, then the reading should be around 0.5 Ohms, or closed continuity. Double check that you are reading the correct 2 pins. If the latch reads the same when its open or closed, then you need a new latch. If the switch tests fine, and the wiring has voltage, your General Module must be having issues....
If this is the only electrical issue you are currently having, I'm 90% sure its the latch. Its best to always test that stuff before replacing as most shops will not accept returns for electrical parts.

[macmac80210]

Originally Posted by racingbmwm3

Sounds like the microswitch in the latch is going dead, or a loose wire.
this is the part number from realoem for the latch.
51248408492

First test, easy one, open the door, then use a small screwdriver or similar to manually close the latch, all the way, 2 clicks. Do the lights go off now? If so, your latch isn't getting closed all the way. Check alignment of striker plate and the bump stops.
If the light is still on, check the electrical. You'll need to remove some trim to access the electrical portion of the latch.
I don't have diagrams in front of me, but I'm thinking there should be 4 wires going to the latch, 2 larger ones for operating the latch, and 2 smaller ones for the latch position sensor. Or maybe it's two plugs, and the plug with the 2 smaller wires is the one to be tested. First, press the button to open the door which will release the latch back to its open position. Next, unplug the connector that has the 2 smaller wires. Now measure the wires for voltage, I'm guessing 5V (maybe 12V) should be read across the pins while the car is awake. Next, leaving the latch unplugged, measure the resistance (or continuity, either works) of the latch itself (NOT THE CAR WIRING) across the two pins that correspond to the two smaller wires. I'm guessing this should read either infinity or open circuit since the latch should be open. Next, manually close the latch (again, all the way, 2 clicks) and measure for resistance/continuity again. If the switch is working, then the reading should be around 0.5 Ohms, or closed continuity. Double check that you are reading the correct 2 pins. If the latch reads the same when its open or closed, then you need a new latch. If the switch tests fine, and the wiring has voltage, your General Module must be having issues....
If this is the only electrical issue you are currently having, I'm 90% sure its the latch. Its best to always test that stuff before replacing as most shops will not accept returns for electrical parts.

Thank you for the extensive reply. I opened it up, and one of the wires was severed. I did a little fix, and everything is back and working great. Thank you so much for the help.

[puddinboo]

macmac where was the wire broken? just incase someone else has this problem they would look there first.

[macmac80210]

Originally Posted by puddinboo

macmac where was the wire broken? just incase someone else has this problem they would look there first.

The previous owner had installed an LED ring around the BMW emblem on the back of the car. During the installation, they did not run the wires correctly, and it was pinched inside where the emblem lights connected. However, after doing some research, someone told me that this was a "Pretty common issue, the latch sucks. [his] was doing what [mine] did and [his] mechanic fixed it once by "giggling" some connections. That bought [him] a year or so until a couple of months ago the mechanical latch failed. It cost me about $200 to get a new one installed which has fixed all the electrical problems as well. [He didn't] think the original ever worked perfectly."

So that might actually help someone else with the same issue. Thank you for your help.

[puddinboo]

k cool thanks for explaining

[racingbmwm3]

Originally Posted by macmac80210

Thank you for the extensive reply. I opened it up, and one of the wires was severed. I did a little fix, and everything is back and working great. Thank you so much for the help.

You're welcome. Glad it was something fairly simple, and cheap!