[W126 Coupe] Seat belt retractor door pin switch test

[Dick Spellman]

Mi Mike:

The door pin switches on my coupe are the same part # which is: 001 545 
87 14.  Please do the following before replacing the switch.  Turn the 
ignition key to on with door open. Then depress the upper button to see 
if it cancels the buzzer and the courtesy lamp.  If it does you know 
this switch is okay and has nothing to do with your seatbelt extension 
arm circuit.  You can release it and move on to the lower pin switch.  
Yours could be reversed this is simply a step to identify which one is 
for the arm extention circuit.

Now depress the lower pin switch and hold (as if you were closing the 
coupe door) the arm should start to extend.  At the point where you 
release this switch the arm should start to retract because the circuit 
determines the door is open.  This is the correct operation for the 
seatbelt extension arm.  What you described would mean that as soon as 
you open the door the pin switch the arm comes forward.  This is the 
reverse of what you should see.

Once you have confirmed which pin switch (upper or lower) operates the 
seatbelt arm, turn off the ignition and remove the switch. (Depress the 
outer clips with your fingers (top and bottom) and pull.  The wiring 
will be stiff so take your time getting the switch out far enough to 
disconnect the two spade lugs on the back.  Tape the two leads to the 
door frame so they don't go back in the hole.  If either spade lug is 
missing the plastic insulator, tape it to prevent a short to chassis 
ground then tape it to the door frame.

Last item, just take a volt/ohm meter set to any scale for OHMS and 
connect to the two spade plugs on the switch.  The switch with the 
plunger out is said to be Normally Closed.  Meaning it is making a 
complete circuit when the door is open.  So you should see your analog 
needle go to 0 ohms or so and stay there.  If it's a digital meter will 
read close to 0 as well.  When you depress the plunger the circuit 
should go to OPEN where the needle goes to resting position (typically 
the left) and if digital the readout will be O.L.

If the switch does not behave as described, go to local MB stealership 
and by another using the above part #.  They are something like $2-3.  
Been a while since I bought one.  Install and test again.

Dick