Aloha Jack Jones ,
"Neutral Safety Switch" Lacking any actionable ideas as to "trouble shooting" the NSS from various searches, both here and on other forums, I did the following. Hope this will assist you if the need arises. The NSS provides 3 functions,,,start in P...break light on...and start in N. Any thing else and the unit is out of adjustment or is kaaput.
Looking at the NSS from the front of the w113 as it is mounted on the firewall, the control lever is on the left, actuated by a bowden cable from the autmatic trans. On the right side are 6 poles (on mine) revealed when the plug is removed. I'll label the poles as follows;
a b c
d e f
Continuity is key here...is the unit good?...correct position of lever to action desired
#1 with the lever disconnected from the bowden cable, place in the bottom out down position. Use ohm meter...my experience was poles c and f were the only points showing continuity...must be "P" start
#2 Move the lever up till a slight click can be felt or heard...chk continuity...my experience, only poles b and e showed continuity...must be back up lights
I plugged the harness back in and bang I had backup lights... Any way, I put my car in reverse, adjusted the cable so that the cup connector lined up with the ball on the lever held in this position, got back into the car for the real test, start in P, NO start in R and start in N.
All is well until something else pops up...hope this is of some help...thanks again to you, 66andblue and bonnyboy
later...frank