Start problems

[Belgium R/T -68]

Wanted to start up the GTX after the succesful ride last week but the car was dead on the key. With the remote starter the engine cranks so I guess it's the trannycontact or the starterrelay itself. How/where do I messure the power to know where my problem sits? 

[Nacho-RT74]

check for power on yellow wire arriving to starter relay when trying to crank... if not power there, problem comes from ign switch or that wire related up to relay. If power there, the yes, probably sure is starter relay itself OR ground not coming from tranny NSS throught brown traced yellow wire. Check then for wire conditions, NSS conditions, NSS plug at tranny or tranny linkage out of adjustment.

If manual, then the same with wire coming from clutch pedal switch