1994 Mercedes R129 SL500 V12 swap: the no-crank fault returned
Kyle5647 reported no cranking and a fuel-pump problem on his V12-converted SL500. He later said relay replacement restored pump operation. Cranking also returned after ignition-switch work and reconnecting the neutral-safety switch, but stopped again. A final diagnosis and lasting no-crank repair were not confirmed.
A no-crank problem on a converted 1994 SL500
Kyle5647 identified his car as a 1994 SL500 and said it had a V12 conversion using what he described as stock computers and harnesses. He reported that the engine had cranked and the fuel pump had operated a week earlier, but neither worked after the car sat. A neutral-safety switch that showed a fault had been replaced, yet the engine still would not crank. He initially said the fuel-pump relay tested as working and that the throttle body clicked with the car switched on. The exact engine and conversion wiring were not established.
Parts and voltage checks did not establish the cause
He described battery checks, a separate starter test, K38 relay replacement and further electrical checks. In a later update, he said replacing the relay in the trunk restored fuel-pump operation, although the pump sounded rough. Turning the key still did not crank the engine. He then worked on the ignition switch and neutral-safety switch circuit. The discussion contains multiple suggested checks, but none established the final cause of the recurring fault.
An apparent breakthrough, followed by recurrence
After replacing the ignition switch, Kyle5647 realized the neutral-safety switch was still disconnected from an earlier test. He reconnected it and reported that cranking returned, leading him to credit the ignition switch. His later update said the car had stopped cranking again. That recurrence changes the conclusion: the thread does not establish a lasting ignition-switch fix or a final root cause.