FWIW, neither the 380 nor the 560 have any sort of relay in the start path. The 123's had an AC relay that would fail and produce the same symptoms, but on a 107, I believe that the only thing between the ignition switch and the solenoid is the transmission switch to make sure you are in Park or Neutral.

Since the 500 block is aluminum, a ground strap from a starter bolt to the frame is a good idea. The 126's and many other models have them.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe