On an older car, the ignition wires may not survive being disturbed when the car is tuned up. Start the car in a dark garage with the hood up (safely, with the e-brake on and garage door open, of course) and look for sparks and corona. This happened to me - so I replaced the honest-to-goodness original 18-year old wires!

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86 560SL
With homebrew first gear start!
85 380SL
Daily Driver Project

http://juliepalooza.8m.com/sl/mercedes.htm