Hi there,
Do you have spark? Pull the wire off the center of the distributor and connect it to a spare spark plug, turn the engine over and look for spark... If no spark, you've isolated it to the ignition system. If you have spark, check for fuel! Perhaps the easiest way is to slightly loosen one of the fuel lines at the warm-up regulator, turn the ignition on for a few seconds and look to see if fuel ran out. If you have fuel and spark, do they occur at the correct time? (could be broken or jumped timing chain) If no fuel, check to see if the fuel pump is running. If not, check the fuse on the relay. Could be the fuel pump wore out, or the fuse is blown, or the relay is bad...

Good luck with it,
Richard Wooldridge

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Richard Wooldridge
'01 ML320
'82 300D 4.3L V6/T700R4 conversion
'82 380SL, '86 560SL engine/trans. installed
'79 450SL, digital servo update
'75 280C