About all you can do to test is check for power and ground, plus connectivity on all wires, especially the green one to the coil.

If everything checks out, then you need to try another unit.

I don't know about the older unit - I personally would spring for the correct used one. Try car-part. com.

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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