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I don’t know anything about the graham tester, but it may help to know how those two-spark wires coils work. Even so, there are a couple of schemes used. On most, such as the Evinrudes, the primary winding is conventional, and secondary winding terminates at each end and spark plug leads. In operation, electricity leaves one end of the coil, goes to a spark plug, jumps the gap, and then to “ground” (not really, just sayin’ for clarity). The electricity then travels through the cylinder block, to the other spark plug, jumps that plugs’ gap, and back to the other end of the coil, which completes the circuit. It’s important to realize here that the spark jumps across BOTH plugs’ gaps at the same time. Generally speaking, with most testers with only one spark gap, one of the spark plug wires is grounded for testing to provide that return back to the other end of the coil. I hope I’m making that understandable.
In any case, don’t worry, you won’t blow anything up by incorrect connections.
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