Your better off buying a tester off of ebay for 30bucks that
can test the plug and voltage (strength) of the spark.
Just clamps to the batter and one plug at a time.

If you just want to see it fire, the little light testers that go on
there for $5.00 will due ok. (small light encased in clear plastic
that goes in between the spark plug and the plug wire.

Building one out of leds??? Most likely more work that its
actually worth.

Tom

edolo wrote:
Have a couple of manual testers, but would like to build an LED
in-line unit to test spark on two, four, and six cylinder outboard
motors. Anyone have a design or know where such a unit can be obtain?
tks, alp