merc 3.0 conventional ignition - no spark

I've got no spark from ignition coil. Boat was working last week. I gave the boat a tune up 3 weeks ago and replaced all ignition components - points, condenser, rotor, cap, wires, and plugs. I checked the voltage at the coil and only get 7.5 Volts. When I disconnect and read the purple wire from the + side of coil I get 12V. What started this was my temp gauge would barely get above 120 degrees. I tested the thermostat, temp sensor, and gauge, all of which seem to work correctly. Then I tested the tan signal wire at the sending unit and was only getting 9.5V. Figuring I should be seeing 12V at the sending unit I started looking for where I could be dropping part of the 12V and think I must have done something to screw up the ignition. I'm not terribly familiar with conventional ignition systems. Any ideas would be greatly appreciated

 

Run a jumper wire from the battery to the + on the coil. If that solves the problem, there is a bad or corroded connection somewhere.