I have 1991 Cruisers with Volvo Penta 570DP (570A). My ignition coil seemed to be working fine, but I recently noticed there was a crack in the top. So I figured I better replace it before it leaves me stranded. In doing this I learned there is supposed to be a "ballast resistor" inline to the positive terminal on the coil to limit the voltage to 9-10 volts while engine is running. I installed the new coil (Sierra - volvo part no longer available) and found that I have 13 volts at the positive terminal. I cannot find the ballast resistor anywhere. I'm only the second owner of this boat and I thought it was fairly unmolested, but it would seem that for some reason somebody removed the ballast resistor. The ballast resistor is also no longer available from Volvo.

I'm looking for any wiring diagrams or info on the ballast resistor so that I can hopefully install a new one to bring the voltage down. Apparently the higher voltage has not been an issue for the 6-7 years I have owned the boat. Other than possibly overheating the coil causing the "plastic" on top to crack. But now that I know it's not right, I would like to fix it.

Any help would be greatly appreciated. Thank you!