The older Volvos had an armored primary ignition circuit, supposedly to deter hotwiring the car. The positive terminal of the coil is in this armor covering on the bottom of the coil. Pertronix has an additional diode or something to work around this problem. I'm not familiar with Hotspark and how you could wire it in an older car with armored ignition. My 1800's coil failed and you won't believe what the price is even for a used one. You have to buy the coil and ignition switch together as a unit. I've seen them as high as $525.00. Ridiculous. What I did was to replace all that with a Bosch blue coil and a good quality generic ignition switch from a speed shop. It works perfectly. My tach even works. That might be another problem that Hotspark hasn't addressed. I hope you can find a workaround for the ignition you purchased.

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Roy Olson