@ShaneP is correct. Ohm's law. If you double the resistance with the same amperage, the voltage must be halved. No way around it. Think back to your simple circuit of a power supply/battery, fuse, switch, and globe (load) that they teach (I did it again just this week, and did it before during my Cert 2). If you add another globe in series, they both run dimmer. Exactly the same thing. Double the resistance, the same amperage, half the voltage. Parallel circuits multiply the amperage and half the resistance. Was discussing this problem with my teacher at TAFE today... the gist of it was to wire them up in parallel and see what happens, or 'suck it and see' - my main concerns are blowing the transistors in the TCI, blowing fuses or melting the wiring. With all that said, my ZXR has been happily running along since I did the original installation and it has been running fine, so clearly there is enough juice for a decent spark. Wiring them in parallel will require resistors.