Hi Scottie,
Dont know if you found this... but heres a sparx toubleshooting 'pic'.
http://www.tri-corengland.com/acatalog/Ignition_fault_finding.htmlThe coil resistance(s) needs to be above 2.4 ohms; 3 to 7 ohms for single or twin coils seems to be the 'target'. The unit cant carry more than 5 amps according to the above.
In terms of watts, resistance relationships, heres a quick couple of formulas:
Volts = Current (I)*Resistance(R)
Power (watts or VA) = I*V = I
2*R = V
2/R
This works in a resistive circuit, and doesnt take into account the 'magnetics' from the alternator and the coils. If I recall correctly, you have a 120 w alternator (I think), which should yield about 9.4A @12.8 V.... If the sparx requires no more than 5 A; and the headlight is ~ 50W, requiring about 4A that totals very close to 9A. Additionally, any 'loops of wires' or poor electrical connections can add resistance or magnetic coupling, which can further tax the electrical system.
If i was in your place i'd: 1) Make sure electrical connections are clean and tight; 2) remove any loops or coils of extra wire involved with the Sparx; 3) check coil resistance (wired in series?) is greater than 2.4 ohms; 4) change out regulator.
Just my thinking anyway and not sure if it helps.