here are the first things i would check (or have a mechanic checked). number one is to make sure the msd box is fed around 12 volts on the big red wire (all wires mentionned are those coming out of the msd box). check with a test ligth or voltmeter. next make sure the box is grounded on the big black wire. also the small red wire should receive voltage when you start the engine or if the key is in the `run` position. if everything checks fine, with the key in the run position, touch a good ground with the white wire , it should spark each time this wire touches ground. my best bet is you dont receive voltage on the small red wire, which would mean a bad ballast resistor ,if you are using one. as has been said you could jump both sides of the ballast resistor and see if it works.