like stated earlier, first make sure installation is correct, gap and alignment. Next make sure the connections are clean and secure. Some of the obvious were stated earlier. The use of an A/C meter does tell if there is output, but not if there is proper phasing and waveform.
An scope is a better tool, a crank trigger is a simple switch and switches from hi to low or low to hi with each passing of a trigger.
There are usually 4 triggers on a wheel and will trigger at a rate of 4 times the engine RPM. The switch waveform should be clean and noise free.
Another possibility is noise generated by an alternator or RF from the ignition system. Make sure your trigger extension wire is a shielded wire with a properly grounded drain wire.
Most of us don't have a scope available so check the connections, phasing and gap and you will probably find it if it's the crank trigger.
Triggers are very reliable so check the obvious. An A/C voltmeter will give you an indication of average voltage to the switch.