The design of the stock power pack is quite good. They are about as rugged and simple as can be. A dead short on the HV output, it just shuts down and ceases to oscillate.
I learned this early on when I bought my 66 Charger. At that time, knew nothing about EL lighting. I had to quickly learn as my car had no working EL when I bought it. As I was
learning how everything worked, having a good electronics background helped. Before I tore into everything, I had bought one of those E bay solid state power pack's with the bad assumption
my power pack was defective. Well that was a waste of $$ as first time I hooked up the solid state E bay unit up to a gauge with shorted needle, it failed and was useless. So, pulled the power
pack from the car and Hooked up the stock power pack on the bench with no load to test, and it worked perfectly, so I was able to continue testing my gauge cluster. Turned out to be two shorted
gauge needles that I eventually figured out how to fix. Best advice is stay with a stock power pack. There are 3 resistors, 1 transistor and 1 capacitor. Probably $ 10 worth of passive parts.
With EL lighting, check the power pack first ! Test it with the white wire NOT connected to anything, chances are it's not the problem. If you hearing is good enough, you can hear it making a
high pitched whine, that's a good sign it's working.