Whelan Strobe Troubleshooting...

Does anyone know how to go about trouble shooting a Whelan strobe
light? It is on a Piper Cherokee and is the "beacon" of the airplane.
I had an extra bulb I don't know the status of and swapped it out, but
still didn't get any emission. I'm thinking that its probably the
unit, but I don't know how to prove it since it isn't a continuous
power light.

There are 3 wires on the clip. A white, black, and red. I think the
red is what gives the pulse to the strobe and the black is ground of
course. The white has a sticker on it that says 13V so my assumption
is that that should be continuous power. Is my assumption correct?
If it is I know its the unit because I don't get any reading on the
meter when I connect to the black and white wires.

Is there somewhere I can look to get additional information? Any help
would be appreciated. At 350 dollars I'd like to be sure I'm
replacing the correct part and don't just need the 75 dollar bulb.

TIA for any responses.
z