On my mags
On my mags, the #1 is clearly marked on the cap where the wires come out. The harder part seems to finding the next cylinder to fire since that depends on whether it is a right of left mag.
I just used the pictures in the Lycoming manual to wire things up. I’ll make sure everything is right before first engine start, once I getbthe prop on, break the engine preservation, and start rotating the engine.