By "switched 12v", are we to assume you're looking for hot in run AND start? Or just in run?
The ignition switch (which I assume you're still using) does not have an output that is hot in both run and start, they are two separate circuits- "IGN1" (run) and "IGN2" (start). When adding aftermarket ignitions (or in your case, a relay) these two feeds are generally connected together to supply a "constant" switched 12v source.
But since you have already sliced and diced your harness, you may have eliminated one or the other already- you'll have to go back and reinstall one or the other if necessary. If you have eliminated the ignition switch (running switch functions through a toggle panel), you'll have to figure that out on your own dependent on how you rewired the thing.
NOTE: IGN2 is hot in start- but it is NOT the starter circuit and is not run off the starter relay. Running your ignition off of the relay could cause backfeed issues that do not allow the starter to disengage, and can introduce other wonky quirks into the system.
And that really looks like an MSD box, not a Mallory.