schematic proof read

Then you have to invert one of them - probably with a relay - and probably the truck (especially if the flasher is load dependent).

no, the flashers aren't load dependent... that just gets back to the worry about the durability of the relay with that many cycles... how would i use a transistor to invert it?no signature needed

Why worry about the relay cycles - isn't a life if 0.1 to 1 million enough? Flasher cans use relays though some are thermo-electric types (for the timing). Only modern LED flashers are likely to use transistors etc. But rethinking this, since you have 2 power sources - namely the strobe & the brake - both will have to be +ve switched and joined through diodes to LED +ve. Note that if the strobes do use 2 +ve feeds & 2 gnd feeds for their flashing, that's a different solution - eg, the brake circuit causes all LEDs to connect wired to +12V & GND. I lost track of what devices you were going to use, and their specs.

At this point, I've now emailed the manufacture asking if it is switched positive or switched ground, hopefully all will be simple and only need a few diodes... We shall see though! Also, I've replaced the thermo-electric flasher with an led type, so monkeying around with that won't change anything... Though I would personally be a little weary of cutting the stock wiring up to put the relay in there... I don't trust myself enough to do that...no signature needed

If you're talking about the strobe module, that's both... But you shouldn't have to cut stock wiring, Things like this are usually add-ons.