First of all, there are typically two ways of making sure your construction is safe:

• Use an off-the-shelf approved product and install it exactly in the approved way.
• Design your own solution and do a real load calculation to prove that all the loads and possible failure modes are accounted for.

Your question sounds like you're trying to pick the latter option, but handwave away the expensive part of it. Perhaps you can get away with it if the design is indeed sound, but without analyzing the loads, you can never be sure. Various authorities take a dim view of people who say "actually dunno, but my gut feeling is that this will hold".

Regarding the loads, you likely realized that the primary load (compression of the posts) is not really the reason for these connectors. If it were, you wouldn't need any plates at all, you could just place the beam on top of the post and that would do just fine.

Instead, the post caps are there to carry the horizontal loads in both axes (along the beam and perpendicular to it). That's why the post cap looks the way it does. There will always be such loads, because of:

• Posts not being exactly vertical, not having exactly the same height, sinking by different amounts over time, etc.
• Beams not being exactly horizontal (including some sagging).
• Non-uniform loading of the deck, dynamic loads (people, wind).

These forces are going to be significant. If the post ends up being inclined 1% away from the vertical (and that's just a tiny bit), 1% of the weight of the deck is going to act on the post sideways, trying to topple it. All the other forces mentioned above just add to that.

Your two plates could perhaps easily handle the loads perpendicular to them. However, the other direction is more tricky. You would likely have just the clamping force multiplied by the friction coefficient between smooth steel and wood (not a lot). With a lot of luck, the shear loads on the bolts could also help, but good luck drilling those four holes exactly so that you hit all four holes on either side. (More likely, the bolts will be loose in their holes and thus not active.)

Also, relying on the clamping force means that you'll have to:

• Ensure that the beam is exactly as wide as the post, so the plates rest flat against both the post and the beam.
• Tighten the nuts sufficiently to apply the necessary clamping force.
• Periodically check and re-tighten, because the weather and all the wiggling from the dynamic loads is going to make the wood give way over time.

So to summarize, your design surely can work if designed properly, but there's a whole lot of factors that need to be taken into account.

It sounds like you're suggesting drilling the beam clear through from top to bottom, or notching the side of one of the outer 2x8s from top to bottom. Neither of these are allowed under modern building codes and they significantly compromise the capacity of the beam. It's like subtracting one of those 2x8s from the beam.

With that said, I previously owned a house where water supply pipes had been inserted top-to-bottom through a structural beam, and the house had not fallen down 30+ years after it'd been done. Thank goodness for safety factors!

Instead, build a chase

If I were you, I would build a small chase to bring the wiring from the joist cavity into the wall.