Arneson drive

You mean that the Arneson drives are going down rather than up when you trim up and viceversa, I suppose?
If by operating the trim you would reverse the propeller rotation, that would be VERY worrying!
Anyway, if my understanding above is correct, it does sound like a wiring problem, no matter how careful you were in your job...

Well, if you neither touched the pump relais nor the solenoids, I can't imagine how they could be the culprit, assuming that everything worked well before the gauges wiring replacement...

If you don't mind me asking, what engines have you got on your P52?
I believe they were built with either V8/800 or V10/1050.
Just curious!

I would think that with a defective solenoid you should be able to trim the drive only up or only down, but if it works well both ways and the problem is just the reversed control, there shouldn't be anything wrong with the solenoids. Do you have any reason to suspect that?

All that aside, I would suggest you to keep the hull and propellers religiously clean.
Your D2848LE403 are solid engines, which I know fairly well because I've got them right under the settee of my boat from where I'm writing!
But they are a bit stretched to their limit by the Arneson drives of the P52.
So, if and when due to dirty hull/props you should struggle to bring the boat up on the plane, don't insist too much, and get her cleaned ASAP instead.
Keeping the engines at WOT for some time while they are unable to increase the RPM/speed is the best recipe for overloading them, with EGT going ballistic, potentially to the point of making some serious damage.
Sorry if this sounds a bit scaremongering, but I'm aware of a chap on this side of the Pond who experienced exactly that, with your very same boat...

I would call the Arneson service guy to be sure before touching any wires. However, as long as the Arnesons move as requested and you can verify it realtime, I would probably cruise as-is. Also, as this seems to be discussed, I applied Prop Speed in the summer to see what happens, and it appears to be working well. The props don't require cleaning anymore after the boat sat for a couple of months and the performance appears to be the same. Replacing an EGT sender when obvious discrepancies started arising also proved good this summer. More painful was the cleaning of the main heat exchangers.

No EGT probe+gauge on the OP engines.
Unless retrofitted, which is a possibility I toyed with also for my boat, because it's sufficient to remove a plug just downstream of each turbo, fit probes in them, and connect them to some gauge at the helm. It's still in my "nice to have but not really necessary" list...
But in my boat these engines are driving plain vanilla shafts, and even just by the seat of the pants it's pretty obvious that they are never stressed, through the whole RPM range - also whenever her bottom is a bit dirty.
In the OP boots, considering the type of boat and the surface drives, I'd probably move EGT monitoring from nice to have to "do ASAP" ranking...

EGT, definitely one of the most important monitoring tools in my Arneson propelled Mangusta. Watch it all the time. Also (and I only recently found out) the high oil temp seems to be of major concern on MTUs.