I have a 1978 Chris Craft Commander 410 with 454 crusader engines and paragon transmissions. I have noticed that the Trans oil pressure gauges on both engines drop to 0 when I put the boat in reverse but are normal in forward. I have checked the trans oil and it is fine.
I believe that this an instrumentation issue and not an issue with the trannys. I think this because it does this on BOTH engines and I have an alternator issue as well. The alternator/regulator is acting up. When motoring and the batteries are charged the alternator is putting out 16v on the panel. Any thought from the commander brain trust?
Are the gauges on your transmissions stock, or have they been added? I say this because most Paragons I'm familiar with don't have any gauges. Secondly, if the trannys are working this way, you most likely don't have a problem, because if something goes wrong like that and it IS a problem, something will stop working real fast. Therefore, what little I know about your trannys, I would think you are okay. Check the fluid and be sure you are not low, naturally.
Alternator still pumping with batteries charged? If batteries are charged and you are running the motors, you are taking something off the battery, and the alternator will want to charge back. If you get into an overcharge situation, I think your battery will soon start to feel warm. If you can get in there and put your hand on the battery, or use a pyrometer to check, you may find you are actually overcharging.
Have you put a separate stand alone voltmeter on the battery with the engine running to see if it really is charging 16 volts? Also if the electrical systems are hooked together between the 2 engines, such as when the battery selector switch is set on All, we have seen the voltage regulators confuse each other and not regulate properly. It is better, IMHO, to keep the electrical separate between the 2 engines.
This means the dash wiring/ gage panels should be separate as well. A previous owner can wire stuff in and inadvertantly join the 2 engines together electrically. This can cause 1 alternator to backfeed the other.
Try running 1 engine at a time and check voltages. I know this is not addressing the trans pressure deal, it sounds like a different problem, but with electrical who knows?