I have no specific information as to the 288, so my info should be treaded as generic.
Typically the red shorepower light comes on if the "neutral" side of the boat is wired to the "hot" side of the shorepower pedestal - which is reverse polarity.
Boats are a bit different than houses. In a typical home, the neutral and ground side are connected together.
In a boat, they are separate.
This is actually done for safety.
This is one reason that you have a breaker on both the "hot" and "neutral" leads on the main breaker panel.
However, the neutral AND ground connections are tied together on the shorepower pedestal, so when you connect the boat to shorepower, the neutral and ground connections "at the boat" then become tied together by proxy.
If this were not done this way, and the neutral and ground connections were tied together at the boat, then a condition could exist whereby a direct short could occur should the shorepower pedestal be mis-wired, which is the other reason for the main breaker on the neutral side as well as the hot side.
Since the galvanic isolator is on the ground side of the boat, I cannot see how a bad isolator would make the red light come on; unless the red light is dual purpose; i.e. shows a mis-wired condition AND a bad isolator.
One added complexity you have is a genset. This might result in having an isolation transformer or other equipment on board.
The ABYC has mandated somewhere in 2000 or 2001 or so, that all new galvanic isolators have a circuit to tell when they are bad, so maybe your red light indicates this? Otherwise, I am not sure a lot of manufacturers have adopted this ABYC requirement, since it is optional.
So the first question, has anyone added any wiring to the boat; dealer or owner? If so, make sure they have not connected the ground and neutral wires together anywhere.
If you think it is the isolator you can test it; but you need an ohmmeter that puts out more than 1.5VDC in the ohms scale. The way ohmmeters work is that they inject a voltage to the circuit, and then make a calculation from the result. Often the voltage used is from a 1.5VDC 'AA' cell, which actually over time will be less voltage.
By the way Cap'n; some isolators have a capacitor and some do not. I do believe that our V268s have a capacitor, so your test procedure would work for those.
You also need to absolutely be sure that your shorepower pedestal is wired correctly. This will rule out for sure whether or not you have a problem.
You can make an adapter (or buy one) for both the pedestal and boat ends of the shorepower cable.
If you want to make one, use this diagram below:
WARNING: I TAKE NO RESPONSIBILITY FOR ANY RESULT IF YOU DECIDE TO MAKE YOUR OWN.
If you are not sure what to do, you can buy these:
Marinco 81A:
Marinco 83A:
Of course, these are expensive. When I made mine, I went to Home Depot and bought the parts for about half the cost. The 30 amp connectors are NEMA L5-30P and L5-30R; if I recall, P for Plug, and R for receptacle.
I use the one with the male 15A connector to hook the boat up each spring when I do the spring commissioning so that I can charge the batteries from a 15A outlet.
I use the other one so that I can plug accessories in at the shorepower pedestal (such as my George Foreman electric grille) while at the dock. It is also useful for "testing" a shorepower pedestal at a transient dock when used in conjunction with one of those inexpensive circuit polarity testers:
Of course, this little tester does nothing the red light in your electrical panel doesn't. Except when you test the pedestal with it, it rules out everything but the pedestal.
If you use shorepower, these items should be in your toolbox.
So to close, in my view, you need to make sure where the problem isn't, so buy or make an adapter cable, then test the polarity of your shorepower pedestal. Only then will you know if the problem is with your boat or with the pedestal itself.