Charge Light On at Night, Only

[deltasig]

Recently I had to motor during the night and I noticed the red Charge light on the Yanmar panel was on. No alarm sound just the light was on and I noticed it when it became really dark.
I checked the voltage at the starting battery and it was a solid 13.8 V. I figured the battery was charging and postponed further investigation for the next morning.

I double checked the R L and all other connections at both ends (alternator - instrument panel), verified the output of alternator and I could not see the red Charge light no matter how much I blocked the daylight. The starting sequence totally normal: turn ignition key -> all lights on and alarm sound, crank, engine starts, lights go out, rev to 800-900 to make sure after a few moments and all look fine. I figured something was not making good contact and as I moved the wires to check them reseated itself. So at night I try to see the result. Same starting sequence but the Charge light goes initially off for a few seconds and then starts getting red gradually and staying red.

The set up of the boat is as follows: House 2 x 200 Ah Gel wired in parallel as one bank, Starting 1 x 60 Ah Gel, Alternator stock Yanmar 55 A, Charger TrueCharge 40, 2 x Kyocera KD135GX panels regulated by Morningstar ProStar 30.
Alternator feeds to isolator to charge both House and Starting. ProStar 30 feeds solar current to the output of the TrueCharge 40 which feeds the House bank only. The Solar satisfy comfortably the day loads and keep the 2 x 200 Ah House fully charged even in the morning before dawn the House shows 12.7 V.

I suspected something may be happening with the fact that there's no current at night from the solar panels. I disconnected all the solar parts, started the engine and the Charge light did not come on.

Any thoughts?