Recurring start up failure on Volvo MD2040

[JCC]

Hello,
Had two of these in other boats- never a problem.
Now have 2000 MD2040 in a one-off Stewart 37 race keelboat.
Recommissioning spring 2021 after little use in 2020, one time in ten, my panel lights will not light, but the engine will start, although sometimes the starter pushbutton will not fire the starter.
Next it'll behave perfectly- but in preparing for the next few starts all four warning lights flash.
If I leave the ignition (pushbutton- no key) on - engine static, sometimes Ill get a twitch on the tacho, it might even do two or three and go all the way to 100%-
If I leave the ignition on- engine static, the oil warning light will pulse slightly dimming briefly.

New alternator, new diode on panel, clean fuse block, new on/off pushbutton.
And when anybody's looking- behaves perfectly!

Did have an accidental very brief OFF on the battery selector, caused original filament warning light/control block to totally melt down- almost combust (smelly). But tacho still ran.
Replace ALT anyway.

Could it be poor AGM battery health?
Help- next step- psychotherapy.
JCC

 

[slipknot]

This may not help...... but on my 2030 I had a very intermittent ignition light/starting issue. It turned out to be a break in the big earth tag connection under the engine. Cable had broken in the heat shrink allowing intermittent connection. Good luck finding your fault.

 

[Moodysailor]

You might have a poor connection in the loom to panel, or loom to engine plug, the AMP plugs they used at that time were OK, but susceptible to contacts wearing, especially if the lockrings have failed.

 

[JCC]

Thankyou Moodysailor and Slipknot. I’ve been through most engine terminal and loom connector scenarios- I’ve replaced diode on panel, on/off push button, switched a new relay in to the two slots in the black box- had the engine Earth connection replaced (dropped out in my hand), still very moody! Not happy about the ‘bridge’ on the earth for the battery condition monitor- will clean or remove, and will next try a direct engine to panel positive and negative feed, then direct from battery. Also thought I’d try a single, new deep cycle lead acid battery- I believe this sporadic charge variation can be AGM’s reaching end of life.
Amy ideas about the 33ohm resistor- where is it?
jc