Weird “Idiot” Light Behavior

[Nordski]

I have a Volvo TAMD61 on 1987 CHB42.

When I have the battery switch set to charge the house batteries off the main engine the overheat and voltage idiots come on. The two gauges do not reflect any abnormality. This was not the case originally.

Also once this began those two lights remain dimly on after starting the engine for about 30 seconds.

Anybody have any ideas what is causing this?

 

[RT Firefly]

Greetings,
Mr. N. Welcome aboard if I've missed you. The FIRST thing I do with any electrical anomalies is check all wiring and connections. Don't forget your grounds.