Land Cruiser J7-1HZ no current although battery is ok

Hello, my father has a Land Cruiser J7-1HZ from 1994, 4.2L diesel, and for a few days now the lighter doesn’t want to start, from one day to the other… Apparently the current from the battery does not arrive, although there are 2 batteries (converted to 24V), and they are fully charged. It doesn’t work at all, light, radio, light, etc. All cables and connectors “look ok”. (I had about the same problem on my car, diag; – cable from battery was broken.) My question; has one of you already had this kind of problem? or would a good mechanic have an idea of what that might be? thank me in advance and sorry for my writing mistakes.