Hello all, I’d like to thank you for your replies and give you an update on the fault. The machine owner had let the battery go completely flat and attempted to charge it but connected the charger backwards. The battery took a charge but now had reverse polarity, if that’s possible. I confirmed this with a multimeter across battery terminals. This I believe damaged the regulator diodes which I confirmed following regulator resistance tests in service manual. Also found charging circuit 20 amp fuse Melted to the fuse block. I bypassed the fuse block with an in-line 20 amp fuse which solved the charging issue.