582 over charging

I have a grey head 582 which seems to be overcharging on the electrical system.

My volts gauge with engine not running will read 12.8 volts. Once engine is started the volt read 16. I have verified the volts with a multi meter and confirmed the gauge is reading correctly.

I am assuming the problem is associated with the regulator/rectifier. It has the rectangular alloy block with cooling fins on the top type regulator on it, with 1 black wire and 3 yellow wires. The black wire connects to the positive terminal on battery, 2 of the yellow wires join into a wiring harness and the 3rd yellow wire is not utilized.

Does the regulator need replacing or is there an option to swap out one of the yellow wires for the unused one and get another life out of the regulator.

If it needs replacing is there a cheaper option than the $250 rotax part