The new one seems to be working properly alltough I haven´t had the time for a longer drive yet. I´ve had the same configuration before in my other cars with no problems. I don´t think I´m going to put a fuse there because it would have to be strong enough not to blow when starting (~500A) so it would serve no purpose. I´m hoping this would also explain why my tachometer started to go crazy. I think the charger made too much current because there was a poor connection (or no connection) to the battery and the tachometer started flipping. Then, as I put more load to the charger (lights, fan, heater etc..) the tacho started working again, but after a while it started the flipping thing again.