Decided to post to see what information others might be able to provide who know more about electrical issues than I . So , I have recently received a 2010 Toyota Highlander 3.5 V6 with the 2GR-FE engine that only had 72,000 miles on it , but water pump was leaking , and valve gaskets needed to be replaced . With that said I have discovered that any work on this vehicle requires taking a lot of other items off or removed to perform any task! Long story short I am taking my time and replacing a lot of items such as pulleys, belt, head gaskets and several other things. To do this I had to remove the alternator and move the A/C compressor to the side along with removing the fan and radiator itself. The first thing I did was disconnect the negative battery cable from the battery to avoid any kind of electrical issue however there were times I needed to access the interior of the car which I would then attach the negative cable to the battery post (negative) to then push unlock button on the key to access the inside of the car. I did this several times with no issue, but one day everything was dead so I thought the battery had drained since it is not getting recharged. I removed the battery and hooked up the charger and did a slow charge to the battery. When I hooked it back up , I got a lot (more than normal) sparking when placing the negative cable terminal to the negative post and there was no power anywhere to the car. Prior I could see the instrument panel light up and the doors would unlock when the button on key chain was pushed. I really am not in a position to take the car anywhere to have it looked at right now as I am still waiting on parts and bolts needed for several items being replaced so several parts have been removed from the car while I wait to receive these items (plus I broke a bolt off in the water pump housing so that is a work in progress.) I have looked at the fuses but did not see any blown fuses , but will do a second check just to make sure these old eyes did not miss the obvious. I have been told that it might be a ground issue , but not sure what I am looking for if that is the case and one other person said the starter or starter solenoid could have been affected which I am not sure how as I never tried to start the car or turn the ignition switch at any time . I am trying to view the cables and terminals which look old and tired but I am not seeing any corrosion on either . I know this is long but any thoughts would be appreciated as I am very limited in knowledge and ability when it comes to electrical issues. ( The truth is I started a simple task of just wanting to flush the radiator and replace the thermostat , then I saw the water pump leak and now 2 weeks later with half the engine pulled apart, sitting on jack stands waiting for bolts and other parts I am choosing to replace since I am already here basically...well I am the definition of Rabbit meet hole!!!! It's funny because it so true!