Re: Over Heating
well first off where is the coolant leaking from. this should be looked at, otherwise this means you have to keep toping up your system. not a lot of fun.
One common problem I know lots of people end up having (especially on second hand cars, if maintenance records are unknown) is the thermostat may be sticking, this could cause over heating problems. although there are many other possibilities such as temperature sensors not reading correctly, clogged passages, or even a bad radiator cap (the radiator cap may not be functioning properly letting out pressure that will allow the fluid to boil at higher lower levels, rather than higher).
As for the lights and grounding situation. follow the negative lead on your battery that should take you to a common ground on the car. there may also be other ground attached directly at that point. also this may be tricky but follow the lighting wiring, it might not just be bad grounding, there could be problems with a splice or connector where a vibration will enable a connection. this can also show you the exact ground lead for your lights if you follow them.
Wiring diagrams are a gift from above. see if you can find some for your specific vehicle and they will literally show everything about your lighting situation and that would be truly beneficial if it isn't a simply lighting problem.
I'm sorry I may not be of more assistance, but my knowledge is still very limited to cars and engines, and I try to offer the most information that I can. i hope it helps, if someone finds something that isn't correct feel free to correct me.