89 legend problems

Hi,

I have some problems with my car that I know are common but I'm not able to find any answers.

First, the low oil light flashes even though the oil isn't low. I pull over to check the oil and then when I restart the car it's not flashing anymore.

Also, the alarm sounds when I unlock the drivers door. Is there a way I can just disconnect it?

And the fuel gauge is erratic. Sometimes it works and sometimes it don't.

What would really help me is an electrical diagram if anyone knows where I can get one.

Any help is appreciated. Thanks