2000 rodeo electrical? problems

I have a 2000 rodeo , 3.2 w/ auto trans. I have several electrical problems (I think they are electrical)
1) check engine light comes on for no apparent reason (usually resets with the removal/replacement of the negative battery terminal.)
2) flashing low fuel light with more than 1/2 tank (used to be on occasion, but is now constant)
3) automatic transmission position (dash light indicator) does not match selection on stick (sometimes when I shift from reverse to drive on start up, the display stays in the reverse position. This usually goes away if I turn the power off and then restart)
4) Intermittent wiper fuction has failed, (it begins to sweep, and stops about 1/4 of the way through the cycle, AND wipers stop in position when turned off. (they do not return to a home postion)

What is going on?
Computer? Weak Battery? Bad Alternator?

I have installed an aftermarket audio system, but had no problems for 2 years.

1. could be this:
http://www.geocities.com/endre_rl/isuzufaq.htm#faq1

2. its this:
http://www.geocities.com/endre_rl/isuzufaq.htm#faq2

3.its this:
http://www.geocities.com/endre_rl/isuzufaq.htm#faq59

4. I have the same problem too:

http://www.automotiveforums.com/vbulletin/showthread.php?t=243753

#1 check engine light on have it checked you will have P0463 fuel levell sensor circuit high input if you are the original owner and have less than 120,000 miles on it then Isuzu will pay for a new fuel pump to be installed. If not then you will need to purchase a fuel sending unit appx. $43

#2 see #1

#3 follow amigos advice

#4 alarm/relay module needs to be replaced