My son's 96 grand cherokee kill's the battery when engine is shutoff and also when running the volt meter will be o.k. for a bit and then nose dive to 0 volts. had alt. checked o.k.. seemed to start acting up when it rains??

define power.
1: can't hear buzz?
2: fuel pressure at the fuel rail is zero PSI cranked.
3: my volt meter tells me the pump has 0vdc across the pump pins cranked?

I cant guess any of this and is 100 %^ Germain.

what engine option????????????????????????????
that dash meter is a volt meter.
so when that meter varies
connect any hand meter, DMM (volts) to the battery lugs
do both meters vary,?,, yes, BINGO its not fibbing to you, the
voltage is out of control. per below:
but key on volts is 12.6v
and running does vary from 13.3 to 15v, this is NORMAL
outside that range is AB-NORMAL.(running)

post actual accurate voltages. and we cant find true cause.
is engine RPM always above 800 rpm
is the alternator fan belt at spec, tension?

if engine RPM drops , way low the ALT drops.
if the belt slips ,same deal.
My 4.0L uses a serpentine belt that must be set real tight.
100lbs. in fact. i have a spec tool to do that. (guessing dont work)
tell engine on 02 GC and we can look it up.

judging logically by what you mentioned I would check the oil pump first.

it may have deffective diode on the charging system(the alternator). 14 volts is an over charge in a battery. ampere reading must be on what the battery designed.

battery could be at fault or there is a draw in system that pulls down battery
have battery tested and leave it disconected for a few days then reconect to see if vehicle starts
if it does battery should be o.k. next is there any thing that stayes on (aftermarket stuff)
that may cause a draw on system if thats ok need to performed parasetic draw on system
hook up voltage meter between positive cable and meter
on 20 volt schale put red wire of meter to battery positive post black wire to red wire that was hook to battery voltaged should be minimal only to keep computers alive (clock - radio preset-etc etc)
if draw is high start removing fuses in system one at a time and check the voltage meter until it drops
you have now located the faulty cicuit that that fuse feeds start looking in those area
also feel starter selenoid and alternator at rear to see if they feel warm thet could be partly switch on
killing the battery over time
good luck

ok when the pcm detects something wrong whit the charging system the pcm show you in your board CHECK GAGES if this is not on, dont worry about

Also check brake switch adjustment, it is the interrupter.

Check the alternator output, with engine running and a volt meter check voltage at battery that be alternator out put voltage for the alternator, should not have less then 13.5 volt's with engine running, if less bad alternator, replace it

check all grounds first then start tracing looking for burned wires

get a circuit tester start it and check the battery to see what it is doing you should read 12.79 to 13.79 volts if it goes down to 9 or 10 volts and dies alternator!!! if it doesn't do the above I would look in to the coil pack!!