My 1990 isuzu troopers fuel pump is constantly running and making the battery go dead even though the key and engine is off. What can be the problem?

which engine, ill toss coin, land on v6
check fuses first.
wont crank? that grrrrr grrrrr grrrrr sound
jumper cable start it yet, why not?
or put in a known good charged car battery?
or using any battery charger charge yours?
or buy a new battery, (if rich)

if it cranks and wont start?
check spark x6 (scan it yet?)
if sparks ok try test fuel!
if test fuel fails 100% see bad belt below.

EVER REPLACE THE CAM BELT?
if not and over 60k on the last one
the belt is doomed, living on borrowed time.
got the V6?

If your Trooper "cranks" but doesn't start or runs for a few seconds and stalls out, your fuel pump has gone bad. They are notorious for this. If you replace your fuel pump, replace your fuel filter. More information is needed though.

Is it diesel or petrol

i had similar problems with my 1989 as well as the wife's 1990....my problem was freyed wires near gas tank as well as fuel pump relay...the wife's was relay as well.try to follow fuel pump and relay wires test along the way. hope this helps!!

Check the fuel pump relay and fuses it may not be getting power when you turn the key on.

start with pulling the fuel pump relay!!
this should kill the power to the pump and save your battery,
so well pulling the fuse but pull and test the relay,, it may have got to hot. if it checks good and clicks when you plug it back in!![key off]
then there is a short in the ignition to relay circuit

It is located inside your gas tank

Well, could be many things, but first and easiest, check the dist. cap and rotor, and all the plug connections. Any moisture will freeze and short out the ignition system. Also change the fuel filter. If you get the slightest moisture in the fuel it will lock up the filter when the water freezes. Could be a relay, probably "engine relay" that sticks when it gets too cold.

Some starting points I hope.

On all Trooper II models the fuel pump is located in the fuel tank, fuel tank must be removed to access.

Look under the plastic intake tube for a hole