Alternator removal on 1997 Isuzu Trooper

step one remove battery neg lug .
the above video (of book?) is wrong.
the belt tension-ing step was skipped.

remove belt steps remove alt. wiring. remove alternator (bolts) it falls free. replace it , reverse steps above belt back tension belt. battery cable back. test run. charge/BAT lamp off?
see wrench below, turn it CW.
this releases the spring tension and belt comes off
to put back, do same and put on belt and release wrench.

3.5L only. USA only.

I would start with having your alternator tested (must be removed and taken in to an auto parts store). If the alternator tests fine, make sure all of your ground wires are connected.

You say the alternator tested good, on the car or off ?
There are two fuses from the alternator to the key switch, a 7.5 amp and a 15 amp. There is also an 80 amp fuse from the alternator to the battery.
I would check these fuses and the connections at the alternator, plus the ground between the engine and the frame.

Alternator REMOVAL 3.2L Engine

1. Before servicing the vehicle, refer to the precautions in the beginning of this section.
2. Remove or disconnect the following:
   • Negative battery cable
   • Front splash shield
   • Alternator drive belt
   • Adjuster
   • Top alternator bolt
   • Alternator wiring connectors
   • Alternator

3.5L Engine

1. Before servicing the vehicle, refer to the precautions in the beginning of this section.
2. Remove or disconnect the following:
• Negative battery cable
• Accessory drive belt
• Alternator wiring connectors
• Alternator

INSTALLATION 3.2L Engine

1. Install or connect the following:
   • Alternator
   • Alternator wiring connectors
   • Top alternator bolt
   • Adjuster
   • Alternator drive belt. Tighten the alternator top bolt to 16 ft. lbs. (22 Nm) and the adjuster lock bolt to 17 ft. lbs. (24 Nm).
   • Front splash shield
   • Negative battery cable

3.5L Engine

1. Before servicing the vehicle, refer to the precautions in the beginning of this section.
2. Install or connect the following:
   • Alternator. Tighten the 10mm bolts to 30 ft. lbs. (41 Nm) and the 8mm bolts to 15 ft. lbs. (21 Nm).
   • Alternator wiring connectors
   • Accessory drive belt
   • Negative battery cable

Check the large cable on the alternator to make sure it has 12 volts on it with the engine not running,if it does not,then this is the problem,running a new one to the positive side of the battery to this terminal on the alternator will solve the problem.

This guide will help you : http://www.ehow.com/how_2210347_remove-vehicles-alternator.html

On the drivers side on the bottom front of the engine.

1. Remove battery terminals and secure them away from the battery posts using nylon wire ties.

1a. Fine some comfortable eye glasses (clear or yellow) and keep them on. There are plenty of opportunities to get debris in your eyes during this procedure.

2. Spray "PB Blaster" (loosens bolts) on two bolts that secures alternator.

3. Jack-up vehicle on side to access alternator. Use a jackstand to support.

4. Using a 10mm open-ended wrench, loosen the bolt that swings the alternator. Screwing the bolt "in" or toward the engine will allow play to increase in the alternator belt. Loosen the 12mm bolt slightly next to the 10mm bolt (approximately 1.5" toward engine).

5. Continue to loosen 10mm bolt until there is enough slack in the belt to remove the belt from the alternator pulley.

6. Remove belt. It may be possible to remove belt without removing fan faring. Maybe not. If not, you will need to remove plastic fairing. If you must remove fair, go below fan fairing and disassemble connectors that hold together pieces of fan fairing. Carefully remove.

7. Install alternator fan from above.

8. Check that alternator belt is on all tracks (from below with a flashlight), and slowly tighten.

9. Secure 10mm and 12mm bolts. Recheck tightness.

10. Reassemble battery connection and run vehicle at idle for about 5 minutes. Check belt for proper tension.

11. CAREFULLY check tension of belt. Or disassemble battery connections and re-check belt tension.

12. Reassemble fan fairing (if not already assembled), re-connect battery terminals, and have a nice day. :-)

You'll have to rock the alternator back and forth to get the bushing that the lower bolt goes through to slide back enough for the alternator to slide out.

You probably have this sorted by now as this post is a couple of weeks old but just in case you haven't, here goes.
Remove the front belt/s. Remove radiator cowl. Access the alternator bolts by removing right front wheel. Once diconnected, push the alt up past the radiator and into the hands of your assistant.
This method is for the 3.1td engine. If you have a V6 I have been told that the alt will come out through the wheel arch which will avoid removing the belts and cowl.
Also, don't forget to disconnect your battery/s.
Good luck.
Gary.