Diagram for 1990 Chevy Van 10 4.3 vortec Alternator diagram

Question edited for clarity.

Does it look like this?

https://images.app.goo.gl/1vY1ZuWhdxuZi6xA8

More here

https://www.google.com/search?q=1988+P20+step+van+6.2+serpentine+belt+diagram

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Donald, You did not state the model, so I posted the link for the models I found for chevy van fuse box. Check the attached links,instruction and guides, Good luck
"I hope this helped you out, if so let me know by pressing the helpful button. Check out some of my other posts if you need more tips and info."
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first is alternator/ water pump/ crank... second is power steering and smog if equipted.. last is ac compressor..

i have a new site for auto diagrams (AA1car.com) auto diagnostic &repair help,give it a try ,hope it helps ,good luck.

First of all you need to confirm the case of the alternator before it is replaced and I hope that the output voltage from the alternator was checked. However if voltage is present the fault can be with the rectifier/regulator.
Now the alternator is clamped on to the enigne side with the pulley threading in line with the main belt.
You need to have box spanners to remove the side clamps holding the alternator so as to loosen the unit . While refitting the tension of the belt is most important as you need help to keep it tight while the bolts are fastened .
If a new alternator is not purchased then it will be best to have it done at the dealership as the cost of part will include the replacement.So check for estimate before you remove the unit.

If nobody here provides it for you (I don't have your van's manual), then visit the chevy dealership and ask a not-too-busy shop foreman or a parts dept. person for a little assistance. A quick look in a repair manual for your van may also have it. It must have got scraped off or disappeared from under your hood, on a little sticker?

DRIVE BELT DECAL SHOULD BE UNDER THE HOOD.OR YOU CAN GO TO DEALERSHIP GET ONE AUTO ZONE OR ADVANCE AUTO PARTS CAN GET YOU ONE.OR YOU CAN BUY A HAYNES REPAIR MANUAL IT HAS BELT DIAGRAM.

My sincere apologies for the delayed response.
I am personally going back to answer your unanswered questions.

I do not know if you still need this information, but I am going ahead and answering it anyway. You may want to Print the Diagrams for future use.

I am assuming this "van" is a Chevy Venture?
CLICK on the following LINK. It has the Belt Diagrams you will need.
If you would: Before Clicking: Let me know if this helped you, or if you have any additional information or questions. Feel Free to contact me at FixYa.com!
Again my apologies...
http://www.2carpros.com/car_repair_information/year/2000/make/chevrolet/model/venture/2000_chevrolet_venture_drive_belt_routing_diagram.htm

Before removing belt, look for a belt routing diagram somewhere under the hood. If you don't see one, sketch a diagram for reference or you may have a struggle getting it back on correctly.

Most gm products with serpentine belt have a springloaded tensioner.
Using either an open-end wrench or a square drive tool (breaker bar, ratchet, etc.), you can relieve tension on the belt, allowing it to slip off of one of the pulleys. This will give you the slack you need. Be careful when remounting the belt that you get the belt properly loaded onto each pulley. If you're off a groove and start the engine, you may seriously damage the belt. While you have it off, inspect for cracks. In my experience, those don't get replaced on schedule. If there is significant cracking on the grooved side, you may want to replace it.

Hope this is what you needed.