My question is has anyone ever tried to fix the controller for 1999 suzuki grand vitara, mine has quit working? Also where can you buy one.

What do you mean by the controller? The main (ECU) computer / brain box, or something else?  

Not sure of proper name, but what ever turns the pump on and off to pressurize the differential with the 6 p.s.i. to lock in the drive axels.

Ah! OK. Here are some links to that info...   

http://www.suzuki-forums.com/1g-2001-2006-xl-7/35054-4wd-light-not-working-2001-xl.html

http://www.suzuki-forums.com/1g-1999-2005-vitara-grand-vitara/43439-4wd-freewheel-air-pump-teardown.html#post264222

The first thing you're going to need to do, is confirm what does the 4WD control on your '99 GV - the 4WD controller may be a separate module under the driver's side dash or it may be incorporated into the ECM that runs the engine (and transmission if it's an automatic) - I would also suggest you check the wiring between the transfer case and the controller, and also the controller and air pump, and the air pump itself before condemning the controller - part of the controller logic is in the way pump module is wired.

If you do have the separate 4WD controller - for a 99 GV, it should be p/n 38885-65D00 and SouthWest Suzuki list it at $104.10.

Fordem, that is impressive.  I should have gone to you when I was shaking out my electronics.  I was just going to tell him to try Craigslist, but for that much why not just get it done.  It would cost more than that to eliminate that system.

Just make sure that you check the system wiring, switches and pump before you obligate to any sort of "controller" purchase. 9 times out of 10, the problem is not the controller, in other words.

Another note of caution...from what I have read, North American sourced (US and Canada) GV's with the 2.5 engine do not use a stand alone controller, but incorporate that function in the main ECU.     Do you have a 2.0 GV???

Do you in fact know that you have a separate controller?  

Have you gone as far as to determine if your pump is actually energizing, although not providing the 4WD engagement function?

BRD HNTR - thank you sir - that means a lot coming from one of the more seasoned veterans such as you.  I assume is with reference to the tear down, because looking up a part number is nothing.

Max - that part number actually came from the parts catalog for a US market 99 GV - but - as far as I can tell - E33 (California) market cars, the 2.0 Vitaras and all US product from '03~'05 had the 4WD controller integrated into the ECU, so some did some didn't and whoever is working on the system needs to check.

I like to thank you guys on this forum you certainly have a lot of good info.
I started checking things out and found a wire had been chewed by some critter,i suspect a mouse or squirrel. I soldered the wires and everything is working good.

Good! An easy fix.