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I got a 99 super duty 7.3. It has the automatic switch on the dash and when I go to engage it the 4x4 wont come up. Also my air/heat only works thru the defrost. I was told this was a vac pump promlem, so I replaced it this morning and it still does the samething. I took a test light to all my fuese under the hood.( Did I miss a fuse somewhere or a relay) I have no owners manual. I pulled out the switch on my dash and took a test light to it and there is no power going to it. I need help quick, a diesel wont go no where in the mud.... thanks
 

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Check fuse 28 under the dash, it runs shift lock solenoid and vacuum pump motor. Check fuse 17 under hood it runs the transfer case shift motor. And relays 41 and 42 under the hood also work the shift on the fly.
 

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also check the vacumn lines that go down to the hubs. our SD did this when we had the OEM lockouts before we went to warns. the factory junkers r vacumn operated. another one of ford great ideas.
 
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