i have a 99 f250 super duty gas - 4 wheel drive will not work

yup, lift off the block that your shift relays are plugged into, you will find greeish/white powder around the weep hole. the conductor has corroded UNDER the relay socket. repair socket, good to go. in the short term, you can take the cover off both relays and simply push the carrier close with your finger to kick the shift motor, this is all of course its not the shift motor itself. if thats the case, 2x 10mm head bolts, take it off and use a cresent wrench top shift the transfer case

no corrosion under the relay sockets, replaced the shift motor an still not working. Its not throwing a code what so ever, the button to flip in 4 wheel drive on the dash board has no power to it at all. any ideas ?

To check all the circuits to the motor take a pair of the relays and pry off the black cubes. .. you will be able to shift it manually by pushing on the moving part of the relay. Each shifts it to in or out of 4/4. if it functions I would then get a new shift switch.

On my 99 f250 they are a bundle of wires on the front drivers side wheel just above the frame it y's off to your 4x4 relays. Mine had 3 broken wires where those 3 bundle of wires come together!