Shift On The Fly Switch...
 

Hey Guys,I had to pull a guy out of a rut the other night,went to put it in 4Hi and nothing,no 4X4 light on the dash or anything,what is the likely cause...fuse maybe,I haven't had any other issues or messed with anything else for it to be a fuse though...thoughts.....It's bad because I had to use Aprils' Tahoe to pull the guy out...I wasn't happy about that but of course she got some jawboning rights for a while...LOL

I would check the fuse box under the dash, #28 loc.. 10A. Also check under the hood fuse box, #17 location, 30A.

Also check the relays under the hood.

My 99 4Hi and 4Lo relays are in this box. I was having a problem going into 4Lo and cleaned all the spade connectors on the relays with emory cloth and it started shifting into 4Lo again.

http://i288.photobucket.com/albums/l...g?t=1287627739

Can you hear the transfer case shift motor operate? If not check the connector at bottom driver side of transfer case.

Nope, I can't hear anything engage,like the switch is just dead.I haven't used it in a while,but the last time I used it,it worked.

Check what Clint and I have suggested and let us know what you find and we can go from there.

How long is "a while"? Months? Years? I do Guzzle's auto hub maintenance annually, but then, here in CO, it gets a workout in the winter months!

Hubs have only been on for a few months now,I used 4x4 back over the winter a few times,but not since.After b-fast I'm going out to check the fuses and relays,I'll post back what I find. Thanks guys...

Your vacuum lines could be leaking causing your hubs not to lock in.

Ok guys,I think I figured it out.
http://i245.photobucket.com/albums/g...g?t=1287666744

Notice relays A&B,I was told buy a dealer(I know,this is what started it),that these two relay slots were for the charge line for my TT,so I bought these two relays and put them in and I guess the charge line wasd working this summer while towing.Well,after reading the replies from here I go out and switch relays A&B, with relays C&D,checked my SOTF switch and it works.Obviously A&B are for the SOTF,but are the other two for the charge line?,if not what are they for?......Thoughts...

OH boy,sorry guys,I have both sets marked A&B,C&D are the ones to the right...GOOD GRIEF CHARLIE BROWN.

Is your power windows working? After you check the fuses and if the are ok,maybe a wire came off the back? Reason I ask about the windows,when my GEM fried, it wouldn't light up for the 4x4 either. I also had a wire to pull out of the plug before is the reason I mention that also. Hope its something simple and easy to fix.

Phil,

The ones closest to the firewall come with the trailer tow package.
They are for trailer batt charge and I belive trailer back up lights

The ones toward front of truck are for ESOF. These relays should have two sets of contacts in them, one make and one break.
The ones for trailer tow only have make contacts. You can't swap them.

Both ESOF relays in my truck are FOAB-14B192-AA.

Bottom side of relays.

http://i288.photobucket.com/albums/l...mWithAnnot.jpg

The ESOF relays have 5 posts. When relay operates contact 87a opens and contact 87 closes.

The trailer tow relays only have 4 posts. There is no 87a.

There should be a schematic right on the relay showing the contact arrangement.

The five post relay will work in place of the 4 post, but the 4 post will
not work in place of a 5 post if the break contact is used in the circuit.

Hope I haven't confused you.

Sorry for taking so long to post back guys,I just got back in town a few mins. ago.Thanks for the help,so can I switch the two relays closest to the firewall with the other two,I know the ESOF will work because I switched them and it worked,but will the other two relays work right for the trailer towing?

They should Phil. All you need are two relays with just make contacts.
In other words the 4 post relays should work for trailer tow relays.
5 posts will work as well if the trailer toe relay socket has 5 female sockets.

Robin has your answer.

The relays shown in the ESOF "doghouse" are SPST relays, which should be SPDT.

IF the Trailer-tow package relays are SPDT, and you swap them for the ESOF ones, everything should work afterward.

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