Someone with an EVTM (shop manual) please help

[dixie281]

howdy all, can anyone provide me with an electrical schematic or more helpful would be a connector pin chart for the electric 4x4 shift control module on my 88 Bronco II? It's a 2.9L, auto, Eddie Bauer if it matters any.

If you wanna read, here's what's going on. my pain in the a55 electric 4x4 is actin up again. This time it ain't a blown fuse, or not one that I can find. Fuse links don't seem to be burnt either, again at least the ones I could find.

I went out last Saturday night with the wife, and we rode around the woods and had some fun...drove thru a couple mudholes and mostly rode trails. Don't recall ever having to use the four wheel drive, but I was pretty well trashed by then. My wife was driving and she don't remember using the 4wheel either. Before we headed out I did check to make sure it worked, which it did.

Now, a few days ago I needed my 4wheel drive and when I selected 4Hi at the switch, the relays in the dash made a repetitive cycle sound, like it was repeatedly trying to shift and failing to do so. I listened under the truck and heard the shift motor trying to work, but it seemed that either it was jammed up or the controller was telling it to go back and forth between 2 and 4. I tried to shift it while driving real slow in reverse and forward gears, and eventually it would engage 4 Hi. Never tried 4 Low. Put it back in 2 wheel (which it did every time w/o a problem) and left it til later.

And now yesterday I get to working on it, and it won't work at all. No relays clicking, no shift motor, nothing. All fuses still look good to me.

and here's something...I didn't like the 4 wheel drive control on the overhead panel so I moved it to a rotary switch on my console and wired the 4x4 and Low Range indicator light circuits to the respective lights on the warning light panel between the tach and speedo. I think these light are only used when the truck has manual 4x4, but I wired to here because I like it that way. They are incandescent (non-LED) bulbs in there, and at night I can see the 4x4 and Low Range lights glowing softly together. If I hit the brakes they get a little brighter, but not full brightness like they were on or something. If I try to engage 4x4 Hi or Lo they go out til I release the switch. The only other time I have seen this is when I had a blown fuse somewhere, don't remember which fuse or what it was for but that cured it.

So again, I would really appreciate a schematic or connector pin diagram of the 4x4 shift control module. I want to check for power and ground continuity, then we'll worry about inputs/outputs. And of course, any and all suggestions are welcome. Next truck...MANUAL transmission, MANUAL four wheel drive, and MANUAL front hubs!! :-)

thanks
Andy

[oneway]

sounds like you could have wire to wire contact somewhere or crossed something up. If you hit the brakes and they light up - check the wiring you did. You could see if the truck will shift into 4x4 by pushing the brake and hitting the 4hi button. If that works - then there's the problem. Perhaps not enough power is getting to the switch/relay/motor to engage it - applying the brake increases the power demand.

I'm looking at a wiring schematic and pin chart for the 90 2.9L electric 4x4. Let me know if that will help and I'll find a way to load it or get it to you.

[dixie281]

Well I done found an electrical schematic after some thoughtfully worded google searching, and I verified that the ground and continuous power connections to the shift module are working, but no switched power is available at the connector. I jumpered power to the switched power input from the continuous power input, and now the module is back to doing what it was doing in the first place...seems like it's trying to shift but gettin jammed up. This weekend I'll pull the electric actuator and drive assembly off the transfer case and see about possibly bringing it back to life. Probably just the feedback position sensor's got some dirt in it or something.

I'll let y'all know what happens...

EDIT: oh by the way thanks for the suggestion oneway, but now that the module has power restored, the indicator lights stay off like they should. Something about the module not having power makes those lamps glow real dim. Leakage current maybe?? I don't know, but thanks for the suggestion :-)

Andy

[RakerBill60]

Could be a grounding problem, or feedback through the control switch you wired in. Check all connections really good, and check voltages in and out of the switch. Then you can check resistance through the switch as well. Usually when lights glow like that there is a ground issue.