4th gear in drive range won't engage

[miked50]

Aisin warner 0372L auto trans. been a problem from the moment i had the truck. engine originally is a g54b then replaced with a 4d56 turbodiesel when the gasser run out of blood throwing a rod on its block.

i had the impression that the aisin tranny is fully hydraulic/mechanical whatsoever and doesn't need electronics to do the shifting fulltime or part time. what could be the problem? does it require something like engine temp, trans temp, etc. to process the shifting? i really am not sure about it. i found the ECM a year ago on the passenger kick panel when i was doing some AC blower work on it. maybe the g54b used it (ECM) but the 4d56 didnt require one. the former owner did the swap fyi.

[pennyman1]

there is a wire from the auto tranny that needs to be grounded for the o/d to engage. The gas block intake has a temp sensor installed to only allow the o/d to engage when the engine reaches operating temp - you can just ground the lead and the o/d will engage whenever the o/d is turned on on the shifter

[miked50]

will search that "magic wire" then.....it's a spaghetti mess under the hood. thanks

[pennyman1]

it is right around the base of the carb - black in color, not that that will help as all the wires there are black already...

[miked50]

fyi its a diesel horse already. i'm pretty sure previous owner's mechanic who did the swap have no idea of whats gonna happen with the overdrive circuit. maybe he just cancelled all the wires which is really annoying. so im on my own on how to figure it out (with some help from here of course). the OD switch still functions as well as the OD off indicator lamp on the quadrant and OD on indicator on the dash. checked also the overdrive relay on the driver's kick panel, its alive. another thing, the OD off lamp keeps blowing out. afaik, i replaced it twice. didnt bother to change ever again.