When the PCM wants overdrive, it grounds that circuit. You want you test lite in line with the ground side of the circuit. (or, just tap power somewhere, and put the other end of the test light into the wire going back to the PCM. Lite on means the PCM wants o/d.)

 

Hi, put trans back together and still the same no 3-4 shift. But is now showing codes p0753 and p1765. Tried different relay. Relay out, has 12v on 1 and when started 13ish on another. At highway speed stays in 3rd but if you let off the gas rpm drops nearly to idle and comes straight back up if you switch od off. Bearing in mind I'm a graphic artist not a trans guy, is there more testing I can try
​​​​​​? Thanks for your help so far

 

Hi, put trans back together and still the same no 3-4 shift. But is now showing codes p0753 and p1765. Tried different relay. Relay out, has 12v on 1 and when started 13ish on another. At highway speed stays in 3rd but if you let off the gas rpm drops nearly to idle and comes straight back up if you switch od off. Bearing in mind I'm a graphic artist not a trans guy, is there more testing I can try
​​​​​​? Thanks for your help so far