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My 2005 ford focus automatic transmission with 90000 miles does not have second gear. Transmission does not want to shift from 1rst to 2nd. When it does second gear does not engage and engine revs. Took it to the ford dealer and after 6 weeks, a new computer, and $1000 they told me it was the wiring harness, and it would cost another $3000. Since I'm and electronic tech, I figured I could troublshoot the harness myself so I brought it home. I have the ford service manual, so I looked up all the connections and checked the harness. No problem with the harness. Resistances are within specs and Voltages are applied to the transmission connector at the appropriate times (although the manual does not say what the volatges are suppose to be). Solenoids A&B have 12 volts and C,D,& E have 1 volt. Since solenoids A&B are different part numbers than C,D,E maybe they should have different voltages applied. I also have a code reader and get codes P0750 solenoid A, all the time and occasionally code P0755 solenoid B. I checked the resistance of the solenoids and they are within specs also. I would like drop the pan and apply voltage directly to the solenoids to determine if they are functioning. Since there are two different types of solenoids, they may take different voltages. Does any body know what voltages are to be applied to these solenoids? Does anyone have any suggestions as to what may be wrong?  

First of all the dealer told you it was the computer? And im sure they billed you diagnostic time and then after they installed a computer they said it was the harness?
And you paid them? How do they get away with that crap? An independant shop would never get away with that! Anybody can play hit or miss. I would expect more from the dealer.

I dont think PO750 and 755 are  electrical failure codes. Those codes set when the gear ratio of the trans is not what it should be for what the computer is commanding. So it would be a mechanical solinoid malfunction {not electrical}but since you have solinoid A and B codes your problem is probably either  a bad valve body or most likely a burnt transmission. Drop the pan and see what it looks like.  then post again.  

That probably won't tell me much since the ford dealer also changed the oil and filter. That was there first guess at the problem, although I don't know why since it was changed less than 15000 miles before that. The oil looks and smells good on the dip stick. I did check the oil before it went to the dealer and it looked and smelled normal then as well.  

If you get going fast enough ......maybe down hill does the trans catch third?
if you had a broken band or accumulator or if one component was burnt the fluid and pan might not show any evidence of that. I would clear the codes and then drive it with a scanner in data mode and see if the computer is commanding the shift to 2nd.From what your describing it sounds like the computer is commanding the shift but the gear is not there. Another thing you could try is going to a transmission shop that has a device that will bypass the computer and shift the trans.{like a Transx}
that would positively eliminate or verify the trans as the problem.  

If I feather the gas and the trans finally shifts out of first at about 25 mph then it slips for just a second and then goes into third. If I then give it more thottle so that is should down shift into second it then slips again when it down shifts.  

So then the trans system is shifting into 2nd but 2nd is not there.You most likely have a broken band {intermediate} or a problem with the servo that operates the band or possibly a problem with the accumulator for 2nd. Basically a damaged band or a major hydraulic leak in the 2nd gear circuit.  

If that is the case then why do I get code 0750 solenoid A. I can turn the ignition on without starting the car and erase all codes codes. Then start the car. Code 0750 will appear in about 20 seconds. The car was never shifted out of park. Solenoid A is suppose to be on in Park, Nutral, When manually shifted to first, and, fourth.  

You know what?  I mixed up ford diagnostics with toyota  sorry.When im on here i have no referance material i have to go from memory sorry again. PO750 is electrical.
when the key is on ssa should get 12 volts. when you start the engine the computer turns on the solinoid by making the ground for the circuit.Do you have a pin location chart for the computer harness connector? Check continuity on the wire for the ssa ground circuit.{0 ohms or almost no resistance} Since your getting 12 volts at ssb also {PO755} check the ssb ground wire continuity also .check them  both  from the trans connector to the computer connector.Maybe they run right next to each other and they are both damaged.Also look on the wiring diagram and check any wires going from the computer to ground.
if all that checks out ok then you have to check the continuity of the internal trans harness ssa and b ground wires {or you could check that first}  

The wiring checks out from the computer to the trans connector for all solenoids A,B,C,D,E (less than 1 ohm). Also have 12 volts on the trans connector when in park on solenoid A, and 12 volts  on Solenoid A and B when in manual First, which is correct according to my manual. Solenoid A should be on in Park and all others off. If A wasn't on (All solenoids off) the manual says it would be in third. Vehicle appears to be in park/neutral not third so I assume solenoid A is ON.  

If solinoid A was off in park the trans would not be engaged because when the manual valve is in park the forward clutch is off {they would never design a trand that would engage in park if a solinoid failed} .If the Solinoid A and B ground wires were good up to the trans connector and all the computers grounds were good then you have to check the trans internal harness next .  

the a solenoid is bad  good news is that its only $45 at your local dealer.  easy to replace  just drop the pan they are right inside there are 6 of them  the one with the white wire is the a solenoid.  very common problem