So have f250sd v-10 and its giving me a code p0356 and Ive changed the coil on cyclender 6 and it still shows same problem Brought it to a garage and they said there was no intermitted spark on one side of the plug for the coil so they said it must be a broken wire or bad computer so Ive been looking for the computer couldnt find it so I go to FORD they said it was in the middle of the dash So I tore it all apart to not see computer to check contanuaty cant find computer Can someone help me out

 

Ford places their ECM's all over the place. They even change mid year. What year is the vehicle?

 

If this is like around and earler '00 series, it would be along side the e-brake pedal up against the firewall (most likely). However, they did change to anywhere a few free centimeters were availible.
Be careful here. Make sure that there is battery voltage to the specific coil connector on the red wire (hot at all times with KOEO, KOER) with a test light (use an old 1156 or 1157 bulb; you do need a little bit of amperage here). Most likely, there is a wiring issue with the ground side (the other color wire, it could be any color) that goes back to the PCM for the coil driver. They had a habit of breaking wires right at the connector, but an open could be anywhere.
If you check it all out and there are no opens, then it could be a PCM problem. This code means that the PCM did not see batttery voltage at the pin in the PCM. The voltage is always availbile from the battery to the coil; the PCM only provides the ground. If it doesn't see the 12 V at the pin in the PCM, the code is flagged.