the left valve cover you mean the driver side right,. your putting a sohc on a 91 ranger, ok, the sohc engine have 3 big connectors plus the ecu already connected to it , ok, the 2 smaller connectors are for oxygen sensors and for transmision sensors, if your not using that kind of tranny you will not use those wires, from those 2 connectors you just need the wires for the oxygen sensors,. ok, so, the other and biggest connector on the valve cover, that one goes to the main fuse box, all the red wires go to the main pcm relay, that relay when you open the key sends a 12v signal to all those red wires, you need to connect to a constant 12 v the ecu memory, that is the yellow or yellow light-blue wire, the red light-green its a switched 12v to the ignition coil, what else, let me think with that it should fire up
its easy to know if the engine will fire up,. once you open the key or turn on the main sw, almost all sensors on the engine will have a 12 v signal, check that before cranking the engine,. open the key, then with a voltmeter check the maf, fuel injectors,. oxygen sensors, these receive a 12 v signal when you open the key, the camshaft, crank, air temp, coolant temp, throtle position sensor these are connected directly to the ecu, they are not switched, so you can check those with the key off and just check for continuity with an ohmeter, so, in order for you engine to crank up or turn on, fuel injectors on, oxygen s,. maf, FUEL PRESSURE, and it will fire up, if your test goes ok on all this and the engine doesnt fire up, its the PATS the problem, well, it will be from the begining if you havent done anything on the ecu, it will not start at all, the pats is found on ecu's from 98 and up, the only way to get rid off is to have the ecu reprogrammed with a chip,. ok,. good luck.