i have a 1995 f150 with 4.9l 300i6. i blew head gasket on old motor so put new/used motor in, same 4.9 300. got everything hooked up, set timing and all that and it wont start. i have spark, compression, and fuel to the rail. new fuel pump and filter did nothing. took it to the shop and they replaced a couple parts to get the pressure right and i couldnt afford to keep it in there any longer. he said he doesnt think the injectors are pulsing. i checke a few wire coming outta the harness and theres a red with white tracer that has very weak signal.. what does that wire go to? and more ideas what i can do?

 

Did your replacement motor come with a partial wiring harness attached to it? If it did and you used it that is most likely your problem, unless the motor is from the exact same year and class of truck(F150,F250, etc) the engine wiring portions are not compatable, so you will either have to get wiring diagrams and sort out the differences or just put your old engine harness back on.