If you are getting a clunk when you go into first, it is not the diff, its your clutch not disengaging fully or you shifting into gear before the input shaft stops spinning which then makes a clunk at the rear. Try going to 2nd or 3rd first then go to 1st, clunk won't happen once input shaft stops.
Update: through many uses of the test light, multimeter, and studying wiring schematics, I found the issue. This little fuse link is shot..the EEC was getting power but no trigger for the relay, coil, or injectors..all relays tested and working, TFI module good.
Need a little help…Car will not start. No fuel pump prime, no power to the coil, no power to fuel injectors. Turn the key, all dash lights come one, try to start and she just turns over and over, not any type of fire. It just died while driving down the street and hasn’t started since...
Replaced the solenoid pack with one from Ford, it did not fix the problem..didnt even drive it.. it started while the truck was idling. I cleared codes and it all came back..I am at a loss..