Code 43 . my alt stayes at about 11 12 volts when

First make sure both battery cables are free of corrosion and ground is secured to chassis and engine then check to see if theres an alt. fuse or bat. fuse blown. Another way to test charging sys w\out an meter is to remove the ground terminal from the bat. with the car running, if the alt. is good car stays running, if all else fails take the alt and bat to a parts store that will test them for free

Its got a drain somewhere can you find the sound?

The alt should charge at around fourteen volls , any ways, yogi need to put another battery. A weak alt will kill a good bat.and vise versa

your battery needs replacement, it may show 12 volts but the amps aren't being charged enough,, if you take the battery and have it load tested,, you will see that one or more of the cells isn't charging correctly,, if the battery checks out ok, then with the truck running, place test leads on the pos and neg battery terminals,, you should be seeing a reading of 13.5-14.5 volts,, if not your alternator is bad, if you do,, its the battery for sure , make sure also that all the battery connections are clean and tight ,, dirty or loose connections will prevent good charging

You'r new alt. may be bad? Have it checked. Have you'r bat. load tested

Altenator good? Did you bother to check the diode in the altenator? If its blown it will not let the voltage regulator charge the battery. The only way to check this on the engine is to have it running. Take a volt meter and check the voltage while running. If 13.5 volts shows it may seem to be charging the battery right? Maybe not. That the probes from the volt meter and invert the probes from red to the negative battery terminal and the black probe and connect it to the positive terminal. While running if the same voltage shows the diode is bad. The diode prevents the current running in reverse. If running both ways no charge is getting to the battery

Check the drive belt tension and wiring connection at the alternator and at the battery. Check for a blown fuse in the fuse block . -hope this helps

2 problems, first you have bad starter or starter relay for starter staying engaged, keep alt plugged in has nothing to do with starter staying engauged, to test starter relay, jump at relay bat + post with red/bk wire on solonoid, if cranks over without staying engaged, then not relay or starter but rather in your ign switch, ford had bad problems with ign switch some years ago doing that

check the alt and the bat

it seems a little bit low allan normely its around 12 / 13 volts with it being a diesel as well there a bit harder to start