WE have a 2003 diesel with the second 6.0 engine in now. Ever since the new engine has been put in we have had alternator problems. We just put the fourth one on this morning and it still won't start. Garage says we may have gotten a bad one but this same thing happened three months ago brought one home wouldn't start returned it got a different one that one worked for about three months and it's go again already. They have looked at it many times can't find any thing wrong.

Thoughts:

. Remove and fully charge each battery.

. Clean connectors going to the alternator and to the mega fuse in the under hood fuse box--apply dielectric grease.

. Check ECM and alternator FR (Field Response) Signal. The FR signal communicates to the ECM how "hard" the alternator is working to meet the electrical demands of the truck. This square-wave signal varies in pulse width, according to the load on the alternator. The ECM places, approximately, 5 reference volts on the wire. The voltage regulator will drop this signal to approximately 1.2 volts, in proportion to alternator load. The ECM compares the electrical load (ELD) signal with the FR (Charging Rate) signal from the alternator and uses that information to set the idle speed and turn the alternator on and off. This helps fuel economy. Problems with the ECM, though rare, can trash alternators.

. Install a new Motorcraft alternator, not an aftermarket product.