Ck wireing! My 99 f250sd quit charging. Used multi meter to prove batt lite wasn't erroneous. Check alt. .....still no ch. Use this site to test sys. Got to pin test L. Took it to a.good mech. 30 min later wa la..juice! Wires attached to solonoid on inner fender pass side were the issue. They are grey on my trk. Didn't look bad. BUT THEY ARE. REPLACED WIRE ENDS, ya the thing with hole in them and It is charging as it should. One of the wires is the fuseable link, runs under batt. Link was.ok best 65 dollars I ever spent. I was told sometimes the fuseable link goes bad too. IF u replace it solder the wireing. Use shrink tubing. Hope this helps someone.