I'm running an 8ft plow on an 04 f350. Recently, when out plowing the battery light came on. It comes on and off. I've tested batteries which are fairly new and they're at full charge. Taken the alternator out twice and had tested twice at O reiley's and Auto Zone. Both said alternator was good. Not too confident in them as they seemed like they struggled with the tests. I have noticed last night when reconnecting the plow that the dome light dims when pressing buttons on plow control. I still think it may be an alternator issue. Any ideas or past experiences? Should I go with larger altenator?