I ran the 10a version with no trouble what so ever. I wanted enough power in case I added a radio
DROK 10 amp
It powered a 12v relay (for isolation), a 12v tach, a power port that I would use for a Garmin and/or charge my cell phone plus it powered an inverter that ran a couple strings of Christmas lights.
Never had a problem with the trucks 6v system nor the added 12v circuits.
Remember to fuse everything for "just in case".
Dave

1949 Chevy 1/2-Ton 3100
1949 GMC 1/2-ton 100
In the Stovebolt Gallery
More pix on Photobucket
Video of the 216 running
Video of a Winter Cruise