It may just have been spitting out a little excess if you filled it too high.
- E-fan should not be drawing enough current to dim lights though, especially since you have a 100A alternator (internal regulator?). Need to check that out.
- Main power line going directly to battery or ignition-run line?
- Size of in-line fuse?
- Fan pushing air into radiator or pulling it from radiator?

I've been using an electric for over a year and it helped tremendously.