Hi,
I have a 1990 Ford Taurus GL 3.0
Over the last couple of days when I try to start her in the morning the power fades out - no crank, internal light goes very dim - the ignition lights are barely visible. I try a few more times and give it a rest and then it starts fine! Thought it was a bad battery but had it checked by a diagnostic and it said ot was fine. Any ideas what could be causing this?

Thanks!