Since posting the original question I have observed a few more bizarre things about my charging system. I have the codes read on my civic which showed malfunctioning O2 sensor as well as bad speed sensor. The fuse that keeps on blowing guards the speedo and the alternator so I decided to disconnect the speedo sensor and replace the fuse. The engine check light stayed off until the engine reached about 4000rpm. So I am thinking that the speed sensor itself should not be responsible for the blown fuse. The weird thing is that after shuting the engine down and restarting it, I get no charge to the battery (12.3V) but once I rev the engine up to about 4000rpm (I have no tach so this is a pure estimate) the charging system kicks in ( I get 14.2-14.4V at the battery) and stays even at idle. (that is with the blown fuse in place).

Hi. It's been a while since your post so I imagine you have solved the problem (or binned the car!). If not - here's the very likely problem you're having and the solution:


If you look under the intake manifold at the rear of the engine there is a pack of wires. This pack rubs on the bottom of the intake and creates a short circuit which screws up the speedo, sets off the check engine light and gives a trouble code for the O2 sensor. And causes the headlights to surge and alternator to stop charging the battery.

Just crawl under the car when it is up on stands and gently turn over the pack of wires under the intake to expose the bare wire or wires. Tape them up with insulation tape and away you go.

Hope this helps...