My 87 300zx has developed a case of the dim headlights. They don't get brighter as RPM's increase and the alternator is fine. I have OEM bulbs installed, have tried HID no better. Have a direct to battery harness from Black Dragon. Think that will improve my headlight situation?

 

Have you checked the wiring, connections, fuses, and headlight / combo switches?

 

I have never heard of headlights dimming unless the alternator, or, the battery was dieing.

Normally the switches crap out and only one light will pop up and illuminate, but, no one has ever said their lights just dimmed. Most of the time switch problems can be fixed by taking the steering column cover loose enough to get the squirt tube from a can of CDC Electrical Connection Cleaner into the switch. Put an old towel on the floor to catch the fluid, and, flood the switch from every angle possible. Most of the time the switch will begin functioning normal again. I don't really think that is your problem, but, it's a cheap thing to do that might help.

A weak ground could be the cause. Have you cleaned the battery post lately? Check all of the grounds you can find on the car. If corrosion has set in, it may be resisting the flow of electricity.

It isn't a fuse. A fuse is either good, or, it's blown. No middle range of operation.

Good luck... Keep us posted on the progress.