head lite on the dim side

more gobblins as halloween nears i guess..my head lite is bright on high beam but is very dim on low beam. when i rev up the bike then the low beam gets brighter like its on a magneto bike...has anyone ever had this problem?,,,tia    1979 kz1000ltd  all stock
 

What is the battery voltage with the engine running and what is the voltage at the bulb connector with it connected and working 

ok ill start looking there first
 

Sounds exactly like what happened to my gpz550. The low beam of the dual-filanent h4(?) bulb had gone bad and needed to be replaced. I dont know if you have the semi-sealed headlight, but if you do, take the bulb out and inspect the windings for the low beam. The one on my gpz550 had become all frayed. If the bulb is fine then wookie can probably help you more than I can.

For a quick test while you have the headlight out of bucket, switch around the High and Low beam connectors. Note if situation switches to the high beam and low is correct. Your selector Hi/Lo switch on LH handlebar switchblock is just a SPDT sliding switch. These switch half-moon terminal wafers can warp or the factory soldering can fail resulting in a voltage drop or..just corroded.

Here's some photo examples of what i was talking about. If you do find issues in this sector and your knob selector is still intact, Don't remove the phillips headed retaining screw! Most likely to just fall into pieces upon disassembly! A BAD decision used by the manufacture using sliders of brittle plastic since 1975. Just remove the wafer straps and slide out for any repair.