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.             

Grab a volt meter.
Have the headlight out but still connected.
Meter on DC V

Key on Engine Running
Low Beam On

Red probe on Positive battery post (metal part of battery)
Black probe on yellow/orange wire at headlight (backprobe the headlight connector so you don't disconnect the connector. This allows the low beam to run while you take the reading)
what is your voltage?
Voltage should be as close to a steady 0.0v as possible.
The reading should be steady and not fluctuate.
If the voltage reading is not steady then your low beam filament may be broken resulting in ghost voltage(voltage readings that are not steady)
Any higher than 0.5v then you have too much resistance on the wire/circuit going from the positive battery post to the low beam + wire at the headlight.


Move your Red probe to the Negative battery post
Black probe on the Yellow/Black wire at headlight connector.
What is your voltage?
Voltage should be 0.0v as well
Any higher than 0.5V  then your connection to from the headlight to the negative side of the battery is suspect.
This tests your connection from the headlight to ground.

Turn off bike.

these are great information remediations,,,thanks guys ..ill let you know what happens