Lights dimming

[atavar]

I've been noticing for a while now that the main lights on my '08 Norge are getting yellower and dimmer.  They used to be the best headlights in the world. 
The problem started being noticeable some time before I replaced the battery so I don't think it is the battery itself or the connections at the battery. 
I haven't started troubleshooting yet and want to form a plan of attack.
At this time my plan is to connect a battery charger and just start chasing the wires with a voltmeter starting at the battery looking for the connection or relay or switch where the voltage drops. My main suspect would be the relay that turns the lights on after the engine starts.
I cannot accept that all four main bulbs are aging and getting weak at the same rate.
Does anyone have a link to a wiring diagram for the '08 Norge?  That would make things much easier.  Any advice is solicited and appreciated.

[organfixsing]

Try this. http://www.thisoldtractor.com/guzzi007/sportissimo.html
Be sure to get the right one. There are diagrams for ABS and Non ABS

Cheers

Brian

[Idontwantapickle]

They all may share a ground, good place to start.
This old tractor will most likely have a wiring diagram.
Hunter

[Farmer Dan]

First thought in my mind would be to check the battery ground and where it grounds to the frame.  While your at it might check all the ground points on the frame.

[Kiwi_Roy]

They all may share a ground, good place to start.
This old tractor will most likely have a wiring diagram.
Hunter

Don't forget also the ignition switch, the lights go through there also even though there is a headlight relay

Measure the voltage between the engine case and one of the black wires in the headlight (Voltage drop in the grounds)
Battery + and the headlight.
Battery + and one of the 3 top fuses