Dim headlights are almost always the result of a poor ground in the HL wiring system.
I agree here most definately. Check the power first. Make sure that you are getting all of the volts you are supposed to get across the back of the bulb - then check your wire ends and switches for clean, solid contacts. If you are using sealed beams, get rid of them - Halogen replacements are available for every type of fixture (even the historic type nowadays). Before putting in halogens though I would recommend looking at the wiring again (this time wire size). I would go very overkill with the power supply wires to the headlights (I wouldn't want more than 1/2 a volt drop from the batteries to the bulbs). You need to make sure that the wires are sized properly for the load size, so that the resistance charactersitic doesn't come into play.
For example, a 12Ga wire has approximately 0.00158546 Ohms of resistance per foot. Using Ohm's Law:
We extrapolate that for a pair of headlights (assuming two 55-watt low beams @ 12VDC) will cause about:
110watts / 12volts = ~9.16Amps
9.16Amps * 0.00158546Ohms = 0.0145Volts per foot drop (assuming they are the only load on the wire).
If you ran a 12Ga wire from the back of your bus to the front (my batts are in the engine compartment), you would have roughly a 0.5075 to 0.6525 volt drop (for a 35 to 45 foot bus respectively, this excludes your chassis as a return path - we are asuming it is a "perfect conductor" with NO
corrosion). On a 12 volt circuit, for the 45 foot bus, this would already be a 5% drop in system voltage at the bulb (which is considered "marginal"), and the bullb will dim very quickly with more resistance (be it from corrosion or whatever). Assuming you have a corroded ground, wire, or bad switch that is further dropping your voltage - you will have terrible lights in short order.
This is as best as I can manage to illustrate the importance of maintaning your wiring/grounds...
I switched my 7 over to 12v rectangular halogen.Much easier at night. My old 24v's, even though new, were just too dim. I didn't think about it until I was done, but are there such a thing as 24v halogen? It would save you some trouble. Jim.
Hella makes 24V H4/H3/H1 bulbs. Osram sylvania makes them too (I believe under the "truckstar" label). I have replaced my 6x8" DOT fixtures with Cibie ECE fixtures (Left-hand-drive beams and with 24V H4). This was a change from a 12v system, and by leaving in the 12Volt-system-sized wire, and double checking the grounds, I was able to reduce the voltage drop even further (now it's measured out to a 0.23Volt drop, down from 1.9V).
The lights are bright but have a really nice sharp cut that slants away from on-coming traffic, but gets light onto the sidewalk or the ditch on the side of the road. I also noticed that the lighs have a lot more fill imediately in front of the vehicle, which has allowed me to run without my fog lights on all the time.
Some states may fail inspection if the lights don't say "DOT" on them (ECE would be a fail), but other states (especially where there is lots of fog) allow ECE - and others simply don't fail it if they see ECE. I think everyone should call their senator and congressman and have them change it for ECE being a global standard. The beam patterns are better, and it would be cheaper for car makers to only make one type of fixture (ECE is used in more places in the world - go figure, WE are the slow adoptors). Like in Europe, we now have very high retro-reflectivity requirements for road signs, ECE lights put more light way above the cut-off (so there is a "dark area" where on comming traffic sits), that is intended to illuminate those signs.
With my headlights I can very easily spot the new road signs out here.