Let me throw this out there. I found the same problem with my B7800 and those weak bulbs they use. I like LED lighting and came across these LED Units "MR16" Indoor Floods, rated 3.5watt @12v and 185 Lumens, they were about $6ea. Although worth noting on the back of the module it states it is "Suitable for Damp Locations", which I think behind the grill and under the hood would be less than damp.
Now I realize these are not direct replacement units but what the heck, let's face it the originals just don't cut it so not much to lose. I did this some time ago and took a few pictures which better show the process but I will dialogue it below.
I removed the complete reflector/s from the tractor and discarded the original blub and socket. - NO GOING BACK NOW - Next I took a hole saw, just slightly smaller in diameter then what the LED unit is, and cut right through the back of the housing.
Next I drilled a pair of holes (1/16"dia) around the opening at every quadrant.
Using some stainless wire make just a simple tie for each pair of holes. The new light module is made with heat sink fins (openings) all around the circumference, which makes this easy. "Twist Tie" the module over the hole you made in the reflector at all four positions. It's not exactly aerospace but for a tractor it works.
Now to connect it up, having clipped off the original bulb socket just strip back the wire, slip on some heat shrink and solder the wires directly to the pins of the LED Module. Make note of the polarity, if I remember it is relevant to these modules. That's it, only really takes maybe 10 minutes per headlight to do this mod. Made quite a difference in light output and still looks stock (on the outside). I didn't use any glue or sealant on the bulb as if they ever needed to be replaced just clip the ties and replace the module.
(See next post for more pictures)