When I first got my LGB F7 units years ago I was dismayed to see how much power they took to move. I couldn’t get them to move at fast-passenger-train speed at all. I put them away and have not used them till recently. Now I am converting to battery operations and I started working on them. Due to some frustrating circumstances, I ended up bypassing the main circuit board completely. So my battery power input went directly to the truck power blocks. That meant that I lost my lights, but was still able to run. To my utter surprise, I found that these units then operated at excellent speed. Why would this be? There is some sort of donut shaped gizmo on that board with wires wrapped around it. I can only imagine that thing was sucking some huge amount of power. But to what purpose?
So that lights (and sound if fitted) could come on before the loco moved, there was a circuit that bled off the first 5 - 6 volts.
Put an LED headlight in it with the appropriate resistor (Depends on your battery voltage) and you’ll have a nice bright headlight again.