You did it correctly, however a 40watt LED bulb does not use 40 watts of DC power. Rough guess 6-10 watts. From your measurements, your system is working well.....extremely well. Now it's only a question of how much capacity you have. As a suggestion, if you can temporally connect up an old HL you have laying around, or exchange your tail light bulb with a 1157, you'll be adding in more load than you'll ever see from LED lamps.