What he has will work but you need to turn the diodes around. The line indicates the end with cathode.

Thanks for that clarification. I can never remember which end means what. 12+ blocking this direction, 12- blocking that direction. I either have my electronic coworker draw it out for me, or I try it and reverse them if no work.

A 6 amp diode is the biggest common one with wire leads, like the General Instrument p/n GI 751, GI 752, GI 754, GI 756 ... as the number go's up, the max voltage you can use it at increases, so for 12 or 24 volt circuits the PRV (peek reverse voltage) of 200 or more is appropriate, as there are voltage spikes in the system from any inductive loads, such as starter motors, solenoids, and such.
The diode is like a check valve, passing current when the stripe or cathode end is closer to the more negative side of the circuit. (the diagram has them backwards) notice the far side of the lamp is connected to negative. in the circuit the switch that is on will pass current through the first diode, but the other will not pass it to the second circuit. I hope this is a help.
Mike