Totally agreed. And therein the problem with under-specification. (We repliers provide various possibilities & the OP must eliminate & decide.)
My experience is that LEDs consume less than relays (relay coils are usually 50-200mA) and that IGN and light circuits have the capacity to handle added LEDs.
For LEDs, generally it's only when novel combinational switching/control is required that relays etc are required.
And whilst I'd generally suggest relays rather than "power" diodes for other loads, where LEDs consume under 1A I reckon 1N400x diodes are fine to power the LEDs directly for simple combinational control (ie, omit the relay since diode current and voltage drop is not an issue).
Of course the main thrust of my original reply was to use phantom or virtual (or whatever the heck they should be called) grounds to control the load. EG - LED+ to IGN +12V, and LED- to the beam +12V (or hi & lo beam +12V) so that they are off when beams are on ad on when IGN is on & beams off.
That assumes the beam or hi/lo bulb resistance to GND is much lower than the LEDs.
The same is done for flasher beepers - eg, motorcycles - just a buzzer between left & right flasher +12V feeds (assuming flashers are light bulbs).