OK. Ya! bread boards are OK for the smallest of projects, IMHO > not suitable in this case though. I mean, your going to spend as much time if not more doing point to point soldering as you would just drawing your circuit on a blank, etching and drilling. I have done it both ways (also wire wrap, which is nice in its own way but eats a lot of room).
Also, if you have not read. Research the diff tween incandescent vs. LED. Now above is just a post, but I think your making some common assumptions/mistakes. Incandescent light is spherical. LED in planner. Hence, LED is MUCH dimmer than incandescent, unless the viewer pupil is equal to the plane of the LED. That is why LED are not rated in candlebra's. Your intending to put a LED source into a reflector designed for incandescent. It is not going to work very well. Others have tried it and report the light output is weak (it's not weak, it's that the emitted light is not focused and is lost). I would recommend before you do anything, you insure your light source works within your reflector housing (do you have a hatch by chance?). I have a hatch, and I have already worked out that, for the rear turn signal/brake, using the stock housing/reflector. The only way to convert to LED (that work as good or better than incandescent) is to use two 20MM LED, mounted back to back. The brake light LED faces the reflector, the turn signal LED faces out towards following cars. Both require 120degree light spread. Hence for the brake, simulated spherical light into a spherical reflector. So it 'should' work. This is all the 'crap' you get into with LED. (I am lazy and just use the incandescent bulbs). But you need to work this all out 1st so that you don't spend a ton of time on something that in the end does not work.
add >> GEM >> just to be clear. Your still going to put a resistor on the output of the GEM module as it requires a minimum load to function properly. Your going to use the signal to trigger your 555. You don't really need to worry about impedance. So no harm to your GEM. You will need to have the 555 drive a power transistor (555 can do this easily if common cathode). The power transistor is what drives the LED. If you use discreet LED, and because the turn sig is pulsed, you can overdrive the LED by ~ 2 volts (never exceed the max rate though). Just an FYI.
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Last of the Hatches #28