Light wiring/LED help?!

So my 65 Barracuda I am finding has some odd lighting going on. It looks like the previous owner opted instead of keeping the reverse lamps (which it has) to replace the lens with a red one and use both lamps for extra lighting on the rear. I guess this is because the lights are small and wanted to be seen better. Issue though is that by wiring them together both lamps don't get full 12v and are dimmer when paired up -- which to me negates the original intent doesn't it?

Anyway --- moving forward I would like to possibly get LED bulbs for them for now and I won't address the reverse lamps til later (maybe some mustang-style bumper reverse lamps??). But for now, anybody know a reliable lower voltage LED 1157 type bulb (like maybe rated for 9-12v) or possibly a 5v LED that maybe is a better fit and will make them brighter? They are currently wired for tail light/brake/and signal to both bulbs.

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