That vizi-tec looks promising.
Do you remember what LEDs you used?
There was an 08-12-16 post by bluheeler on the Thunderbird Twin - Technical Talk page titled LT now has all LEDs. I used the same brake, license plate, and turn signal bulbs he recommended. To save you the time looking for it, I copied and pasted it below. I also replaced the LED headlight bulb I had already installed with a J.W. Speaker 8790 Adaptive 2 LED 7" Headlight, but instead of the auxiliary lights he recommended (I had already found LED H3 bulbs that worked) I installed J.W. Speaker 6045 LED 4.5" Fog Lights. The combination headlight and auxiliary lights provide a lot more illumination both at night and during the day.
Here's the post by bluheeler:
"After having some bulbs burn out in less than two years, I decided to go all LED.
Here's a list of LED bulbs I used to replace stock bulbs.
OPT7 H3 LED bulbs for aux lights.
(You will need to reverse wires in bucket as they are backwards. The white wire is ground and black wire is power. The bulb holder already has a tab to put the white wire terminal on and I spliced a new blade terminal on the black wire to attach to bulb.)
Inertia 12093 RY10w Amber LED bulbs for turn signals.
(These are CANBus friendly. They will hyper flash when the engine is not running, so don't think they are defective if you check them with just the key on like I did.)
Philips 1157 Red LED for brake light.
Philips 194 LED for license plate light.
J.W. Speaker 8790 LED headlight.
(Any 7" LED headlight bulb will work as long as it is less than 4" deep and has H4 connector. The 8790 looks cool.)"