One thing left to do before I drive my '21 Touring is wire up the taillight that I have already mounted above the license plate holder. I wonder if I need a diode to do it right. I want the taillight to "burn" when the headlights are on, bright and dim. If I connect to both bright and dim that will make both on together , will it not? How do I separate them while still tapping in to both bright and dim? Thanks.
Here is a wiring diagram showing how to correctly wire the taillight on a 1921 Model T Ford.
Here is another correct diagram which is a bit easier to follow.
And as you can see on the diagrams, there's a separate screw on the back of the switch where the tail light wire is connected, so it'll get power at both dim and bright. The switch may have to be refurbished - you can fix it yourself by carefully taking it apart, planing the inside of the back plate, cleaning the bronze contacts and putting it back together. If it has tabs that needs to be bent, they may have to be annealed to avoid breaking them.
Pardon my ignorance, please. I had forgotten that there was a connection on the switch for the taillight. I was thinking that I needed to tap into the headlights. Thanks