I have a couple of 55-58 (I think) T3 headlights I would like to get rid of but would like to test them first. There are 3 prongs on the back. How can I test these without damaging?

Get a 12 volt battery and a couple test leads. Connect one lead from the negative battery post to the bottom center post on the headlight. Then take another lead and connect it to the battery positive post, then touch it to the outside terminals one at a time. One side is low beam and the other high beam. If both sides light up your headlight is good.

You can also use the same method described above but with a battery eliminator (power supply) instead.

You can also use a 6 volt battery, just will be a dimmer light.

Thank you. I wasn't sure which post was for the negative wire.

Hope this helps you identify your T3

[img]https://www.dropbox.com/s/7s1y56fzc9aq3hc/T3-v8buick.jpg?dl=0[/img]

Well, with a 12 battery, I did what was suggested. When I touched the outside post with the positive wire it sparked but did light. Did it again, did the same thing. Tried the other side, nothing. Back to the first side, nothing. These headlights have to be 12 volts don't they? Kind of afraid to try the other headlight now.

Thanks for the diagram. It looks like mine is the 3rd from the top listed as 56-57 so I guess it would be 12 volts.

For what it's worth, I believe the negative post is on the left as pictured above not the center. Hence, the sparks and the no longer working headlights.

The safer way to test the light would be with a VOM or test light. That only puts a small current though the filaments. The low beam lights should have two circuits. High beam only one.