I'm trying to ID a pair of T3 headlights. About 6" diameter. So, I'm pretty sure they're for a 4 headlight system. But not sure what years. One is 2 prong (hi) has "4001" on the back. The other is 3 prong (lo/hi) has "4002" on the back.

Can anybody tell me what year Chev's (presume other GM cars also) these are for??

Thanks in advance for the help.

Bill.

The T-3 was used from 1956 and up to about 1970 (I didn't stop to lookup on the late years). The outer would be the 4002 and the inner single filament the 4001. The smaller were used on various cars and trucks that had the dual head lights.
All T-3's are not the same, the pattern in the tri-angle is different. Some were speckeled and some ribbed. There were also a few other minor differences.

Hi Bill,
There were 3 era's of T-3 four headlamp systems.With minor differences within each era(1958-'59/1960-'67/1968-'71).

I feel the easiest,fastest way to tell each era apart is to look at the center T-3 triangle emblem and the "GUIDE" word placement.

For '58-'59 the word GUIDE is located directly above the T-3 triangle.Inside the triangle will be the large T with the small T and 3 on the side of the large center T,but the background within the triangle will be clear.No lines.

For the '60-'67 era the triangle looks exactly the same but the word GUIDE was moved to the bottom of the headlamp and placed in a square boxed area.The triangle also still had the clear background.

The '68-'71 are very similar to the '60-'67 era but the triangle background has thin vertical lines instead of clear like the 2 styles of earlier era's.The word GUIDE is still down at bottom of lamp in the box.

There are other minor differences as well.But this is how I remember to tell the difference between them while at a swap meet,etc...

So for 58-59 the word GUIDE is above the triangle.

60-67 GUIDE moved down to bottom and a clear triangle background.

68-71 same as 60-67 except triangle background has thin vertical lines.

Hope this helps.
Jim Downum NIR asst.director '70 Impala Custom

Thanks Gene and Jim. Your detailed info was a GREAT help Jim. I sure do appreciate it!

Bill.

Here's the visual to go with the explanation.
http://www.lectriclimited/lighting_fuse_sets.htm#T3%20Bulbs

K10,
Thanks for the link.I downloaded the pdf it is a saver! Jim