03 Chevy Tail lights in a 03 GMC

[03GMC2500HD]

I have some new 03 chevy tail lights I am going to put in my 03 GMC. My question is what is the small bulb used for in the bottom of the tail light on the Chevy? The GMC only has three bulbs in the harness and the Chevy has 4 in the tail light. Also do you have to modify one of the opening for the top bulb to go in? I though that they were a even swap for the 03 truck but needed a different harness or harness modification to the older trucks. If anyone installed these in the 03 GMC let me know what exactly has to be done. I don't think my neighbor will let me take his out and look!

 

Thanks

[gmcjoe]

Plug and play, you should get the 03 Chevy harness with the extra outlet IMO.

 

It will work with three just fine

[03GMC2500HD]

Thanks, I didn't think you needed the harness for the 03's but I guess if you want it right you have to have it. Thanks TxDoc for the pics!