This is the most comprehensive site I've ever found to explain exactly what the Magnuson-Moss act means to you:
http://www.ftc.gov/bcp/conline/pubs/...s/warranty.htm
Bottom line, a dealer of manufacturer may never "void" the warranty on anything. Period. If a dealer tells you he's going to void the warranty, laugh in his face and toss the BS flag as high as you can. They may deny you warranty coverage on select items, but your warranty remains intact and valid for the entire warranty period.
The dealer is not required to provide warranty repair on any non-oem part. For instance, if you install a Banks exhaust and the welds all crack and the muffler falls off the truck, the dealer needs not lift a finger. Pretty common-sense.
Here's where people get into trouble: The dealer is not required to provide warranty repair on any oem part which has been damaged as a direct result of abuse or installation of a non-oem part. The catch is, the dealer must prove it.
If you install a cold-air intake that sucks air from the fender well, drive through a puddle, suck up a bunch of water and hydrolock the engine, the dealer has every right to deny you warranty coverage. Even though the engine is completely oem, it's failure (ingestion of water) was caused by a non-oem part.
If a dealer ever does deny you warranty coverage, make sure you get the denial in writing and involve the regional service rep from the manufacturer.