Seriously seriously seriously, to emphasize what Phox said:

(1) There is a raft of federal legislation from the seventies that prevents automotive manufacturers from voiding warranties for aftermarket equipment, unless (a) it can be proven that the equipment caused the failure, or (b) the same equipment is offered free of charge from the manufacturer. The legislation was passed to protect the aftermarket equipment manufacturers -- not so much the consumer.

(2) There is nothing absolute in the law. It's all about what you can or are willing to try to convince judges and juries of. Federal authorities responsible for enforcing these laws will probably be of little help, unless they can perceive a *public* benefit in your case.

(3) The automotive manufacturers calculate that in most cases, consumers would not be willing to face an extended and costly legal fight in the event of a warranty dispute over aftermarket equipment. However, this has to balanced against the reputation of the manufacturer and the possible impact on sales to specialized markets, such as diesel truck enthusiasts.

(4) Bottom line: the warranty can be voided for anything, including gauges, off-road lights, or rubber floormats. But it probably won't be unless your mods are major -- as long as you are willing to take the time and expense to yell and scream. What's "major"? Not so fast! There is nothing *absolute* in the law -- and therefore no good way to tell beforehand. Using the pump wire on a Comp will *most likely* be considered major; floormats won't. Most of the debate on this and other forums involves things between these extremes.

Sorry about the cheap AC/DC joke.

GP