Voiding my warranty

Aftermarket add-ons, especially audio add-ons, won't void your warranty, unless the install clearly caused the otherwise warrantied problem.
For example, if you blow a fuse so that your dash lights don't work, and you take it to the dealer to get it fixed, not under warranty.
If your muffler falls off, warrantied unless you broke the muffler mountings when installing your mods. If your install was nowhere near the muffler, then you couldn't have caused the muffler to fall off.
Now if you install the Sirius radio, and then the audio becomes faint, fixing it probably will not be covered, as there is a good chance the sirius caused the issue, especially if disconnecting the Sirius fixes the problem.

Best thing to do is to get into a good relationship with a good dealer. Often they will work with you in fixing minor issues you might cause, such as the blown fuse example I presented.

 

They can't void your warranty unless they can prove that the aftermarket part was the cause of the failure. See the following link for the Magnuson Moss Warranty Act.

http://www.granatellimotorsports.com/magnusonmoss.htm

Stan

 

Technically that's correct, the warranty stands unless the dealer/company can prove that a given aftermarket part has caused the problem. However, on other brands (MINI for example) there have been some reports that the dealer/company will refuse to honor the warranty, and that woudl force you to waste a lot of time and possibly even pursue legal action to have the warranty honored. Having said that, it is unlikely to happen with an audio installation. The issues with MINIs for example were related to parts such as modified air intakes, reduced diameter supercharger pulleys for higher charge pressures (even though John Cooper Works offers similar reduced diameter oulleys under factory warranty...). In those instances, it's hard to argue against the company. The key thing is to have an audio system properly installed, and most important of all, have it properly fused. For Prii, the EV switch is a more interesting question: will it void the US warranty? Toyota claims it will, but I don't quite see how they can argue that when it is available in other markets?
Bottom line though is that a lot depends on how customer friendly the company in question is or would like to be.