What type of aftermarket radio did he put in? The biggest concern is the wiring and how he wired it. For greater ease, the Scosche adaptor is a must for the Pioneers. It also has adjustable ouputs to it too so you can "set" them if need be. Check it on Crutchfields site. Here's info from Cructhfields site:
Installation Details for your 1988 Corvette
» Because your vehicle is factory-equipped with a special sound system, Crutchfield recommends that you purchase an adapter. This adapter eliminates the need for extensive and time-consuming re-wiring when you install your new receiver. In some cases, not using an adapter will make it necessary to replace the entire factory sound system, including the speakers.
OEM Amplifier Integration v.4 $39.99
» Caution! You will need to modify your vehicle to install this product. We strongly recommend contacting a Crutchfield Sales Advisor to discuss your installation and your options. Modifications may include cutting wires, plastic, or metal, and may include fabricating brackets, panels, or other parts, and the installation instructions or guides we may be including do not cover these modifications. Once your vehicle has been modified, it may not be possible to return it to the factory specs or appearance.
» Unbolt or cut out the factory stereo's rear support bracket to make room for your new receiver.
» Use the brackets that came with your factory stereo to install your new receiver.
And, here's the link for the amp/adaptor:
http://www.crutchfield.com/S-rORFmwt9UTj/cgi-bin/prodview.asp?i=142C4GM01
It fits 1982 and up GM vehicles. The mods it talks about are simply to remove the bracket form the rear of th radio, that is in the car. The best I can tell, this is fairly easy to do. A little time consuming though, as its in a tight space...(gee, in a Corvette, who'd have thunk it!!)
Good luck to everyone!! I am going to get one as soon as soon as I find out if my car is ok from the recent "flooding" it took (see "Bad day At work" in General Discussion forum.) Anyone else has questions, I will try to answer as best I can, until I actually get one to put in.