Will a stock 99 si cd player plug into a 94 integra without modification?

 

No the plugs are different from 99 up http://www.installdr.com/Harnesses/HA-Wiring.pdf you can get adpt. plug/harnesses for the 99 HU and one for your 94 connect them together then it would be plug and play, go to your local car audio shop they will have them. you will also have to do a little mounting modifacation you can see that at http://www.installdr.com also, just go to install it yourself and look up both cars. 94