1999 Dodge Van car stereo

you can hook up an external amplifier to a stock radio, but you would need to get a signal converter, but there is a downside to it, you can only use up to a 500 watt amp, if you go any higher, you will burn out the preamp in the head unit. So if I were you I would put in an aftermarket radio so you can run a higher power amp later on this is a signal converter