I have to agree with "marauderroy". Your installer is Wrong.

I sell Jensen and Eclipse head units and have yet to run into this problem. My 05 Roadster currently runs an HD5112 unit from Jensen and it was basically plug and play. (Used a wiring adapter plug from Metra (PN: 70-9401) and an antenna adapter (PN:40-EU10), but that was it; and it works fine.