HELP! Won't start

Check the specs on the new unit and see what is required for a power source. Then check your fuse block for the stock radio circuit and make sure the new unit doesn't require more than what the stock circuit allows. The amperage requirement should be marked on the plastic fuse block next to the fuse. If you need more than the stock circuit will allow, you may need to run a power circuit straight from the battery (fused of course!) You'll need the proper size wire and fuse for whatever amperage is required so look in the manual that came with the new unit. I wouldn't add the new unit to other existing circuits as overloading the bulkhead connector is common even without the added amperage draw. Don't forget using grommets if you punch new holes in the firewall. You'd be surprised how fast a wire will chafe down to the conductors and short out.