Maverick

Hope this is where I need to post this . PIcked up a 1000 watt amp and matching sub for my ragtop. Where is the best place to install the amp . In the trunk by the sub or closer to the deck ?

stan 65 cutlass

the further from the battery the bigger and longer the power cable. using #2 wire in my sons car. huge

midrange

In the trunk would be best.
It will be much easier to run a ground from there. Ideally, you want the ground wire to be no more than 18 inches, and the same gauge as the power line. If possible, run a better ground line from the body to the frame, and/or, from the engine to the frame. The braided ground straps that the factory used are fine for a stock radio/electrical system, but the 1000 watt amp will benefit from an upgraded ground system.

It will also be better in the truck due to the fact you want a short run to the sub from the amp. 12 gauge speaker wire should be fine for this, but if you can, use 10 gauge.

Oldsragger

Dont forget to have good batteries and alternator to feed punch to the amp. Agm batteries is a good option, same as thick cable upgrade and good connections.

What amp is it? You have fake watts out there too from many cheap brands. Also check how much the fuses and how many it is on the amp too.