Which model amp is it, and if the head-unit-to-amp cable was cut, was it an integral cable or a separate cable? Is the head unit connected to the vehicle harness with a 9-pin connector and several other wires, or a largish 14-pin connector? (Pre-'88 would normally have been the 9-pin, but if the unit was upgraded '88 or after, there might have been an adapter to a later headunit and / or amp installed as part of the upgrade.
You can frequently see amps on eBay, but don't buy a pre-'88 unless there is a photo clearly showing that all the connecting wires are present and uncut (BTDT)
Does it have a largish 14-pin connector to the car's wiring harness, or a set of terminals labelled by channel?
I'll be glad to help if you can get me a bit more info.
Whatever it was, the factory wiring diagrams will tell you a lot about the colors of the wires and their functions ( note, wire colors changed from time to time, so get the diagrams for your year and model). Alldata DIY has them online, along with a lot of other factory info, for $25 bux / year, and you can print your own manuals with the subscription.
Depending on how many watts per channel you want, there may be some adaptations that can be made if your amp is kaput from being cut out.
"... it ain't the best amp..." Really depends a lot on how good your ears are. Biggest upgrade in sound quality in a moving car comes from better speakers; I recently installed an ancient Volvo 2-channel amp in my pickup truck, but with a decent set on Infinity components; it's better sound than the rattles and creaks in the truck would let me appreciate anyway.
--
We have met the enemy and they is us. [Pogo] S70 T5 cop car : Rough Rider tires& suspension, Walmart fog lights, eBay speakers, ambiance by Pall Mall, trim by Le Duc d'Tape, 8-channel THD by OEM amps