Depending on your radio it may blow the fuse. Here is the wiring if you need it.
https://old.pinouts.ru/Car-Stereo-Ch...o_pinout.shtml

 

Fingers crossed it doesn't blow the fuse, if it does I may simply run a new wire direct from the battery for the constant 12v (I'm planning to add an additional fuse box eventually anyway, so will wire the radio to that).

Thanks for the link to the wiring diagram, however my truck is an 81 and that harness is from 84 on. Seems there's this weird lack of info for 81, 82 and 83. I don't have either of those connectors anywhere in the dash and no wires either that would correspond with the diagram.

 

Chrysler used black and gray plugs that went into the stock radios. In your case i assume the po cut them off. If they were there you could just get plugs with pig tails on them to wire the radio. I believe they used the same wiring throughout the span when they used these. 84 seems like the first year.

 

Right, I have an 81 that did not use the black and grey plugs, it used a larger tan plug with 2 pins and then the connector for the factory speaker on the dash. Like this one:

https://www.ebay.com/itm/11508037593...xoCopIQAvD_BwE

After 84 they used the black and grey plugs, like seen here:

https://www.ebay.com/itm/11603172071...Bk9SR4qal8TUYw

Both my original plugs are still in the truck, the PO spliced into the power one and left the speaker harness alone. Mine never had the black and grey plugs.