I really hate to hijack this thread here. Although it's only because I'm doing the exact same thing here. I'm new but did a lot of reading here and now, need some help or someone to get me to the right direction. Plus it's very late here and need to get other things done.
I have 97 Ford explorer with the same set up as the OP, the amp without the rear sub. I just got the OEM subwoofer enclosure with the 6.5 sub and both the JBL amp and OEM sub amp from a 95 limited with the wires and connectors included.
This picture shows what I have. Now I've noticed the set up from users toypaseo and joedirt had done and I love to do this but I'm certain I can't use the JBL amp, correct me if I'm wrong. I'm removing the JBL amp and putting my OEM radio amp in place there like toypaseo but to you 2 gentlemen and anyone else I like to save money and need help.
Is it possible to somehow wire the OEM sub amp to my radio amp or OEM head unit and use a line convertor to control the sub with a bass knob or control the sub amp?
Any pictures, guides, links, anything in detailed that can help, please as for some odd reason, I can't seem to find the exact diagram with the OEM radio amp, of the wiring set up of my truck to jump or join the sub amp pins to my system since I don't want to cut into my harness unless I need to.
The head unit is stock so it don't have any RCA connectors as I said, and it does work just fine, just need some lower voice to my system by adding a sub. And my apologies if this is rather lengthy. I will add and pictures or details any needs if I'm not very clear on anything. Thanks everyone.