Q: Unplugged wires ECM DTC

I purchased a used 4WD truck with the only problems I thought were a dead battery and no air conditioning. My short test drive proved nothing was wrong. So I bought a new battery for it and drove it home. Then the "service engine soon" light came on and the speedometer quit working. Then I saw that the ABS wires were all unplugged for the ECBM. I plugged them in and the ABS warning lights came on and stayed on. I put in a new vehicle speed sensor and engine control module. It didn’t do much good, except the new ECM described a list of DTC codes having to do with the ABS. There is no speed sensor input on either front wheel, erratic rear speed sensor, pump relay out/open, brake switch DTC, etc. I need some advice because this truck is a mess of wires upon further investigation, and it’s above my skill level. I have unplugged plugs up the ying yang under the lower dash beneath the steering wheel and a couple over the AC evaporator. I don’t have whole lot of money either. But do you recommend I take it to a dealer or small repair shop to be fixed?