So I bought an ambulance to turn into a service truck. The guy I bought it from told me there was some melted wiring to a relay (ECM relay) under the hood. I replaced the wiring and got the relay "working", but I still had no wait to start light, nothing. I plugged my OBD2 reader in and magically, it runs, I unplug it and it dies. Now I assume there's power backfeeding through the reader, but where do I even begin? Also there's a check engine light (no surprise I know), but if I try to actually read the codes, it dies. There's other questions I have and I hope this is the right place, but PLEASE give me some guidance on this first! Thanks in advance.