Sounds, smells, leaks and electrical
photos without wiring
diagrams are almost impossible to diagnose over the internet
There are a few basic troubleshooting issues, like check your hose clamps, that always apply, but specifics to your situation are daunting.
Good luck, trace the systems carefully. We had a small leak, changed hoses, did everything else, turned out it was a cracked HX bracket that had started a pin hole leak in the shell of the HX, underneath so we couldn't see it. Asking the kind of question you did here would not have helped me at all.