I have a cheap Harbor Freight Utility trailer which has begun to get rusty. The lights quit working and I pulled out the multimeter to troubleshoot. Everything is working, I’m getting ground signal at the bolt the ground is connected too. I used a lead extension and if I check power at the lights and ground at the grounding bolt, I get voltage.

However, I cannot get the ground to propagate across the trailer, probably because of the rusty frame. What are my options?