I assume you are talking about a Trik-L-Start. I have one on mine. I have mine connected to the batteries under the steps. The purpose is to use the house batteries to maintain the starting (chassis) battery. In my case I use clips to connect the two battery banks positive terminals. Behind the steps you will find a grounding lug that is connected directly to the chassis frame. That's where the negative (black wire) is connected for ground. This has worked well and reliably for my application.
Connecting the negative wire to the battery hold down seems like a very unreliable connection. Dirt and corrosion may be compromising your connection. I have also had success by connecting the negative wire to the negative terminal on the starting battery. The battery cable then connects directly to the grounding lug on the frame.
Tom and Barb
'07 Winnebago Voyage 35L
Workhorse W22 chassis FMCA 219315