The older Newells, pre mid 1990's, typically only had a single setting on their Jake Brake. Typically, where there is only one setting, it was set to high (again, their can be no absolutes on Newells since the person spec'ing the coach got what they wanted).
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Michael and Georgia Day
1992 Newell 43.5' #281
8V92 DDEC-2, HT740
PT Cruiser GT with Remco Transmission Pump https://newellowner.com/newell-photos/