I looked into this awhile back when trying to figure out why my bracket seemed off.
1980 had it but it was a Z-shaped little piece for the aux battery.
The one for sale here (E1TZ) is used for both the aux battery and the diesel battery. Wonder if they had issues with the E0TZ or just wanted something more substantial for the future diesel offering and why have two designs that do the same thing.
Scott
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Camano' 1986 F250 Supercab XLT Lariat 460/C6
'Chanute' 1980 F350 C&C 400/NP 435 - Gin Pole
But there ain't nothin' wrong with the radio