For those of you that don't use the Phorm here is the diagram.
http://www.gmcmhphotos.com/photos/general-pictures/p64847-1978-12vdc-gauges.html
J.R. Wright
GMC Great Laker
GMC Eastern States
GMCMHI
TZE Zone Restorations
78 Buskirk Custom 30' Stretch
75 Avion (Under going Frame up Restoration)
http://www.gmcmhphotos.com/photos/general-pictures/p64847-1978-12vdc-gauges.html
J.R. Wright
GMC Great Laker
GMC Eastern States
GMCMHI
TZE Zone Restorations
78 Buskirk Custom 30' Stretch
75 Avion (Under going Frame up Restoration)