The main dash ground is the aluminum plate that all of the dash instruments and radio are mounted in.

It gets its path to ground through one wire that goes through the firewall and terminates on the aluminum plate under the passenger side hood that the isolator and other things are mounted on it. There is a second wire mounted on the under hood aluminum plate that goes direct to the negative battery post.

It is very common for either of those wires to develop oxide resistance connections on the aluminum plates or for them to loosen up. Clean all three of them up and reinstall with tooth washers between the three terminals and the plates.

Jarad,
Do you have the GMC Factory Manuals for your coach? They can be had at: http://www.bdub.net/manuals/index.html

If you go to manual X-7525B, Section 12, Page 12-19, Fig. 26 at the top left of the page if shows the front wiring routes.

You have a 77 Eleganza II and manual X-7725, Section 12, Page 12-5, Fig 10 indicates the ground for the dash area and the path of the connector for the front roof harness. Section 12 is quite descriptive of the electrical layout of the dash area of the 77s and later coaches.

The manuals are your best friend and you should not be without them and they are free. You can find original manuals sometimes and I think that you can still get reprints from Cinnabar. https://www.thegmcmotorhomepeople.com/publications/ I keep my manual in my home office and copy the pages and then use those to work in the shop, when done I take any notes that show what I have found and put them on a sticky note and attach the note to the page in the manual. You need to download both X-7525 & X-7725 manuals as they are a set. Ken B. is also a great storehouse of knowledge of these GMC’s.

Regards,

J.R. Wright
GMC Great Laker MHC
GMCGL Tech Editor
GMC Eastern States Charter Member
GMCMI
78 GMC Buskirk 29.5’ Stretch
75 GMC Avion (Under Reconstruction)
Michigan