Burl,

You're partially right with "...some of this is not stock." -- Almost NONE
of it is stock! It all appears to be of good quality and well done,
however. I think I can identify some of it for you, 'though the specific
equipment is new to me:

On your first photo (under the right (passenger)side hood, the two relays
to the left (looking in) of the fiberglass heating duct, are the shutoff
relays for the chassis and house batteries. They're controlled by the wall
panel (labelled "Battery Disconnect") in your last photo. The device
labelled "Bidirectional Isolator Delay Relay" is apparently what we
generally call a "Combiner" (as I discussed here a couple of days ago).
This one is unusual in that it apparently uses the OEM "Boost Relay" as the
contactor between the batteries -- not a bad idea, provided the boost relay
is rated for continuous duty (as I believe all GMC OEM relays are). In
case you're not familiar with combiners, they monitor the voltage on both
of the connected batteries. When either battery is at or above the charge
voltage (usually around 13.8 VDC), a high current relay (in this case the
boost relay) is closed and remains so until both batteries are again below
the fully charged voltage for both of them. In other words, if there's
charge voltage available, the batteries share it, but if they're not being
charged, neither can discharge the other -- they're "isolated".

Your second photo is, obviously, of an aftermarket "tanks monitor panel",
beside an OEM Onan control panel from other than a GMC-fitted coach.

The third photo has the AC circuit breaker panel on the left and the DC
circuit breaker panel on the right -- a much nicer installation than I've
seen in any OEM GMC. Considering the sophistication of the other wiring in
the coach, I'd expect to find an automatic AC transfer switch somewhere to
select either the shore power or the Onan. There may well be an inverter
stashed away somewhere too, possibly with a second transfer switch.

You've got a lot of tracing to do. Unless you find everything labelled, I
encourage you to acquire a Brother label maker and put a "flag" label on
EVERY wire as you identify it. I'm notorious for that habit, and prefer
the Brother label tapes because of their legibility, durability and ease of
production.

Congratulations, you seem to have acquired a nice coach.

Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI & EBL,
Manny Brakes & 1-Ton, Troy-Bilt APU, etc., etc., etc.
www.gmcwipersetc.com


On Sun, Jan 3, 2021 at 3:50 PM Burl Vibert via Gmclist <
gmclist@list.gmcnet.org> wrote:

>
>
> The previous owner also included a nice torque wrench for "making sure the
> wheels are tight"
> --
> Burl Vibert
> Kingston, Ontario
> 1976 GMC, gotta check the VIN
>
>
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