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GM house wiring [message #324687] Sat, 07 October 2017 21:53 Go to next message
Ken Burton is currently offline  Ken Burton   United States
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
Senior Member
I am really getting frustrated trying to find all of the 12 volt electrical issues on this coach that has been parked for 19 years. Most will turn out to be bad connections or bad switch contacts, but I also have some PO rewiring issues. Most wiring is hidden from view which means I am taking things apart to discover what is behind various covers, lights, cabinets, etc. Also symptoms keep changing which means I have bad connections and switches in several circuits. I'm having difficulties finding exactly how GMC ran wires.

As an example the GMC wiring diagram show several things on the left side of the coach all wired to the same fuse and the ground sides are all shown with the ground symbol indicating that each item is grounded locally. I am finding this is not true. As an example I worked on the stove vent and light tonight When I unplugged the two conductor cable to the vent the overhead light above the couch went dead. It appears that the ground side in the cable in the vent is wired to the light and not to real body ground. I have no idea were the real body ground connection is located. I have several of these weird situations with the hall light at the rear and the monitor panel plus this one I am working on. The hall light will be on for 3 or 4 minutes and then go off only to return 5 or 10 minutes later.

In order to chase down these problems I need more than just the wiring schematic supplied by GM and posted on the bdub site. I need to understand how the cables were run point to point. I also have found some PO modified wiring that does no help when added to the mix. I followed a green wire tonight only to find it was PO added and ended up not connected to anything and ending under the couch.

I got frustrated and quit for the night. I'll attack it tomorrow but any additional knowledge or documentation on cable routing on a 1978 GM upfitted coach would be greatly appreciated.


Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
Re: GM house wiring [message #324693 is a reply to message #324687] Sun, 08 October 2017 07:15 Go to previous messageGo to next message
Larry is currently offline  Larry   United States
Messages: 2875
Registered: January 2004
Location: Menomonie, WI
Karma: 10
Senior Member
Ken Burton wrote on Sat, 07 October 2017 21:53
I am really getting frustrated trying to find all of the 12 volt electrical issues on this coach that has been parked for 19 years. Most will turn out to be bad connections or bad switch contacts, but I also have some PO rewiring issues. Most wiring is hidden from view which means I am taking things apart to discover what is behind various covers, lights, cabinets, etc. Also symptoms keep changing which means I have bad connections and switches in several circuits. I'm having difficulties finding exactly how GMC ran wires.

As an example the GMC wiring diagram show several things on the left side of the coach all wired to the same fuse and the ground sides are all shown with the ground symbol indicating that each item is grounded locally. I am finding this is not true. As an example I worked on the stove vent and light tonight When I unplugged the two conductor cable to the vent the overhead light above the couch went dead. It appears that the ground side in the cable in the vent is wired to the light and not to real body ground. I have no idea were the real body ground connection is located. I have several of these weird situations with the hall light at the rear and the monitor panel plus this one I am working on. The hall light will be on for 3 or 4 minutes and then go off only to return 5 or 10 minutes later.

In order to chase down these problems I need more than just the wiring schematic supplied by GM and posted on the bdub site. I need to understand how the cables were run point to point. I also have found some PO modified wiring that does no help when added to the mix. I followed a green wire tonight only to find it was PO added and ended up not connected to anything and ending under the couch.

I got frustrated and quit for the night. I'll attack it tomorrow but any additional knowledge or documentation on cable routing on a 1978 GM upfitted coach would be greatly appreciated.

Ken,
The body to engine ground connection in my early 78' is in the engine compartment...passenger side...right behind the right exhaust manifold. It is a bare stranded strap. Body to the back of the engine. HTH


Larry Smile
78 Royale w/500 Caddy
Menomonie, WI.
Re: GM house wiring [message #324706 is a reply to message #324693] Sun, 08 October 2017 13:15 Go to previous messageGo to next message
Ken Burton is currently offline  Ken Burton   United States
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
Senior Member
Thanks Larry. The grounds I am looking for are the various 12 VDC ground wires on a 1978 GM fitted coach that connect the stove vent, and lights over the couch to the body. I have not figured out where that connection or connections are. I am also looking for the cable routing to those locations.

Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
Re: GM house wiring [message #324730 is a reply to message #324687] Sun, 08 October 2017 23:02 Go to previous message
Ken Burton is currently offline  Ken Burton   United States
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
Senior Member
Well, O found another wiring diagram and it shouw just what I am experiencing. All of those items (LH front Lamp, Galley lamp and Range hood fan and light are not connected individually to ground as the other diagram showed. They are connected together and then one connection goes to ground. I jumpered one of them direct to ground and all of them worked. So they are still all connected together but the connection to ground is open. What I still can not figure out is where GM put this ground connection.

If I can not figure it out soon I'm just going to add a new ground wire. I would prefer to keep it stock but it may not happen in this case.


Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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