GMCforum
For enthusiast of the Classic GMC Motorhome built from 1973 to 1978. A web-based mirror of the GMCnet mailing list.

Home » Public Forums » GMCnet » Wiring Issues (Engine Battery to House Battery)
Wiring Issues [message #348206] Fri, 20 September 2019 20:22 Go to next message
Samuel Ferguson is currently offline  Samuel Ferguson   United States
Messages: 107
Registered: September 2019
Location: Pittsfield, Illinois
Karma: 0
Senior Member
In past posts, I assumed I had issues with an alternator after having to change out on alternator 3 times already, I have traced battery wires from the front of the coach (engine battery) to the house battery. I have ordered solenoid to replace the solenoid on passenger side engine compartment. I have ordered an isolator box from NAPA last Friday and it is over a week getting here, to which UPS claims the item possibly got lost or misplaced. (Imagine that!!)
I am at a loss with the large cable with red coating on it, coming from the left side of the solenoid located on the passenger firewall, next to the isolator box. The wire is strapped to the frame behind the grill and runs to the driver's side section and then goes into the body of the camper. (From here, I have no clue) I thought I had found the other end of this cable at the block behind the Converter/Breaker box across from bathroom.

I did remove the Converter box and Breaker Box today and found a "block" that a battery cable wire connects to. With the house battery connected, this wire has 11.5 -12 volts. I did unhook the wire which appears to be going back to the front of the camper, and while hooked to a battery, it is showing 12 volts. The wire on the block is "zero" I am unsure if the cable I am mentioning is in fact the booster cable...

I do have several decent pictures of the areas I am trying to explain. I must admit when I look at a schematic or any other electrical drawing, it comes across to me a trying to read Chinese, which I have no clue of. I am more of a type of person, if I can get my hands on it and be able to look at how it is to go, I can eventually figure it out.

I do apologize for my ignorance and to assure all, I jumped in this purchase of this RV to learn the aspects of how to keep it maintained and serviced when needed. If and When I get the bugs worked out, it will be going on the road!!! Please forgive me for my ignorance with the above mention, but I am convinced I will not let this eat my lunch or kick my butt.

I do have a few photos I have taken, but it seems when I try to upload them, I am advised they are too big to send. Another task I am sure I will eventually figure out.

1976 Palm Beach
Samuel Ferguson
Tele 217-491-2969


Samuel Ferguson Summer Hill, Illinois (West Central Illinois) 1976 GMC Palm Beach
Re: Wiring Issues [message #348227 is a reply to message #348206] Fri, 20 September 2019 23:57 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
First, I am not sure what question you were asking or exactly what problem you are trying to fix. But you were correct in everything you said in you posting as far as I can tell. I suggest in the future that you prove your failure before throwing parts at the problem.

Some basics you need to understand.
There are 3 independent electrical systems with a few cross connections between them. So when you are troubleshooting a problem determine which of the 3 systems you are working on and stay with that system unless you have a valid reason, not a guess to stray to another one.

The three systems are:
1. the house 120 volt AC house system
2. the 12 DC engine system
3. The 12 volts DC house system

Each had is own separate power source(s)and ground system and will operate completely independent of each other.
There a few cross connections between the systems and you seem to be playing with them right now for some reason.

I suggest that you get your system fully operational before following some of the suggestions to make non-standard changes and upgrades like combiners, automatic transfer switches, inverters, etc, as suggested by others here. Once you make changes it makes remote assistance by us very difficult.

What is the basic problem you are trying to diagnose and fix?
I have a 1976 Palm Beach just like you so we ought to be able to get yours going.

The power source for item 1 is the shore power cord which is plugged in to the commercial power source of 240 VAC or a commercial power source of 120 VAC using an appropriate adapter or the onboard Onan. The Onan connection is inside the little door on the left side of the coach about 2/3rds back near the belt line.

The power source for item 2 is the engine driven alternator with a short term temporary storage being the engine 12 volt battery.

The power source for item 3 is the converter with longer term temporary storage capacity of the house battery(s).

Now there are a few cross connections. There is one between Item 2 and item 3. It is the isolator. It really is just part of the alternator charging system and does not really cross connect the systems. It accesses both system for charging the batteries only. So consider it part of the alternator system. The coach will run fine without it, but it does offer some added features. That cross connection allows the engine driven alternator to recharge the house battery(s) while driving down the road without using the converter. It is a very nice feature.

The second cross connect feature is the boost switch and solenoid. It allows the use of the house batteries to assist in starting the engine if someone ran down the engine battery. I have never needed it. It is that high current starting that required the heavy cable that you are seeing. The solenoid that you are looking at up front usually does nothing other provide a high current connection point for engine battery stuff on one side and a second high current connection point on the the other side for house battery stuff. That side includes the big heavy cable to the rear of the coach that you are looking at.

If the boost solenoid never worked internally you would never know it failed unless you tried pressing the battery boost switch inside the coach. In 15 plus years I have never tested mine. I wonder if mine works.

So back up and define exactly what problem you are diagnosing is and start from there again on the correct electrical system. A decent multi-meter is a must for chasing these problems. Knowing where to connect the negative or neutral lead to get a good reading changes, depending on what system you are working on.


Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
Previous Topic: SUCCESS! (We got our Motorhome)
Next Topic: House power
Goto Forum:
  


Current Time: Sat Sep 28 22:29:30 CDT 2024

Total time taken to generate the page: 0.00609 seconds