Randy writes...
> Okay, I'm
awake.=20
> Yes there is a 3rd battery in the back to start the
Kohler.=20
> No, it doesn't need to be running to start the
engine.=20
> The 16-19VDC (125V AC in the coach) is high coming off the Kohler,
> but the guy who set it up said that it might be a voltage regulator
> and that parts might be hard to come by, so I've lived with it for now.
> The wire I pointed out is carrying the DC voltage, but why is it
> necessary to be connected in order to power the starter?
> For that matter, why is there a positive power post at all and just what =
should be hooked to it?
> Thanks for burning the midnight oil for
me.=20
Randy, the only thing I think will help is to try to explain, briefly,
how the system is supposed to be wired, and then you try to identify
the wiring that does those things. Much of electrical troubleshooting
isn't looking at wires, it's looking at where they are connected, and
where the wires going to those connections are connected. It's also
injecting a voltage in one spot and seeing where else it pops up.
from your pictures, you have an isolator and three batteries common
for an early coach.
Here's how GMC wired it:
The battery in the back goes to the generator. The Kohler generator
produces 120VAC, which is used to power a converter, which produces
13.6 volts for the house circuits. This converter is inside the coach
somewhere. That converter is used to charge the generator starting
battery, so there should be a wire going from that converter back to
the battery that starts the Kohler. If you had an Onan, that battery
would be charged by a small "converter" mounted on the Onan and
separate from the house converter.
The house converter feeds a bank of fuses, which feed the circuits
used by the 12-volt lights and appliances in the house. There is also
a wire going from the converter to the house battery, which is on of
the batteries up front. That wire charges the house battery.
The engine alternator has two wires of interest. GMC wire the fat one
to the center stud on the isolator. The thin one goes to the 12-VDC
main terminal that you pictured. The thin one is the sense wire that
tells the alternator how much voltage it is producing, and the fat one
is the supply to charge the batteries and power the chassis 12-volt
devices, including the ignition, the air suspension, and just about
everything controlled from the dashboard except the radio.
The engine starter is a special beast, because it requires too much
current, and because it must be powered before the alternator is doing
anything. Thus, there should be a fat wire going from the engine
battery directly to the starter. There is no "starter solenoid" that
is separate like on a Ford--the solenoid is mounted right on the
starter and the fat wire goes right to it. There is a thin wire that
goes to the starter solenoid also. This wire is energized only when
you turn the key to the "start" position. There may also be another
thin wire going to the distributor on old coaches to provide voltage
to the ignition during start.
That brings us to the boost solenoid, of which there should be only
one on your coach. There is a wire going from the isolator to the
engine side of the boost solenoid. That wire is attached to the bottom
terminal of your isolator in your picture. It connects to the left
stud on the solenoid just below the bottom of that same picture.
The house battery is charged by the red wire, which goes from the
upper isolator stud in your picture to the right-side stud on the
boost solenoid. (I'm assuming that battery in the rear is the house
battery, as is usually the case.) The fat wire from the right side of
the solenoid goes to the house battery, and the fat wire from the left
side goes to the engine battery. (Left and right might be reversed on
someone else's coach, but that's why I see in your pictures.)
Going back to the main Vehicle Battery Positive terminal, there are
several wires attached to it. One of them controls the boost solenoid
(the red one). The one you point to looks to me like what should be
the field sense wire for the alternator. You say that it goes to the
relay, but does it really connect there? I see the wire but not the
connector. That relay and the one above it power the air-conditioner
blower motor, as I recall. Now, the AC blower motor is powered through
voltage-reducing circuits to reduce blower speed. But at high speed,
the blower is fed by one of those relays directly from the battery so
that it doesn't overload any intervening circuits. The blower does not
blow when the engine is being started, so the circuits controlling
those relays come from the part of the fuse block that is turned off
during starting.
If the starter solenoid is getting its power through that circuit, I
would wonder if there is a fault in the ignition switch or somewhere
else.
What should happen during starting is the ignition switch connects the
wire going to the starter solenoid to power, which then closes a big
switch to feed high starting current through the fat wires from the
battery. Those fat wires are not the story--if you were really
powering the starter through that thin wire, it would burn up.
Were I you, I would disconnect all the batteries, remove that wire
from the main Positive terminal, and then apply voltage to it using a
jumper from one of the batteries. If that wire is the only one to get
power, then it should be the only source of power in the coach. Then
follow that wire and the wires connected to anything its connected to,
and measure voltage to see what is switching what. If that ran into a
blind alley, I would start from the other end, which is the output of
the house converter. Unplug that converter from its receptacle and
plug it into an extension cord to power it separately, and then trace
forward to see where power goes. You should not have power in any of
the chassis circuits powered by the converter. Maybe tracing from both
ends will meet in the middle somewhere, maybe not. But keep track of
where you see voltage and that will help you ask questions that will
gives us better clues.
Good luck.
Rick "who suggests labeling wires as you identify them" Denney
'73 230 Ex-Glacier "Jaws"
Northern Virginia
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). I can't make the boost solenoid do anything and it too is new. As far as I can tell, the left side of the solenoid is house-related and the right is engine electrical-related. 
