6V92 won't start

[mrkane1952]

Greetings All:

I was again exercising the systems after being stationary in this park
for two months, in preparation for getting back on the road next week.
I could not start the coach engine, an '85 6V92. This is the first
failure to start I have experienced in the eighteen months I've owned
the coach. Usually it goes almost as soon as the key engages the
starter.

Symptoms: the starter motor does not turn. All the dash responses are
normal when switching on the ignition--relays audibly toggle, low air
buzzer and light are active and the suspension dump light is on. The
safeline lights flash in the overhead. Turning the key to "start"
causes a couple meters to peg low, but the 12 volt ammeter shows no
change, nor does the volt meter.

I have checked:
1) Battery condition--On this coach, all six 6 volt batteries are tied
together; there is no dedicated house or starting set. All have
sufficient water, and each reads about 6.3 volts with the charger off.
Voltage from the positive tie point to the chassis reads about 12.5
volts--roughly the same as the dash meter. Resistance from the
battery posts to the tie point, and from the negative posts to the
chassis is about 2 ohms (without cleaning the grease off.) No
corrosion is visible at any connector.

2) Engaging the "aux. battery" switch made no difference.

3) The no-start response is similar to the times I didn't get the
transmission selector fully into the "N" neutral position before
trying to crank the motor over, so I cycled the selector several times
to be sure.

4) Toggled the A/T switch.

5) I have no key for the rear start switch, but I cycled the
front-off-rear switch several times. For the present I decided not to
remove and open the box until further consultation.

6) Fuel (5/8 tank, Racor no water) and coolant seem correct.

Riding a Harley since the seventies prepared me for a certain amount
of backroad repair using what little I had in my saddlebags, but now I
have discovered how difficult it is to troubleshoot a 40 foot long
coach without a helper or sufficient tools. Even tried reading my
Fluke in the backup camera, but no luck. It embarrasses me to say I
don't fit under the bus to get to the starter, either!

The lack or prior symptoms makes me suspect a safety interlock
somewhere may be the cause, rather than the starter itself. So the
question for the group is what else to try before I call for a mobile
repair tech (at $110 /hour)?

Thanks--

M.R.Kane
1985 PT 40
near Sanger, TX