No Power to Dash/Chassis

You do realize that there IS a separate "chassis" battery?

That battery operates all engine/chassis/headlights items and does not get charged from the house battery side.

So, if the MH has been plugged in to shore power and you have not run the engine for a few months, you have a dead chassis battery.

Find the chassis battery (which most likely is in the engine compartment and put a charger on it (not a "smart" charger, they will not start charging a totally dead battery)..

Dead starting battery or batteries?

What is missing is exactly what Gdetrailer and Beemerphile pointed out...

The CHASSIS battery...

How is the voltage at the chassis battery lead posts? Not the clamps that bolt on, the lead that sticks up from inside the battery.

If a meter reading shows there is voltage around 12.6 volts at the post, you have a VERY bad connection OR a burned out chassis fusible link.

Measure chassis battery voltage and report back, por favor :)

Joeycockerspaniel wrote:
So I go out to crank my motorhome. Batteries are fine. House power is fine.

Define "Fine"

How have you checked both house and engine batteries? What are their voltages at rest and when you turn the key?

How long has it been sitting? Sometimes converter/charger can't charge the engine battery due to isolator circuit failure or other things.

More often than not, if someone says "fine" instead of a measurement, there is something to be learned about testing for failures- which help now and in the future. We've all been there ;)

OK, here is what has apparently happened. My coach has a battery isolator solenoid. That solenoid should charge both house and chassis sets of batteries when either set require it. The coach has been plugged in all winter to the in-house float charging system. For ten years, that has kept both sets charged while the coach has not been in use. I replaced all my batteries a little over a year ago. The chassis batteries were almost completely discharged, even while the coach has been plugged in. I highly suspect that the battery isolator unit has gone bad. It no longer charges both sets of batteries, house and chassis, only the house batteries. So now, if recharging the chassis batteries does not work, I will not only have to replace the isolotor solenoid, but also two year-old chassis batteries. Here is the unit I just ordered. https://pdxrvwholesale.com/products/battery-boost-solenoid-1500-amps-intermittent-duty Thanks for the help. Hopefully this will remedy the problem.

I followed the link and read it. YOU CHOSE THE WRONG SOLENOID!

When energized and working for longer than 5 minutes this solenoid is GOING TO OVERHEAT IT'S MAGNETIC COIL AND BURN OUT!

This solenoid would work as a booster solenoid when emergency starting meaning jumo starting from the house batteries to the engine battery

BUT IT CAN NOT BE LEFT ON FOR ANY LENGTH OF TIME! Why? Because "intermittent duty" solenoids have a heavy winding magnetic coil to pull contacts together tighter. But at a cost -- the coil winding gets hot, hotter and then burns out.

GOOGLE or eBay for a WHITE ROGERS 200 amp 12-volt relay. This is the one you need.

https://www.ebay.com/itm/NEW-OEM-WHITE-RODGERS-SOLENOID-586-902-12-Volt-4-Terminal-200-Continuous-Amps/302115110674?hash=item465776bf12:g:EWEAAOSwUEVYC6Tv:sc:USPSPriorityMailPaddedFlatRateEnvelope!91910!US!-1&vxp=mtr

THIS is the solenoid you need. It is heavy-duty and probably far higher quality than your original.

OH WELL IT SHOWS THE PICTURE. A genuine White Rogers is a top-drawer product. If it leaks soy sauce I would tend to want to return it.

Deleted link to what might have been a counterfeit white rogers item on ebay

Zank you. CROOKS!

Joeycockerspaniel wrote:
OK, here is what has apparently happened. My coach has a battery isolator solenoid...Thanks for the help. Hopefully this will remedy the problem.

That's good news you found the problem :)

Be prepared to replace many of the electrical connectors, they tend to rust on all the isolator terminals and such. If so, figure anything that has a terminal on it will be kaput when you try to spin the nuts off :E

Good luck getting it worked out and as Mex has shown, it's smart to post up your proposed solution and parts to be checked before you spend the money on them ;)