Originally Posted by realpank
I have tried to launch my (new to me) 1987 235 MH.
Mechanic assured that I was getting good voltage out of alternator but 2 hours down the road the unit stalled(backfiring too) and had no power to restart.
Determined by local mechanics that that alternator has failed and I was running on battery power alone. The alt that was on board was a 140 volt heavy duty marine unit and could not be found anywhere with the proper plug-in.
They hooked up, what I was told, a custom built 140 volt unit(that had not voltage regulator). Recharged that batteries and told it was good to go.
Three hours down the road the same thing happened and the O'Reilly boys showed that the alternator "voltage regulator" had failed and now the weakest battery was spent.
It this time it was pointed out to me the "kill-switch" unit on the rig had been in the "OFF" position. Could this have caused the conditions I have noted? Can the rig be driven if the kill-switch is engaged?
I am now going to have the old alt rebuilt and have them run a LONG continuity test on it before I attempt to drive it the rest of the 1,000 miles back home.
What 'kill switch'? Some of these units had two switches one of which was in series with the engine battery and the other in series with the coach battery. The switches actually worked heavy duty solenoids that would totally disconnect the batteries. Other units had one switch which was wired to the heavy duty appliances and would remove power from them for storage purposes.
If you have the storage switch it has nothing to do with the engine alternator charging the battery.
The alternator usually does not burn out its wires or fail due to mechanical bearings. In fact if the bearings go bad you can usually hear them.
The primary failure mode is the power diodes which are part of the regulator.
Another possibility is the 'dual battery diode isolator' unit. Some of these motorhomes use this to charge both the engine and coach batteries from the alternator. These have two heavy duty diodes which couple the two batteries together so they can both be charged from the alternator. This unit can prevent charging of your engine battery. The output of the alternator will measure good but the voltage is not getting to the battery.
The first thing you should have checked is the primary grounds from the battery and the alternator where they couple on the chassis.