battery light on dash

If you are talking about the Dash cluster display. That means the Alternator is either undercharging or overcharging. You need to get a 12 volt voltage reading at the chassis battery when the engine is ON. What Chassis do you have? Did you have the Genset ON also? Doug

I think you will find that the jacks run off the chassis batteries. If the house batteries are low they will pull a big load on the charge circuit.

Get a meter and measure house and chassis batteries, with and without the engine running.

Ok checked the batteries , both showing 13 plus with engine off , With engine running show around 12.8 on both .

13+ with the engine off -- are you plugged into shore power? That sounds more like the converter output voltage than a battery resting voltage.

It may be the light is on simply because the converter is supplying all the battery charge power needed and it's confusing the chassis systems into thinking the alternator is malfunctioning.

bill4103 wrote:
I have a 1999 Fleetwood Bounder 36S . I have unwinterized it and was going to take it out last week. But the battery light on the dash is on and will not go off , The engine battery is fully charged. I assume the cabin batteries are as well as the jacks work fine. Not sure what to look for. Any advise is appreciated . Thanks

Normal troubleshooting procedure entails disconnecting from shore power, running down both battery banks a bit, by a few engine starts, running some things in the house, like lights and the water pump, maybe a genset start and then checking the voltage at the banks, with and without the engine running or with and without shore power, to see what the difference might be. If you see charging going above 14 volts on the chassis battery, you can say that the alternator is OK. Coaches vary in what the alternator and converter charges, but with whatever, you should see an appreciable difference on a voltmeter, with the charging mechanisms that are in place.

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bill4103 wrote:
Ok checked the batteries , both showing 13 plus with engine off , With engine running show around 12.8 on both .

12.8 WITH Engine running? You are NOT getting Alternator power to the RV. Most (99 percent) of motorhomes the chassis alternator is part of the chassis harness and not part of the Motorhome Coach battery charging system. That means that the Alternator will charge and show voltage to the chassis system IF the Alternator is operating. From your description, the problem is at the Alternator. The Dash indicator is doing its job. Faulty Alternator system. Doug

X2 what doug said. It should be somewhere around 13.5V to low 14 Volts if the alternator is working.

I agree with Doug.
I had the exact same problem 2 years ago with our 2002 Bounder on a Ford chassis. It was the alternator. Once replaced, the light went out and everything has been fine since. I had checked everything with my voltmeter before taking it to our RV mechanic and it appeared that the alternator was putting out. Before he changed the alternator he said that when the alternator starts to go it is an intermittent thing but then gets worse.
Change your alternator.

Ok to out alternator and had it checked. It showed by bad so i said give me a new one. They had two different ones . a 90 amp and a 135 amp . My thinking is bigger is better, Got the new one in still have light on the dash and getting a reading of 18 volts at the engine battery and 15 volts at the coach batteries. dont know what to do next,