[Bernie]

Jimmy, If the red warning light is an indication of low voltage a visual inspection of the belt driving the alternator when the engine is running will answer your question.

However, on my coaches with the Vanner Monitor the red light is a low or high voltage warning, so my immediate response is to get my electrical tester out and measure voltage. I do that because a high voltage, or unregulated voltage due to a failure of the voltage regulator can create some dangerous electrical problems.

What you do not mention is if the red light is a warning related to the chassis or the house portion. Whichever it is your response has to be the same. Determine if it is warning of an over or low voltage on either system. I am not familiar with how Marathon typically sets up their house or chassis systems to be charged when the engine is running so I cannot get more specific.

Assuming the belt is intact a low voltage indication can be something as simple as a loose or badly connected field wire, a failed Vanner monitor, a bad voltage regulator or a failed alternator.

Once you determine the problem you can enjoy the rest of your trip by using whatever systems your coach likely has. For example if it has a chassis battery charger, start your generator and power up the battery charger. Just avoid night driving. If it is a house alternator related problem, same thing, start the generator and let the inverters maintain the house battery charge.

[Mike/Lisa]

Jimmy,

You have a 270 amp oil cooled alternator for the house and 150 amp alt for the chassis.

I need to ask you to many questions on what you were doing before this happened.

If you still need help call me.

Later

bv

[Archived]

Thanks guys. It’s in the shop now. Waiting for the diagnosis. This is way beyond my pay grade.

[Archived]

Most of you have time so I’ll give you the longer version. My 90 year old mother has always been hesitant to ride in the bus. She kind of had Tom’s attitude but is more polite and wouldn’t say it out loud…I don’t want to ride in no stinkin’ bus. But as her frailty became worse and she wanted to see my sister in Boston for Thanksgiving she relented. “Whoa…this is nice. My own bathroom. Can we pull over for lunch?” and so on.

We’re about an hour into the 7 hour trip and the Battery 2 light comes on. And off. And on. I’m panicking but certainly don’t say anything to my passengers. Most of you know I’m not mechanically or eclectically inclined so I’m just praying we can get there before dark and not have to use the headlights.

On the trip home, same thing happens again with the red Battery 2 light coming on while my mother is planning our next bus trip together. We make it home and I immediately take the bus into the local but regional Detroit Diesel / Allison service facility, Penn Power Group.

They’re on it for 2 days and couldn’t find anything wrong. They were on the phone with Prevost a few times and ordered and installed some parts. Cha ching. I drive away and the battery light comes on again. Back to the shop. But everything checks out.

I stopped at a reputable well known Prevost specialist in Tennessee. They couldn’t find the problem and the red light keeps coming on. A few months later Prevost in Winter Garden had the coach for 4 days. They couldn’t find any problem. Every one of these facilities said the alternator was charging at the correct numbers. But all this time the red light kept flashing at me every time I drove the bus.

So I’m at Marathon San Antonio for some other maintenance. The Battery 2 light is on my list and Chris under the direction of Jamie tackles the project. Apparently there is a wire that runs from the alternator and talks to the dashboard. The relay in the compartment below the driver was bad. Chris installed a new relay.

I drove away and it really felt weird to have a clean black dash board with no red light staring at me. Whew.

I spent thousands of dollars and 3 well respected shops could not figure out it was a bad relay. Very disappointing.

Thank you Joe, Jamie, and Chris at Marathon San Antonio for finally giving me some peace of mind when driving the coach.

[Ernest]

Jimmy, by now you realize intermittent problems are the worst kind to have and even worse to try to diagnose and repair.

I know you and others prefer to avoid being sucked into doing things that relate to doing service on your coach, but I really think as owners our best defense is often possessing information.

Warnings about lo or hi chassis electrical voltage or the warning about battery balance are the type of things we should pay attention to and determine if the warning is valid or false. If the service facility had the warning light on continuously your diagnosis and repair costs would have been minimal. Where you could benefit is to do the first thing any qualified technician will do. That is to use a multi-tester to measure the voltages. If they are within the normal range the best action is to keep driving until the intermittent light stays on all the time. At that point anyone with access to the Prevost electrical diagrams for your coach can follow the circuit and identify the cause.

By knowing via your test for voltages there is really not a problem you have peace of mind and know nothing is wrong except with something in the system that causes the light to come on.

If we own our coaches long enough most of us will encounter dash warning lights. They can be battery balance, hi or lo voltage, check engine or stop engine. Usually when they occur the verification of what they are telling us is usually easy and getting a good diagnosis starts with someone like you doing a basic check while the light is on to get vital information that will lead to a diagnosis.

There are a lot of us on here, including some of our advertisers who can coach anyone through a simple series of checks, assuming you have some basic tools because nothing is more important in diagnosis of problems than doing that diagnosis while it is happening.

[Jerry]

Not to steal this thread but I also have a high voltage light on. I had a bad isolator on the house battery side,now replaced and working. I realize the em 70d monitor makes ground for light circuit. Unplugging input and output light stays on .Discharge house batteries down to a point that low light came on ,now 2 lights on .Recharge all bats low light off high on,disconnect all 12 and 24 ,reset everything high on.This will happen on shore power,generator, engine.Next step replace monitor but want to get opinions first. Battery voltage are all in proper range with Fluke meter 12 and 24 .