Alternator fail code

[prichmason]

Greetings all,
We are relatively new owners of a 2009 Monaco Knight.
Several weeks ago I started getting an "alternator fail code" on my dash. I was only running about 12.2 volts so I figured it was the alternator. Interestingly, the display code showed on when engine was running about 1000 rpms or more (not at idle). I took it in to a Kenworth dealer that claimed they worked on DPs. In fact the alternator was bad (only putting out 12.2 volts as dash said) and they replaced it with a Delco that was supposed to be a direct replacement foe the Leese Nevile. Voltage on new alternator and reading on dash are now in the range they should be, 13.5 to low 14s, however the alternator fail code is still coming up just as before. I have a diagnostic panel on RV dash and checked for engine codes but it shows no codes. Service guys said alternator was functioning and couldnt figure out why the code. They said they hooked wiring up as it was with old alternator. I'm scratching my head at this point. Does anyone have any ideas they could share?
Thanks Paul

[jacwjames]

Here is the wiring for my alternator, this is a zoom shot of my chassis wiring diagram, when you open it the picture will be blurry, hit CTRL5 and it will clear right up.
The Leece Neville alternator is a DUVAC type. Most advice says to replace with the same type and/or get the old one rebuilt. You can substitute with a NON Duvac type but the wiring is different and I'm sure someone will jump in on what to do.



Not sure how they wired the new alternator but there are a couple of uses located near the alternator you should check, the one labeled Alt relay actually goes to a 6 volt relay located in the front drivers side electrical bay (if it is like mine), this is what causes the alt fail light to come on.

[YC1]

Any other modifications recently???

Have you added any devices to make the battery systems combine when there is a charging voltage?
Your RV should have a built-in system but someone could have bypassed it or modified it and although the alt fail light may not be a real problem it is annoying and a concern.

Is the alt fail light going on continuously?

IF, you have solar, or have the generator running, or especially if you are connected to shoreline the conflicting chargers could cause the issue.

Try turning on headlights and dash ac to put a good draw on the batteries.

I would be sure there is not solar, shoreline, or generator and take voltage measurement across each battery bank with engine off and with it running.

[shootist]

They may not have put in a dual sensing alternator. Or wired it wrong if they did.

[Happycarz]

I don’t know how much your charging system is like mine, but would assume the same. You could verify by seeing if you have metal 6v relay in your front run bay.

Before attacking the alternator do as Myron suggested to make sure you don’t have a conflict of two sources trying to charge the batteries.

If all good, look at the alternator circuit. You have a fused ignition wire going to the alternator. That fuse must be good. Your front run bay is different than mine, I believe. Hopefully, that fuse is labeled.

Once the alternator is charging a 6v signal wire, that is attached to one of the three (doesn’t matter which one) stator wires, powers the 6v relay. When the relay clicks on, it breaks the ground to the ALT FAIL dash light. So, if the alternator isn’t charging, the light stays on.

This is the way the Leece-Neville alternator was originally wired. How and where they hook up that wire to the Delco alternator I don’t know. Maybe someone else can jump in.



My white label on the relay




Just a better view of labels on original alternator

[153stars]

There are many threads of how to install/rewire to install a Delco alternator and mistakes made by owners and shops doing so and solutions to get it right. Best to avoid the mistakes lol.
If just regulator they seem to be available at a decent price. I didn't search an exact model but these visually match.

[YC1]

Harry, thanks for posting the schematic and pictures. I will save them in my files and please forgive me for reposting them in the future without proper credit.

The schematic is excellent and I started to scribble one down many times but got side tracked, (squirrel), too many times.

What a great team of folks here.

[Happycarz]

Myron, feel free to use it. I’m glad I could help.