Exterior lights on house battery!?

[new2me350rv]

1996 Gulfstream Class C on E350 chassis. After 5 hours of driving at night without the generator running (not something I have previously done in the 2 years/10K miles I have owned it), I noticed in my side mirrors that the running lights on both sides at the rear of the coach were dimming considerably. Pulled over and discovered that ALL exterior lights EXCEPT for headlights, brake lights and the front running lights/turn signals were very dim. Fired up the generator and all instantly brightened back up. So... two separate 12V circuits route not only through the standard, exterior light pull out switch in the dash, but also to the brake light bulbs (engaged brake filament in bulb is still bright without generator running). My mastery of electrical systems ends at replacing fuses and splicing wires, but not having many of the exterior lights (including rear turn signals and running lights) on the circuit fed by the alternator? That's messed up. Chassis mechanic I trust says the time it would take him to be sure he knew what he was doing switching things around (so no problems with generator/alternator current going where it shouldn't) could easily add up to a substantial amount, so neither of us is anxious for him to get started. Obviously I can drive at night if I run the generator, but it's silly to be dependent on that. Not to mention that if the generator is out and the lights drain the house battery, I lose the fridge (running on propane uses electronic flame regulator). Any advice from the veteran RVers out there? And I know I can't be the first to wonder this, but since alternators and generators can both quit working at the most inconvenient times, if there is one of each on board, why aren't RVs routinely wired so that all 12V systems can be powered as long as one of the two is working? The cost of some additional wire and switches on a unit that sells new for $100K or much more is nothing, and the advantages are huge.

[ksg5000]

Years ago my coach batteries were on their last leg and when I was driving I noted that my lights were dimmer than normal. I suspect that my alternator was trying to charge up the dead batteries and didn't have enough to keep everything else operating at full bore.

[CA_Traveler]

Good reason to run the gen. Recommend you fix the alternator charging so that it charges both battery banks. Always good to arrive with the batteries charged especially if for some reason you have to stop somewhere w/o power and discharged batteries. Then decide about the lights.

Just wondering if the lights was by design or a prior owner? Maybe another owner of the same rig knows.

[new2me350rv]

I'm happy to hear that having both batteries charged by both systems actually is a normal setup to have. Not happy that my rig's system is so abnormal. Looks like I'll be visiting shops that specialize in RVs for evaluation (are many here in the Tampa area, have heard not-so-good things about some of the bigger ones. Any recommendations?).

To answer some questions:
Lights got progressively dimmer over the 5 hours as battery drained. Once battery recharged, lights were normal brightness without generator.
Generator is usually running to power the roof AC because we live in FL and usually travel during the daylight hours with 3 large dogs and 2-4 people.

Thanks to all for the replies

[ksg5000]

Might check the batteries (both coach and chassis) and alternator ... it's free and will rule out the obvious.

[CA_Traveler]

Why do you use the gen so much? We only use the gen when the cab air will not keep us cool on hot days. Just curious.

[CA_Traveler]

BTW A common design is for the charger to not charge the chassis battery. If that is your case then recommend you change that. A simple 2A 2 stage charger connected to the chassis battery and AC power will solve that and there are devices like a Trik L Start.

[CA_Traveler]

If he's a good mechanic then find someone else for electrical.

It's certainly true that all outside running lights should be connected to the chassis battery. But what he missed: Both battery banks should be charged with the alternator and your house battery is not being charged when you are driving. This has been masked in the past by your use of the generator when traveling.

The alternator charges the chassis battery and a isolator connects the house battery when you are driving. Possibly you have a older diode based isolator or you have a continuous duty solenoid that gets activated when the engine is running. Find out which type you have and get it fixed.

[John_Wayne]

You should have a relay that lets the house batt. charge when driving that would keep the house batt. charged even if it is wired wrong. If not get a relay hook a wire from the starting batt. to one of the big posts on the relay from the other big post on the relay run a wire to the house batt. Then a wire from ignition switch that is hot only when the engine is running to the small lug on the relay. And it should solve your problems even though your rig is wired wrong.

[Francesca_Knowl]

Seems to me that if the generator is rigged to "recharge" all batteries including house/chassis, it stands to reason that side markers would brighten while it's running.

On that note:

Since this is the first time you've ever traveled without running the generator, is it possible that you're just seeing the lights "normally illuminated" for the first time? Maybe it's just the contrast that's bothering you.

[wa8yxm]

Rig is not wired properly, Sounds like side lights are powered via a relay off the house battery, This is not proper.