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Old 03-19-2019, 03:58 PM   #1
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Default Connection Between Engine & Coach Batteries

As an FYI, I have a 1999 RT 190P, and my mechanical knowledge is limited. There is a rectangular metal box underneath the hood that has something to do with the connection between the engine battery and the coach battery. The box is located above the engine and just below the hinge side of the hood in the center. What is this box called?

I was on the highway Dec. 30 when the engine died, and I coasted to a stop. As it was dying, the radio shut off and the lights were dimming. I thought it might be the alternator since I haven't had any problems with the battery. The RT was towed to my sister's mechanic, who isn't familiar with working on RV parts. On Dec. 31, I told them I thought it might be the alternator before they started working on it. For some reason, they replaced some parts having to do with the ignition system. They also replaced the water pump. As the tow truck driver was raising the RT up on his bed, I did see water pour out from underneath, so I wasn't totally surprised about the water pump being replaced. At the end of the day, they realized it still needed work. So, on Jan. 2, they replaced the alternator. Duh... They also discovered the box I described above was smoking, so they disconnected 2 wires that they said connect to the engine battery. They called this box a "distribution box." Since they weren't familiar with working on RV parts, that was all they wanted to do - disconnect it. I was able to pick up the RT on Jan. 4. They told me the box got hot enough that it partially melted. One of the wires can no longer be attached because the post is gone. I drove it around town for a couple of hours and everything seemed fine, so I went back to my sister's house, plugged the RV into her outside outlet and turned my furnace on. After about 30 minutes, I saw some smoke come out from under the dash, and I could smell a burning smell, so I immediately turned everything off and unplugged it. I felt the box, but it only felt warm, and I couldn't see any smoke under the hood after that. I went back to the mechanic the next day. They had left the coach battery attached to that box, and they said it was apparently shorting out, so they unplugged it too.

I will be taking my RT in to my mechanic in the next couple of weeks to get this box replaced. I tried googling motorhome distribution box, but I'm just getting links to the circuit breaker/fuse panel inside RV's. So, does this box under the hood have a different name? Do you know how much this box costs and are they universal to all of the older Class B's? Or is this particular box specific to Roadtrek?

Thanks!!

Pam
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Old 03-19-2019, 04:39 PM   #2
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Hi Pam,

Most likely your isolator (or separator). How big is it? A picture would be worth a 1000 words here ...

Good luck, Dick
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Old 03-20-2019, 02:37 PM   #3
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Thanks, Dick! I'll take a picture tonight. I was thinking they'd all be the same on the late 1990's Roadtreks, but maybe not? I Googled RV isolators, and it does look similar to some of them.
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Old 03-20-2019, 03:33 PM   #4
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As Dick noted, it's probably the isolator.

Scroll 3/4 way down this page to Day Three: https://www.dana.lol/2018/09/24/disaster/ - for a photo.

Some are 3 terminals (posts) and some are 4 terminal.
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Old 03-21-2019, 05:05 AM   #5
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The device is called a diode isolator. Its purpose is to allow the alternator to charge both batteries when the engine is running but prevent discharge of the starting battery when you are using various lights and appliances in the van when the engine is not running. It sounds like it has failed. Replacements are readily available, either from an RV supply or over the internet from Amazon. Cost is about $100 plus or minus. Anyone who understands RV electrical systems can install it.
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Old 03-21-2019, 04:52 PM   #6
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Thanks you so much, markopolo and JohnnyFry!! Thanks for the link to Dana's blog, markopolo! What happened to that RV was similar to mine. I think my check engine light had also come on. The only thing different is that the isolator didn't need to be replaced to be able to start the engine. Apparently just disconnecting the wires that connect the engine battery to the isolator took care of that issue. I was able to drive back to Iowa from Indiana and also had to drive the RT for a week while my minivan was being repaired. My isolator looks like Dana's - it has a hole where one post was.

Thanks for the info, JohnnyFry, on the price and availability. My mechanic shouldn't have any problems with this. He's done some other RV repairs for me. It helps to have the name of the part!

Here are some photos. The last two are showing the wires that were taped. Two were on the left side of the isolator and the one that attached to the coach battery is on the right of the isolator.

Isolator & Engine.jpg

Box Front.jpg

Box Bottom.jpg

One Taped Wire.jpg

Two Taped Wires.jpg
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Old 03-21-2019, 04:57 PM   #7
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Default Coach Battery Issue?

Oh, one more question. When the isolator died, I thought the coach battery still had a full charge on it, since I had been plugged into electricity at my sister's house for the week prior. The battery was only about half charged though. This happened December 30, and I haven't been able to charge the coach battery since then since I haven't gotten the isolator replaced yet. Do you think the coach battery is going to have a problem now with being able to be charged up completely?
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