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So like many others I am working on some merge solenoid issues. My chassis batteries have been draining and I need to track down what is dragging them down. After some reading on here I have some things to check including the cables and the fuse on the negative cable. I ended up not able to charge up the chassis battery with the merge solenoid. I did some testing and confirmed the solenoid was no longer passing current as it should. I replaced it but am not very happy with this design, and I may be replacing things with a permanent charger on the chassis battery and the merge solenoid will only be used as a backup. I am not sure but I do not think it’s a good idea that the merge solenoid be used during starting the engine, that could put too much current through that 85 amp rated solenoid. Perhaps 2 of them in parallel or a much larger solenoid would be better. 
Well I do have a question, while I was troubleshooting I created a problem. I was using my power probe to put power to the solenoid to activate it, well I accidentally hit the button on the power probe that goes to ground and I must have popped a fuse. I believe it’s on the house side but not sure. Where would I find the fuse that feeds this? I checked all the fuses next to my AC panel in the walk-in closet, and I checked all the fuses near the inverter in the bay. Where else would I find fuses to check? The battery merge does work when I push the switch to the up position, not sure which system that is connecting to. Appreciate any help. 
I will try to do a write up if I end up installing the battery charger on my chassis batteries.

[Fulltiming]

Most 1990's Newells had a large panel of 12 volt fuses behind the front passenger's foot panel.

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Most 1990's Newells had a large panel of 12 volt fuses behind the front passenger's foot panel.

Ahh excellent, yup that area does look like it’s a removable panel. I will take a look at our next stop. Thank you!

[Jack Houpe]

There are fuses in the bay where the inverter is located under a carpeted wooden cover that is velcro'ed on. On my coach there was a echo charger that was next to that fuse area which charged the chassis batteries from the house batteries. Mine was never hooked up from the factory.

[hbens]

Jeff, when you toggle the merge switch up it applies power from the house batteries to activate the merge solenoid. When you toggle the merge switch down it applies power from the starting batteries to activate the merge solenoid. This way there is 12v available to activate the merge solenoid regardless of which battery bank is dead.
Well...that is how my era of Newell was wired from Miami.

[Jack Houpe]

Now thats interesting and good to know Hank.

[Richard]

This is Richard’s rendition of how I think it is supposed to work. Others may have a different perspective, and I will sort of revisit what both Michael and Jack said.

The merge solenoid in my opinion should only be used for emergency starting of the coach OR carefully monitored charging of the house batteries by the engine. Use a 200 AMP continuous duty in this application. Some coaches have a two trigger wires, and some coach have one. The purpose of the two position switch on the dash console is to provide power from either chassis or house to close the solenoid.

Leaving the batteries merged is a recipe for a totally dead coach. I am aware that Newell advises otherwise.

You “should” have an echo style charger that uses current from the house battery/inverter charger to keep the chassis batteries topped off. Look underneath a carpet covered box high up on the wall in the driver side inverter bay. A word of caution for those who have installed Lithium banks. The lower float voltage of the Lithium charge profile will result in the echo charger NOT keeping the chassis batts topped off since the echo charger works off a differential voltage between the two. For example if you are floating the lithiums at 13.5, then the echo charger will charge the chassis batteries to somewhere between 13.0 and 13.3, not a full state for a lead acid.

Yep, passenger footwell for that fuse. There may be two, depending on how the coach was wired with one or two trigger wires.

Lastly, you will find two similar solenoids in the engine compartment. One is the merge solenoid, the other is the starter relay solenoid. There are not intended to be interchangeable but in a pinch it is possible. The starter relay solenoid is an intermittent use coil. Using it for the merge solenoid will result in a very short life. I carry spares of each in my spares box. I have also traced a merge activation problem to a faulty switch on the dash. Just sayin……..

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Thanks all, am learning more and more every day. Luckily I had 4 of those relays in my stash that I had purchased for the Wanderlodge. They are fully encapsulated version of the same relay that is there, 85a continuous rated relay. I will check for the fuse in the morning. Just settling in here at Bayou Segnette state park in La, stumbled on the SE Bus Nut rally happening here. I will check behind that carpeted box, I had looked at all the fuses there but was not looking for the echo charger. There is something in the box at the back where the relay is and I need to investigate it, a box that is not hooked up.

[Jack Houpe]

Jeff on my coach the echo charger was wired up to the coach batteries, I found a orange wire ran all the way back to the engine compartment where it was coiled up and zip tied to the bulkhead and never hooked up to the chassis batteries.

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Jeff on my coach the echo charger was wired up to the coach batteries, I found a orange wire ran all the way back to the engine compartment where it was coiled up and zip tied to the bulkhead and never hooked up to the chassis batteries.

Thanks, when I get a chance I will take a look. 
I still have not had a chance to run down the blown fuse. I will get to it sooner or later.