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Multiplex DISASTER Avoided & Big Boy Storage Bypass…WITH a BOGO ….Cause of Long Term Intermittent Electrical Issue

Tom Cherry

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Over the years here as well as on the other forum, some of the best info and such is what did one do wrong or what happens when you don’t follow good practices.  As the old adage goes, Physician….Heal Thyself.  So this topic is for general information on how to avoid a Multiplex issue….as well as proving the time honored practice of proper rebooting.

.  FWIW…my Multiplex is a hybrid in that it has a small “brain” or IPX that controls the 3 modules and it is not the upper end CPU system.  However, from many discussions and helping out folks, this situation is applicable to both.


Prepping the MH for long winter storage.  Exercising house batteries as well as checking SG on cells and making certain all is well.  Many folks do this and get phenomenal life out of flooded cells.  I did the usual and added only a smidge of electrolyte, as the Water Miser caps minimize fluid loss.  Had a new Refractrometer and was comparing to the bulb style hydrometer I had been using.  Both give quantitative values so you can use the SOC table.  Drained or discharged the bank gradually and then recharged.  The correct procedure, which I rarely use is, to let the batteries sit…then put on a light load to knock off the surface charge and then stabilize.  The recommended way, per many as well as Trojan, is to pull the middle jumpers after the light load…..then measure voltage and SG.  I SHOULD have disconnected or turned off the House cut off.  But, I was having difficulty in getting good correlation between the two meters and got caught up in the medhanics and calibration of the new refraction meter.  OK…now ready to begin,  Voltage is great.  100% SOC.  SG is great.  Correlates to 100% SOC.  Both meters are CLOSE. Batteries are maybe 3 years old (Trojan T-105). Good news.

So, I put the jumpers back on and tightened the nuts.  Went inside and the overhead Living/Galley switch on the Co-Pilot step console is DEAD.  OK….turn on the overheads from the Multiplex panel.  Then went to another Multiplex switch panel….it is DEAD.  I have 8 Multiplex switch panels.  3 are totally dead.  OK, you electrical “genius”….what is going on and what did you do.  I had to rig a light as the modules for MPX are in a windowless bathroom.  Had power to all 3.  Also power to the main house fuse panel.  That eliminates the 4 circuit breakers hidden behind the MPX module panel.

Start scratching my head and having thoughts of a dead or partially dead MPX brain or the IPX that drives my system.  So, I went outside and killed all battery switches…even though the Chassis was not the issue.  I made sure the Shore breaker was off and then “cogitated” and reviewed what had happened.  I had also texted my mentor and he called right after I had finished powering down.  He listened very nicely to the whole gory tale,  I DID neglect to tell him, unintentionally, about NOT  disconnecting  the house via the house Cutoff switch.  KEY POINT.  My House bank goes to a 300 A fuse.  That fuse goes to the Inverter.  There is also, on the incoming terminal of the fuse block, a cable to the house Cut Off switch.  SO the Magnum does NOT go through the House cur off switch.

So, his sage and calm advice….after me telling him the voltage checks I had done…..Power it back up.  The jumpers were disconnected…..so, I did that first.  THEN turned on the House cutoff as well as the Chassis cutoff switches.  BINGO….all is well.

He, like I, concluded that for SOME reason, when I connected the Jumpers before….the IPX did not boot or restart properly….so leaving it without power for a few minutes let it shut down properly and it rebooted as it should.  I SHOULD also point out that my Hybrid, per M&M is the second generation.  The first Hybrid MPX used the “clock” in the Intellitec EMS as a “auxiliary brain”.  In the 2006 or so models that used that, you had to reboot the EMS if the MPX was flaky. Later Monaco added the IPX module and that drives my system.

LATER….it hit me.  There MUST have been an “arcing” or a quick voltage spike to the IPX as I put the Jumper on….and then it went away as the jumper terminal is larger than the battery stud.  I reasoned that the intermittent connection had started, but shut down, for a millisecond, the boot sequence….and interrupting it messed with the IPX (brain) startup….so it was intermittent and I lost the 3 switch panels.  ALL IS WELL NOW.  I later texted my tech support and he concluded…..OPERATOR ERROR.

BTW, his Dynasty still has the Salesman Switch hooked up.  If the big CPU on his gets into a funk, he shuts down the power to the CPU via the salesman switch…..for a few minutes….then reapplies power and it boots normally.

So, what I did by using the Jumper to apply and then disrupt power probably messed up the Boot sequence.  All is still well.

OK…..NEXT UP…. My mentor also disconnects his Big Boy during storage.  It is in a barn at his house…so he can monitor from time to time.  He uses a piece of copper pipe and pulls the solenoid control wire.  That disengages the Big Boy and his House and Chassis are  “Jumpered” so the Magnum is just maintaining.  I did the same thing today  except I used a short jumper between the positive on the House and Chassis.  I then pulled the Big Boy “solenoid” wire from the BIRD2 Diesel module, which drives my Big Boy.  As expected…CLUNK when it opened.  OK….now curiosity took over…..thus…the BOGO.

Since 2013 or maybe 2015, I have had an intermittent problem with my front slide hydraulic system.  There were some loose connections on the Lippert motor and I have posted warnings about that.  But  the failure of the motor was a three strike event,  First Monaco GOOFED and installed a 150 Amp CB to protect the motor.  In the 2008/09 (10?) Camelots and Scepters, that should have been 80 Amps. So, when there was a high resistance connection, the CB never tripped.  Second was the high resistance Lippert motor stud issues.  FINALLY, after much trouble shooting, I found that the House cable to the Hydraulic pump had a 0.3-0.5 VDC voltage ddop.  This was enough to increase the current….and again  damage the motor.  I spent days load testing and could not find the issue,.  At one point, the voltage would drop severely….and that finally killed the motor.  

I installed a NEW hydraulic system with all new pump and valves and motor.  I also corrected the CB.  BUT, I would have the intermittent low voltage or drop.  Driving a few miles would fix it ….or break it.  So, I installed a Hydraulic Battery selector switch.  I can run the slides off the House or Chassis or BOTH.  I had a 200 amp fused cable in the FRB from the Chassis as well as the House,  I have used the Chassis and no issues.  WELL   NOW I KNOW WHERE elusive 0.3-0.5 VDC drop is.  The issues in finding it was catching it when it occurred.  

After I jumpered the batteries, I checked the voltage (Magnum is charging or maintaining).  Less than 0.01 VDC difference,  AS EXPECTED.  So, I got curious.  At the Big Boy, on the Chassis stud…13.45 VDC.  On the House stud….13.12.  OPPS..0.33 VDC drop or difference.  NOW the fun begins.  I had removed my Salesman Switch solenoid a few years back when I was trouble shooting….to get to the House Cur Off switch terminals.  It is the preferred 300A Blue Seas.  It tested NO VOLTAGE drop then,  Today, when I did my checks, Inverter fuse (runs directly from the Battery bank) reads 13.45 VDC.  Then there is a cable to the Blue Seas….and the return or the “ON” cable goes to the House Buss with all the ANL fuses,  BINGO…13.13 there.  So, 13.45 INTO the Switch and 13.12 OUT.  That is the issue.  I have a spare switch and will replace it this next spring.  

So there it is.  Lessons learned and things NOT to do.  But, I have to close with a huge thanks to Frank McElroy.  As a once was an EE student and also in charge of maintenance for several large plants and did power distribution work as well as a hot rod gear head,  I understand how to trouble shoot.  BUT, our complex behemoths have an unusual, at least to me, structure and circuitry….and don’t get me started on the Dynasty.  The skill level needed surpasses normal automotive and “factory” maintenance skills.  I have learned so much working on mine and reading here and understanding and helping others troubleshoot….as well as having Frank  to ask and also explain…..it is an unbelievable transformation…..and I always am learning and curious.  He is a great asset.

That’s it.  


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  • Tom Cherry changed the title to Multiplex DISASTER Avoided & Big Boy Storage Bypass…WITH a BOGO ….Cause of Long Term Intermittent Electrical Issue
10 hours ago, isptbart said:

Tom - how do I determine which multiplex system I may have on my 07 HR Scepter & whether or not it would benefit me to have on of the CPU/controlers for my coach as a backup?


Bart from Virginia

You have what I call a hybrid or low end system. Only the Dynasty and above had a CPU.  Our system  uses the programmed switches to run the lights, water pump and vent fans. 

Each individual switch sends a command to a module ( three of them). They are alphabetical numbered like E, F G.  You can look at the legend where the 3 are located.  There are 10 circuits per module

For example the water pump may be Circuit 7 on Module F. You have Three Multiplex switch panels with a PUMP button or switch

Every time you push one of those PUMP switches, it send out a “F 7” CODE. 

That F 7 code then gets to Module F via a multiplexed signal over the Multiplex loop or circuit.  In our system, the IPX module or the EMS module is like the “Interpreter”.  Then that F 7 command goes to the F module. Every time you push the switch, it toggles ON or OFF

OK. Sidebar. The MPX switch in the center toilet on mine has 6 buttons. There is only a 3 wire MPX connector.

BUT that one switch module has 2 additional wires on a separate pigtail. Those two wires go to the water service Bay Area. When you push the remote pump switch there, it is like pushing the PUMP switch in the Toilet room. The remote switch’s contacts are in parallel with the toilet room pump switch

LIKEWISE, the overhead galley living fluorescents will come on from the switch on the passenger step well cover.  That switch is connected to the OVERHEAD light button on the MPX panel inside the MH.  So you have TWO switches for that Overhead light

ALL the other MPX panels do not have the extra 2 wire pigtail

SO, each MPX switch panel has a CODE programmed for each button. The center hallway bath fluorescent is on several MPX panels. So every time you push the CENTER BATH button on any panel, the CODE (say G 9) is sent from a switch and goes to circuit 9 on MPX module G

There are two different MPX modules.  Two are for DIMMING. The other is  a RELAY OUTPUT. TYPICALLY the relay output circuits are for on/off. Like the pump or vent fans or the fluorescents

The other two MPX modules have dimmer circuits. So if you hold in the HUTCH LIGHT button, the INTEPRETER keeps pulsing or dimming the Hutch Light.  The continuous signal tells the MPX module to keep pulsing and then sets a “intensity” chip for that circuit. The next time it comes on, it comes on at the same intensity 


NOW, if you had the large computer or CPU, it has a program and it has programmable logic and it is the INTERPRETER. you can program it to not extend a slide if the motor home is moving or not drop down a LED TV unless the slides are out

WE DO NOT HAVE A CPU. The IPX module or the EMS “clock chip” are NOT PROGRAMMED.  if it DIES, you buy a plug and play replacement. Each MPX module has DIP switches. So you buy the same Intellitec PN for say Module F. Then you set the DIP same as the original. Bingo. It works

THE MPX key pads are the only “programmed” items. I had mine backed up. But by knowing WHICH button goes to which module and circuit, you can have a keypad programmed. 

The two pads with the extra wires have to have the extra wires soldered on

Thats it. I’ll send you the pop quiz. Your posting privileges may depend on your grade.  LOL. 

Your question was great. But it took a long answer




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55 minutes ago, Tom Cherry said:

THE MPX key pads are the only “programmed” items. I had mine backed up. But by knowing WHICH button goes to which module and circuit, you can have a keypad programmed.

As if life isn't complicated enough, all you need now is an iPhone or Android app and a bluetooth receiver (Raspberry Pi?) in parallel with the MPX bus.  Is it on a standardized bus?  I'm volunteering @pwhittle to sort out the "details".  😉

- bob

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Tom - hey thanks for the info! Are the modules still available in case I need a replacement? Any other such related parts I should keep in hand?I have previously taken an inventory & made note of which switch activated which module & associated channel. Now.....if I can only remember where I put that inventory! LOL!

Many thanks!

Bart from Virginia

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12 hours ago, cbr046 said:

As if life isn't complicated enough, all you need now is an iPhone or Android app and a bluetooth receiver (Raspberry Pi?) in parallel with the MPX bus.  Is it on a standardized bus?  I'm volunteering @pwhittle to sort out the "details".  😉

- bob

Hi Bob,

That is my “Want to do” list, but I don’t seem to be able to get through mr “Have to do” list. 😀


4 hours ago, isptbart said:

Tom - hey thanks for the info! Are the modules still available in case I need a replacement? Any other such related parts I should keep in hand?I have previously taken an inventory & made note of which switch activated which module & associated channel. Now.....if I can only remember where I put that inventory! LOL!

Many thanks!

Bart from Virginia

Hi Bart,

The only thing that is tough to find are the Monaco specific keypads. 

I have been able to get a few at different times, but I only have a couple left.

Intellitec still makes keypads that will work, but they are a different size and would look different.


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Paul and Frank and maybe a few others here are the experts.  I know that the “Monaco style” keypads are getting scarce. Frank swapped me one out and reprogrammed it.  The labels slide in vertically so that is all you do. I THINK…..Memory, that I have three “6” and five “4” button pads.  Frank says EBay is drying up.  I know that my local, go to, electronically VERY ASTUTE, RV guy sends out “bad” keypads to M&M to be fixed.  They charge upwards of $400 if memory is correct.  

He does not have the skill set that Frank and Paul does nor the software.  There are, I think, two levels of “skills”.  The first is to read and program or reprogram a key pad.  We had a deceased member that could do that.  They can also copy and backup.  That is ALL that is needed for our hybrid systems as Paul indicated.  Knowing  how to add the auxiliary lead on the Bathroom toilet and the front light (with the door switch) is probably simple for Paul and Frank.

Bottom line, if you travel to or near Ohio City, OH (M&M) or go to our gathering….assuming Paul is there, get each individual switch backed up, but they can be “recreated” as well.  Took M&M maybe 20 minutes on my Camelot.

buy if you can find, one each.  But….be aware…gremlins lurk in the used switches.  Frank swapped mine, or he programmed and I swapped it.  There was a “tactile” bug in one button that turned on a light in the bathroom randomly…..M&M never was much help and I just kept experimenting and the circuits were reprogrammed and reversed and it stayed with the one button….  So a “new to me” keypad was put in service in 2018 and no ghosts since then.

Just learn from my UH OH and let the battery switch do the powering up and don’t have that momentary interruption.  I have a NetGear router that if there is a millisecond interruption or blink (lights) in my home during a windy day where a limb blows off and microscopictally blips the power, it gets funky.  Reboot and all is well…

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As for the slide motor protection, I have an 80a breaker on the firewall. My coach build was started in May 2007, so they must still have had an ample supply of 80a C/B’s then.


Once I converted ALL my lights to LED bulbs in 2009, I reset the #5 & #6 DIP switches on the two Intellitec light modules so ALL my lights dim in the Coach.  When fluorescent lamps were on a circuit, that was not an option. 

Since my coach was an early build for MY2008, I don’t have an IPX controller from all the searching on my part. When they were used, they were mounted on the wall, and visible, once the Intellitec module mounting panel has been removed.  Maybe a picture of an IPX module would help, if someone has one.

Where did you find yours, Tom?








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