Rewire the Entire Bus

[Glennman]

After watching the video of the gentleman who completely rewired his bus (the Cobb gentleman, I believe), I got to thinking, my D4500 with all of its black boxes, ring system, multiplex (whatever you call all that stuff), why can't all that stuff be eliminated? Keep the ECM for the engine, but get rid of all the redundancies. There are buses out there that do not have all that, but they have a Series 60 engine, Allison transmission, lights, gauges, etc. My point being that all that stuff can work without all the redundant systems. Am I crazy here?

[Brassman]

I say the desired end result would be reliability.  In my thinking you can get there two ways; with redundancy, which makes things complex; or with simplicity, which makes things critical. 

There's got to be a sweet spot somewhere between the two.

[TomC]

One of the many reasons I chose a transit bus. Simple wiring like a big rig truck with straight 12v wiring. I eliminated the door interfaces and was left with a simple wiring system anyone can understand.

As compared to the cluster (you know what) that I've seen on Prevost buses converted by Marathon (unbelievable). Good Luck, TomC

[buswarrior]

Multi-plex replaced the miles and pounds of wiring that an older coach was built with.

A communication cable instead of the giant bundle of wires front to back.

Not impossible... the problem is that peeps can't BS their way thru the multiplex system... one needs to know what they are doing... 

Learning how to tame the beast, vs building a wiring harness for a bus without one...

I guess it comes down to how one wants to spend one's time and resources?

Happy coaching!
Buswarrior

[chessie4905]

My thought,unless you are really good with wiring, this is a quick way to become overwhelmed and end up parting out the coach or trying to find a buyer. "For sale- coach shell, great condition, needs complete wiring harness to start, run, and drive". Especially so when we've had posters remove some wiring by baggage racks and things important don't work anymore.
Think this over carefully. Easy to get in over one's head.

[luvrbus]

Why those systems don't give many problems most of the time the electronics for the engine and transmission give you the problem the system you want to keep.My RV is loaded with electronics for the house system the only problem I have had when I changed to all LED lights the goofy Tsat for the AC and heating systems went crazy and cost me $125.00 for a Tstat that was compatible with the LED's ,Those systems are proven you just cannot be cutting and splicing in wires or you have a mess on your hands
   

[luvrbus]

One of the many reasons I chose a transit bus. Simple wiring like a big rig truck with straight 12v wiring. I eliminated the door interfaces and was left with a simple wiring system anyone can understand.

As compared to the cluster (you know what) that I've seen on Prevost buses converted by Marathon (unbelievable). Good Luck, TomC

Those systems can be repaired 99% of the time over the wifi and cell phones by Marathon they log into the system 2000 miles away and you can watch it being checked amazing Cummins can do that on my engine lol all for a fee which is not that bad

[ktmossman]

The key to the multiplex simplification is finding someone who knows it well AND has the computer program for it.  I found a mechanic who used to work at MCI and has the computer program.  I paid him a couple hours of labor to clean up all the wiring in the back and will do the same for the front.  This eliminates all the "passenger amenity" wiring that is no longer needed, leaving only the parts of the overhead harness needed for the engine and the marker/brake lights.  I will still have to find a place to tuck the primary front and rear junction boxes (which used to be in the driver's side overhead bins) in cabinetry, but they don't need to be visible.

[Jim Blackwood]

One of the reasons I looked for a '95-'96 coach. This one has DDEC4 and a panel in the front bay for transmission control but conventional wiring otherwise, so I don't have to worry too much about goofy things happening because I happened to break a wire, which can happen by accident. Sometime after covid I plan to get down to MCI in Louisville and order  the manuals so I can get complete schematics but in the interrim that lack is not slowing me down.

I invested early and rather heavily in electronics, eventually to learn that I'm better off to keep things just as simple as I can and consider all of that stuff black magic and best avoided if possible. Not that I've done too well at practicing that but I do keep getting burned by it, especially any time I wander into new territory. Which has made me reluctant at best. I do think it's great that for some people it just drops in your lap and does what you want with little or no effort. But that's not me and I've wasted far too much time and effort on it already. I don't think I'm anybody's dummy but you do need to be smart enough to know when to quit. So for the last few years my approach has been to stick with the tried and proven, avoid anything that creates headaches of any sort, and keep the invisible complexity to a minimum. That seems to be working out OK.

Jim

[Glennman]

The key to the multiplex simplification is finding someone who knows it well AND has the computer program for it.  I found a mechanic who used to work at MCI and has the computer program.  I paid him a couple hours of labor to clean up all the wiring in the back and will do the same for the front.  This eliminates all the "passenger amenity" wiring that is no longer needed, leaving only the parts of the overhead harness needed for the engine and the marker/brake lights.  I will still have to find a place to tuck the primary front and rear junction boxes (which used to be in the driver's side overhead bins) in cabinetry, but they don't need to be visible.

ktmossman, send me a private message (if you wish) of the person's contact information, and I'll fly him here (if he wishes!) to work on my bus. I hired a local bus mechanic and haven't heard back from him in 2 weeks. He looked it over and left, saying he will do some research, and I haven't heard back. It would be nice to have someone as back up, in case this guy doesn't come through. Thanks.

[luvrbus]

Did you ever run the vin on your D with MCI to see if it had the multiplex system they were a option on the D and standard on the J's and E's,The software people are getting greedy now they want a annual subscription fee and it is exspensive for buses my JPRO has leaped to almost 5 grand a year. I am not going to pay it lol I paid Allison $140.00 to program my B500 because Allison was wanting $900.00 per year to renew my subscription   

[oltrunt]

I expect the Multiplex Monster is here to stay and from what I've just read here I'm feeling a little less sheepish for having spent $1,500 on a dealer level diagnostic system for my insanely multiplexed Isuzu chassis and drive.  Jack

[mqbus767]

Glenn,

I'd think hard and long about rewiring your bus. And then I'd think again and wait, then think again. Once you rewire it, you no longer have a D4500 on your hands so you'll be on your own for any electical help. Granted, much of the multiplex system is dedicated to passenger comfort/safety devices that are of little value to a bus conversion, but many other devices (head lights, blinkers, marker lights, etc.) rely on it. Your bus was designed from the factory to support that multiplexed system. A major benefit of multiplexed systems is the reduction in wire.

If your motivation to rewire it is out of fear (unknown tech., obselence, "complexity"), that may not be the best perspective to make such a decision. Once you start cutting and removing, things get deep quick. If the current multiplexed system gave you another 5-10 years of reliable operation, why not tackle any breaking/obsolescence issues then? Consider that our buses are 20 or so years old now and you can still get Dinex multiplexers on E-bay for 100-200 USD.

You might start by considering how you'd replace a single system that is currently being handled by the multiplexers with a traditional long-haul replacement. Take, for instance, the flashers. Currently your multiplexer senses the turn signal switch (left or right) is pressed, sends a signal to a multiplexer at the back of the bus that raises an output pin high/low, which switches a relay on/off, and flashes the signal light on/off. That same path gets used for the 4-way flashers with the only difference being the 4-way switch on the dashboard. Headlights, markers, etc. work the same.

Now consider replacing system with long-haul wiring. You've got several new runs of wire, front to back. You'll need to add flashers to the circuit because before the multiplexers were doing this. You'll need to need to tie into the relay circuit for the lights or replace it with your own. And, you'll have to figure out and rewire your dash switches to power the flashers. At the end of the day, I'd be surprised if you have a less complicated or even equally reliable system as the one that is currently in there.

I understand the fear of the black boxes and it's warranted to some degree. MCI, and I imagine other makers, change their multiplex networks every few generations. Those black box vendors are a mixed bag when it comes to sharing information about troubleshooting and access. Depending on what your bus was used for in it's past life, you might have a ton of non-factory add-ons that can immediately come out. Our bus was a Houston commuter bus and had mutliple generations of telemetry equipment layered on it. (Check my thread starting here: https://www.busconversionmagazine.com/forum/index.php?topic=33689.msg387408#msg387408) Removing that stuff and getting back to factory only wiring was a huge mental win for me.

The advantage of our multiplexed system is we enjoy lots of short run, tiny AWG wires to end devices. If you have access to the manuals, you also get a system that tells you what's wrong through LEDs and flash codes. Although it would be nice, you don't always have to have the uber expensive tools and software to troubleshoot everything. Digital, by it's nature, is on/off, 1/0, working/not working. Maybe one day down the road I'll even get into hacking on the network so I can build my own diagnostic tool. Then, the entire bus opens up to me (OBDII for the running gear, Dinex for everything else)

[chessie4905]

Your argument seems to help to consider rewire. On the old design, if turn signal doesn't  work, check for voltage at bulb, replace bulb or flasher if none flash. In the multiplex system, you are going to need manuals, diagnostic reader, open line to a tech. I know that the new systems are pretty reliable, but a total cluster to save wire. No wonder they drop in price so fast. Bus companies unload them when electrical troubles start. They don't  want to pay big $$$ for an hourly tech on site to deal with these issues. Same thing with newer cars and trucks. They are mostly reliable, unless you end up with a lemon or as age and corrosion starts. Imagine when they get as old as a 4104.

[dtcerrato]

Anything now a days would be dead a lot sooner than the life span of an old bus but you already said that...