Electrical Gremlins: Batteries draining when off

[daveola]

I thought dealing with the electronics on my British car was difficult, looking at the mountains of spaghetti wiring in my bus is a bit overwhelming.

First off, MCI 102A3.

Currently I'm having a problem with my bus batteries discharging when the bus is sitting.  If I was leaving the bus in storage, I'd just cut the master switch in the battery bank, but I currently drive/move the bus every few days, so that's a hassle.

Regardless, with the power off (at the dashboard) on the bus, I figure that the batteries shouldn't be draining (the batteries are reasonably new, so it's not just a dead battery issue).

One thing I noticed that surprised me was that the CB inside the electrical panel has power even when the bus is turned off.  Seems that shouldn't be the case.

I also seem to recall that my parking lights would go off when I turned off the bus (with the dashboard power switch) - but now they're left on and I have to shut the lights off at the dash as well.  Used to be that I'd turn off the power at the dash and all my lights would go off, no power drain.

Makes me wonder if there isn't some accessory relay that's getting stuck on somewhere and is feeding the lights/CB/etc, and that's where my power is going.

So, to start, three questions:

1) What turns power off to the CB?  Isn't this supposed to be controlled by the dashboard power?
2) Are the parking lights on a 102A3 supposed to be controlled by the dash power?
3) Any suggestions on how to figure out where the power is going?  So much of the wiring is internal to the bus, it seems a bit like decoding a black box.

Thanks!

[Busted Knuckle]

Dave your asking a loaded question!

MCI's have always had a problem with battery drains which is why they come with a main cut off switch in the first place!

FWIW operators that run them tell the drivers to shut the power off anytime it's going to be parked 10-12 hrs or overnight.

Also SO many of these buses have had many different owners and mechanics working/playing with the wiring it's hard to say who's done what to them.

And on top of that CB's were not generally an accessory installed by the factory so again it's only ANYBODY's guess as to who wired it, and where!
  BK 

[Lin]

As mentioned, there is no way to know what any previous owner has done, so you may have to track down where the circuits in question are getting power.  It can be very daunting looking at the mess of wires, but you can work your way through it.  You can buy a tone generator that will make tacking circuits relatively simple.  Start with the CB, for example.  It seems to be connected to a hot, or at least the hot side of the main switch.  You can leave it or move it.  The same goes for the parking lights.  However, you could be right about it being through a failed relay.  There is no way of knowing until you track it down.

You can use an ammeter at the battery to see what the draw is when the dash switch is off and try to track down where it is going.  If there is no draw at the battery when the dash switch is off, it would point to a bad battery.  You can of course, charge and test the batteries.  Also look for any old switches that you may believe to be inactive but may not be.  Turning the main disconnect off in the meantime will be a good practice.

[daveola]

Sure, but what's weird is that it didn't use to have a battery drain.  I could leave the bus for weeks and the batteries could start up the bus no problem.

The discharging developed and ruined my old batteries, so I put in new batteries, but it's still discharging.

More importantly, I didn't use to have to switch the lights off.

So that brings me back to one of my original questions.

If the lights are on, but you turn off the power at the dash, do the lights turn off?

[Nick Badame Refrig/ACC]

Also,

Very common with 102's are baggage compartment lights that don't shut off when the door closes.

Get inside and check them out! 

Good Luck
Nick-

[dougyes]

To solve this same problem (on a 102-D) we put a heavy duty cut off switch on the lines going from the batteries to the Vanner Equilizers, and turn those off when we shut off the main. If you look at the wiring in the battery compartment, you'll see the fat wires going from the battery to the main cut-off, but there are smaller ones going directly from the battery to the Vanners and maybe elsewhere. Put switches on those to completely isolate the batteries and you've solved the problem.

[daveola]

As mentioned, if I hit the main cutoff switch in the battery compartment, I don't have a problem.

My problem is that is phantom power now if I turn off the master bus power on the dashboard.  I hear that other people are experiencing this as "normal" but this used to not be the case with my bus, and now it suddenly is.


And again, I'm still hoping someone with a 102A can run this quick experiment:

Turn on the "Clear ID Lamps" switch on the dash, with the dashboard master power off and the battery cutoff on, and tell me if you have any parking/tail lights on?

[Len Silva]

It's very likely that you have a bad ground somewhere.

[daveola]

A bad ground as in a ground that isn't fully properly connected?  How would that cause a drain while bus master power is off?

Or do you mean a neg terminal somewhere that's supposed to be switched but is instead shorted to ground?

[bevans6]

If you grab a schematic and trace the exterior lighting circuits just as an example, you'll find that an awful lot of it does not go through the dash master switch.  A quick glance shows that turn signals and running lights have direct connections to the master bus.  In other cases, the master switch simply controls circuit elements that switch relays on and off, and the load portion of the relay goes directly to the master bus.  In other words - the master switch on the dash in no way disconnects significant portions of the bus electrics from anything.  It's a bit of a misnomer to call it a master switch, to be honest.  It is in no way a master bus power switch, as you characterized it, not in any way, shape or form, and it's only connected to the front panel bus anyway. There are at least three other main 24V bus bars in the system.

I also found that if you have a Vanner, it can discharge batteries pretty good all on it's own, if one of the batteries is weak.  That battery goes down, the Vanner forces the voltage up by drawing from the other battery, and it cycles to zero.  In my case, the keep-alive on my car radio connected to 12 volts was wired wrong, and that parasitic load drew my batteries down to zero over about a month.  They did recover, which shocked the heck out of me, but they were at 1.2v and 0.8v when I found them.  You will also find that the 12V feed in the main bus panel is directly connected to the center tap on the batteries, no master switch.  Everything in the AC panel and the rear engine bay panel is directly connected.  All it takes is a little corrosion in one relay to start to draw down the batteries.

Hence - the real master power switch - the battery cut-off...

Brian

[Mike in GA]

Dave - I have a 1985 MC 96a3, probably very similar to your 102.
     To directly answer one of your questions, with the ignition (main) dashboard switch in the off position, the headlights turn off automatically. In fact I leave the headlight switch "on" always so that I routinely drive with 'lights on for safety'. They go off when I kill the engine. However with the dash switch off, I can still turn my clearance lights on and off - and this too has always been the case. I suspect MCI manufactured them this way.
     Another stab at part of your problem - the CB...  some CBs with a weather channel are wired in a way that even when they are turned off, an emergency extreme weather report can automatically turn it on temporarily. Sounds strange, I know.
     And FWIW I always kill the main battery switch down in the battery compartment when stopping for the night. A bay door left open or ajar will keep that bay light burning all night, and that will run down weak batteries.
     Hope that helps.
Mike in GA

[thomasinnv]

I actually had forgotten about the bay lights. I disconnected mine when I got the bus. I had intended on switching them over to the house bank and installing a main cutoff switch in the dash for the bay lights, but like so many other projects, never got around to finishing it.

[bevans6]

On the MCI MC-9 schematic I have, which is probably identical in this respect to the 102 or the 96, the clearance light switch is directly connected via a 3 amp resetting breaker to the main bus bar in the forward electrical bay.  Turning it on energizes the control coil for the running light relay. so the running lights turn on, and also energizes one terminal on the master switch.  The other side of that terminal on the master switch goes to the headlamp switch.  So - to turn on the headlamps, you need both the clearance light switch on and the master switch on, but the clearance lights are not controlled by the master switch at all.

Brian

[daveola]

Thanks for all the information.  I hate the idea of having to go into the battery bank everytime I want to move the vehicle, but maybe that's what I'll have to do.

It certainly doesn't fit into my zombie defense plan, being in the bus and having to somehow go outside to move the bus. 

I thought about putting a power relay in there that I could control from the dash - I have large relays that can handle that current, but the idea of a relay/wiring failure suddenly killing all my power while driving turned me off to that idea - I once had something hit the dashboard master switch while driving in the mountains and my engine and lights went off.  If I hadn't realized what had happened and flipped the master switch back on, then I wouldn't be typing here today.

[buswarrior]

Move the battery cut off into the coach, or cut a hole to reach it, if that will ease your mind.

Also, does the coach still have the PA system?

Pull all the plugs on that little devil too.

Stuff that works as we inherit the old coach from its last commercial operator starts to not work due to lack of use. Stuff sticks, stuff corrodes, it only kept working because it was kept working.

There are various headlight wiring strategies, both factory and fleet installed, as busnuts move into the 102 years. Daytime running light systems, working or not, all with relays and/or solid state switching gear can be a pain after years of second rate maintenance attempts.

happy coaching!
buswarrior