Electrical... From Bad to Worse

Glennman · October 17, 2020, 10:04:56 PM

Well, I believe you are all aware of my issues with the wheelchair light on the dash, and no throttle, shifting, etc.

Well, today I went out to look at trying some ideas on taking care of the problem of the wheelchair light causing the throttle and shifting inhibitor to kick in. At least the engine would start and run, but of course no throttle, shifting, or high idle. Now, there is nothing. No starting, no dash lights, nothing. I have full 24 volts at the batteries, the main cut off switch works, otherwise dead. It would start and week ago, now...(?)

After leaving the "on" switch on for a few minutes, the headlights came on, some of the dash gauges including the speedometer started jumping up and down, at the pattern of a turn signal. I would shut it all off and back on again, back to totally dead. I haven't done anything to it since the last time I ran the engine.

This is getting very discouraging. I think I need to hire an MCI person to make a house call and look at all this and give me a rundown on how all this works. I have been making some contact with an MCI field representative, but only a few emails. I'll have to have them come out, even if it costs a few bucks.

fortyniner · October 18, 2020, 05:34:40 AM

Grounds.

Unrelated equipment affecting each other in my experience is often due to poor/corroded grounds. It can cause bizarre behaviour.
Any ground exposed to periodic moisture is suspect even though it may appear ok. Take it apart inspect and clean. I usually follow
with something ike CorrosionX or Boeshield to try and protect it after cleaning.

-Tom P.

hogi6123 · October 18, 2020, 06:17:25 AM

With a wiring diagram and voltmeter, you can trace where there should be voltage and find where it is interrupted. It will take a while but will be worth it in the end.

blue_goose · October 18, 2020, 06:35:59 AM

The problem is you have opened the ground for the lift sensor. One of the wires that you disconnected when you took out the lift was the sensor wire that needs to be going to ground. The wire will not be showing any voltage, so you can check and ground any wire that you opened that doesn't have voltage and see if that stops the problem.
You can turn the switch off with a prolink or computer with the Detroit program.
Hope that helps
Jack

buswarrior · October 18, 2020, 06:47:00 AM

If all you did was shut off the big battery switch...

What exactly is the battery voltage? On both batteries by themselves? "24 volts" isn't enough, they're dead.

Unless you isolated ALL the wiring in the battery compartment to beyond the battery switch, there are parasites that drain it down through the week...

The quick and sure way is pull the cables off the battery posts when the bus is stored, until these things get isolated.

Happy coaching!
Buswarrior

richard5933 · October 18, 2020, 06:58:03 AM

Amazing how a poor ground connection can hold on for dear life, and then once the batteries are disconnected it decides to let loose.

luvrbus · October 18, 2020, 08:47:47 AM

Quote from: Glennman on October 17, 2020, 10:04:56 PM
Well, I believe you are all aware of my issues with the wheelchair light on the dash, and no throttle, shifting, etc.

Well, today I went out to look at trying some ideas on taking care of the problem of the wheelchair light causing the throttle and shifting inhibitor to kick in. At least the engine would start and run, but of course no throttle, shifting, or high idle. Now, there is nothing. No starting, no dash lights, nothing. I have full 24 volts at the batteries, the main cut off switch works, otherwise dead. It would start and week ago, now...(?)

After leaving the "on" switch on for a few minutes, the headlights came on, some of the dash gauges including the speedometer started jumping up and down, at the pattern of a turn signal. I would shut it all off and back on again, back to totally dead. I haven't done anything to it since the last time I ran the engine.

This is getting very discouraging. I think I need to hire an MCI person to make a house call and look at all this and give me a rundown on how all this works. I have been making some contact with an MCI field representative, but only a few emails. I'll have to have them come out, even if it costs a few bucks.

Once you get the concept of breaking the system down into 2 parts the OEM reasonability and the DDEC reasonability they are not that hard to trouble shoot hang in there

Glennman · October 18, 2020, 08:56:42 AM

Okay, so from what I'm getting here is grounds and low batteries.

The grounds are easy enough, and granted, there are some questionable looking ground connections.

But the 24 volts? 24 volts is considered dead? I have a 24 volt trickle charger, but how much is enough? 28?

Melbo · October 18, 2020, 09:03:24 AM

My bus likes to be in the mid to high 25's when resting. Immediately after shut down it will be 26 and change and then settle at 25.8 plus or minus a tad. That is with the batteries completely isolated.

HTH

YMMV

Melbo

buswarrior · October 18, 2020, 09:12:15 AM

As melbo noted.

Battery voltage is a many paragraph explanation and cautions to measure it with some meaning.... but a 12 volt battery that has sat for a week should show at least 12.6 volts for full charge. Also, measuring the voltage after a short load is put on it, headlights, starter, also is a good indicator.

So one start attempt and batteries are found below 12.6 each, they are not up to par. And i emphasize EACH, because lots of engines are looking for the 12 volt, not the 24 volt for the computer, and it will be the computer related battery that is likely harmed.

No happy computer, no engine function

Happy coaching!
Buswarrior

luvrbus · October 18, 2020, 09:15:09 AM

Quote from: Glennman on October 18, 2020, 08:56:42 AM
Okay, so from what I'm getting here is grounds and low batteries.

The grounds are easy enough, and granted, there are some questionable looking ground connections.

But the 24 volts? 24 volts is considered dead? I have a 24 volt trickle charger, but how much is enough? 28?

If and when I get back to the shop I can send you a laminated copy of the OEM side of your bus if I have one left,the problem 98% of the time is on the OEM side so don't rush out and buy the 500 page trouble shooting manual for the DDEC it will be no help to you

luvrbus · October 18, 2020, 09:28:18 AM

Quote from: Glennman on October 18, 2020, 08:56:42 AM
Okay, so from what I'm getting here is grounds and low batteries.

The grounds are easy enough, and granted, there are some questionable looking ground connections.

But the 24 volts? 24 volts is considered dead? I have a 24 volt trickle charger, but how much is enough? 28?

Me I check the voltage at the starter and work back to the batteries it saves time

Glennman · October 18, 2020, 09:44:27 AM

I really need a quality charger, but I put my 24 volt trickle charger on it, and it instantly says they are at 100% and 24.7 volts. The batteries are only 2 months old. If the trickle charger says 100%, them I'm sure it will not put more in. I suppose I can pull out the batteries and check them individually, put my 12 volt charger on them one at a time and see what I can get them up to.

I'll be in the market for a charger that will do both, so if anyone has any ideas on the best to get, let me know.

richard5933 · October 18, 2020, 09:57:21 AM

Here's what I use to keep the 24v batteries charged on my bus:

https://www.progressivedyn.com/specialty/pd9225-battery-charger/

If you plan on being able to charge them once the conversion is done, you'll need something better than the trickle charger. Those things are horrible, IMO. This PD charger is a smart charger and will cycle the voltage to a proper maintenance level once they are fully charged, and it brings up the voltage once a day to avoid sulfation.

ktmossman · October 18, 2020, 11:37:03 AM

I was chasing an electrical gremlin last week with my trans. The Allison keypad would just flicker an asterisk on the readout. I had the MCI guy with the computer trying to chase it and it really stumped us. It would not let the computer over-ride any of the switches. He checked the voltage on all the switches and at the fuse box. (Note: My MCI guy used to work at the MCI shop in Dallas and now has his own business. He charges less than HALF of the MCI shop rate. The key is that he knows those busses like the back of his hands including the Multiplex. He is my new BFF.)

Turns out that there was a ground bolt through the panel between were the HVAC heater core used to be and the electrical area. I had taken it out when I pulled the electronics from the heater out to get the heater core out. What I didn't realize was that on the opposite side of that panel, the trans wiring had a tiny ground wire ground connected to the same bolt, which was now hanging free. Put a new bolt through with that ground wire on it and all was well...very annoying.