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Old 11-20-2019, 09:10 AM   #1
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Join Date: Aug 2019
Location: Ohio
Posts: 361
Year: 2002
Coachwork: Thomas
Chassis: Freightliner FS-65
Engine: 7.2L Cat 3126 turbo diesel
Rated Cap: 71 passenger 30,000 gvwr
3126 electrical Q...

Victim is a 3126 engine in a freightliner with hydraulic abs brakes.
I've lost electrical function and can't figure it out yet -- see general thread here:
http://www.skoolie.net/forums/f33/el...ins-29423.html

MY QUESTION HERE SPECIFICALLY IS:
What is the minimum wiring needed to start and drive this engine?
I will need to drive the bus to it's winter location very soon about 10 rural miles from where it is now -- I don't need lights, heaters, bells, or whistles.
I probably don't even need the electrical power brake pump that backs up the hydro-boost from the steering pump.

Can I 'jump' the starter solenoid on the starter motor the same way I would with a car?

I know the ECM on the engine will need a steady 12v source to run -- I assume this power normally comes from the (ignition key switch) switched side of the fuse panel.

I was thinking of making a new positive cable and run it directly (with 40amp fuse and switch) from the starter motor positive post to the fuse panel.

Mostly I wanna make sure this kind of thinking won't cause me to fry my ECM or other expensive bits...
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Old 11-20-2019, 03:18 PM   #2
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Chassis: International 3800
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did you work on it at all today? work was killer again today for me to call you..


the big test id like to see is load test on the batteries,.. meaning a meter connected to POS and NEG on the batteries themselves and then a key on engine start attempt.. does that meter stay up high (above 11 volts).. or does it drop to nothing under load.. .. its important to measure at the batteries and not inside the cab just to prove the batteries are good
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Old 11-20-2019, 03:42 PM   #3
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Quote:
Originally Posted by cadillackid View Post
did you work on it at all today? work was killer again today for me to call you..


the big test id like to see is load test on the batteries,.. meaning a meter connected to POS and NEG on the batteries themselves and then a key on engine start attempt.. does that meter stay up high (above 11 volts).. or does it drop to nothing under load.. .. its important to measure at the batteries and not inside the cab just to prove the batteries are good
Just came home from the bus -- brought the batteries with me to recharge them overnight even though they still read 12.85v (I brought my better meter with me today which does read a tenth of a volt higher than my HF freebie meter I leave in my tool bag...)

The good news is that some of the electrical is restored. The gauge cluster came to life more normally with repeated turns of the ignition key. The electric door functions again. The back emergency door buzzed when I opened it, and the abs boost pump came on when I pushed the brake pedal.

With jumper cables hooked from the negative cable directly to the starter motor I got a more satisfying click of the starter solenoid. I did not have the huge voltage loss at the fuse panel when the ignition switch was placed to the run position but I still couldn't get the motor to turn over.
But even w/out the jumper cable hooked up measuring voltage between the negative post of the starter motor and the frame/ground I only had 12mv...

It would be odd that both my new batteries were somehow damaged but they're under warranty okay if they are... I agree -- a load test would be good -- hard to do with only two hands!

I'd be nice to throw a jumper pack on with my two charged batteries and see if that's enough juice to move the engine...
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Old 11-20-2019, 03:47 PM   #4
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makes me wonder if the ignition switch itself could be the culprit..
and you are right hard to think 2 new bats would die.. esp since they hold a top charge of 12.8 volts which ususlly indicates a nice healthy battery
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Old 11-20-2019, 03:52 PM   #5
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Engine: 7.2L Cat 3126 turbo diesel
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Quote:
Originally Posted by cadillackid View Post
makes me wonder if the ignition switch itself could be the culprit..
and you are right hard to think 2 new bats would die.. esp since they hold a top charge of 12.8 volts which ususlly indicates a nice healthy battery
I did try my remote starter switch as well on the starter motor -- that didn't seem to make any difference either...

I was thinking that bypasses the ignition switch but I guess that would only be bypassing the 'start' position of the ignition switch...

Yup, I'm open to suggestions...
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Old 11-20-2019, 04:23 PM   #6
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check the two big "white rodgers" solenoids. those are notorious for making electrical things not work.
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Old 11-22-2019, 09:33 AM   #7
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check the two big "white rodgers" solenoids. those are notorious for making electrical things not work.
Where do they usually live? I see you have a similar bus in your avatar.
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Old 11-22-2019, 12:32 PM   #8
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I'll go look this weekend. My bus doesn't have an access panel outside below the drivers window like every other bus I've owned. I've honestly never looked for em on this beast.
Does yours have an electrical compartment there?
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Old 11-22-2019, 12:38 PM   #9
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Quote:
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I'll go look this weekend. My bus doesn't have an access panel outside below the drivers window like every other bus I've owned. I've honestly never looked for em on this beast.
Does yours have an electrical compartment there?
Nope. Just the battery box further aft...

I've got most of the electrical panels loose now -- but it totally makes sense there's some big solenoids somewhere besides the starter motor...

I'll just trace the big wires coming up from the starter motor -- that seems to be the "battery bus" for this electrical setup...
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Old 11-22-2019, 12:59 PM   #10
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the solenoids are supposed to be accessory solenoids and on most thomas busses are located behind the switch panel for all the heaters.. one is supposed to be for Accessory position on the key and the opther is supposed to be for ignition position on the key.
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Old 11-22-2019, 05:30 PM   #11
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Join Date: Aug 2019
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Year: 2002
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Chassis: Freightliner FS-65
Engine: 7.2L Cat 3126 turbo diesel
Rated Cap: 71 passenger 30,000 gvwr
Quote:
Originally Posted by cadillackid View Post
the solenoids are supposed to be accessory solenoids and on most thomas busses are located behind the switch panel for all the heaters.. one is supposed to be for Accessory position on the key and the opther is supposed to be for ignition position on the key.
Yup. Interesting -- I only found one there. It was fine. It only has 3 posts though instead of the usual 4... Guessing it grounds through the body...
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Old 11-22-2019, 05:41 PM   #12
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Engine: 7.2L Cat 3126 turbo diesel
Rated Cap: 71 passenger 30,000 gvwr
Success!
It's running fine again!

Anti-climatic in that I'm not sure what fixed it...

1) recharging the batteries for 36 hrs...?
batteries currently (bad pun!) read 12.9v
I find it shocking (yeah, yeah...) that 12.75v wasn't enough oomph...

2) almost every connection has a little bit of corrosion -- none by itself was a problem according to the dvm but...

3) I removed, cleaned, and reinstalled every piece of wiring from the batteries to the ignition switch, and the + & - bulkhead connections.

Hopefully letting it run for 30 min was a nice sonic vibe for all the wiring...

After all that -- I only read .1mv from the negative battery post to the chassis. That would imply my parasitic drain issue is gone too but I disconnected the batteries anyway...
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Old 11-22-2019, 05:45 PM   #13
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Rated Cap: 7 Row Handicap
my red bus only has one, everything that works on IGN works on accessory except the computers dont power up for the engine on Accessory.. that solenoid is for body accessories.. I was trying to find some 3126 diagrams for the FS65, most of what I find are for the MVP and HDX models which are different animals..



I had thought someone here posted a google drive link to a bunch of freightliner wiring diagrams
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Old 11-22-2019, 05:46 PM   #14
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fantastic you nailed it!!!! ignore my last post
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Old 11-22-2019, 05:50 PM   #15
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Quote:
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fantastic you nailed it!!!! ignore my last post
Not at all -- if your red bus only has one, than most likely I'm not "missing" anything... I have no baseline of what happened from 2014 when the school district sold it to 2017 when BrewDog acquired it -- I only know BrewDog parked it so 3 years of dust and decline...
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