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Finding parasitic loads?


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Fixesbigyellowthings
Novice

Sep 11, 2016, 4:57 PM

Post #1 of 7 (1025 views)
Finding parasitic loads? Sign In

Ok so I have a van ( 02 Ford E450 cut away school bus) that's dead nearly every morning. Getting about a 7 amp parisitic load with ignition off. Yanked every fuse and found no concernable reductions in amperage. Checked the charge/start system for worn insulation shorts etc. No luck there. Both batteries test good.

I've done this a 100+ times ,What am I'm missing this time round ? I've spent hours looking for this one.

Most of the original accessory wireing / school bus componts have been removed, use it as a cheap camper.......bad cross gate and stop sign stop position switches have led to more jump started schy busses than I can count.


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Sep 11, 2016, 5:21 PM

Post #2 of 7 (1015 views)
Re: Finding parasitic loads? Sign In

You're not testing it correctly.

There is a procedure for finding a battery draw like that.

You will need a digital ammeter and a jumper wire with clips on the ends to do this.
First rig any door switches so you can have a door open without triggering the interior lights and unplug the hood light. Remove one battery cable and attach the meter in series between the battery cable and battery post. Take the jumper wire and also attach it the same way. Leave the jumper wire on for at least 10 minutes to expire all the automatic timers. Now remove the jumper wire and read the meter. Anything over 50ma is too much draw. The way you locate this is to start removing fuses one at a time until the meter drops to normal level. This will be the circuit with something staying on. Determine what components are part of that circuit and check them individually until the problem is isolated.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Fixesbigyellowthings
Novice

Sep 11, 2016, 5:32 PM

Post #3 of 7 (1012 views)
Re: Finding parasitic loads? Sign In

Sorry should of said more. Yes the ampmeter was placed between batterys and pos cables, before I started pulling fuses. Bit of a nuisance to do on these buses...one battery is under the hood and one is mounted to frame half way to the back.


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Sep 11, 2016, 5:34 PM

Post #4 of 7 (1010 views)
Re: Finding parasitic loads? Sign In

It doesn't sound like you let the timers expire.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Fixesbigyellowthings
Novice

Sep 11, 2016, 5:54 PM

Post #5 of 7 (1006 views)
Re: Finding parasitic loads? Sign In

I normally attach the jumpers before disconnecting the battery to avoid having to wait. I'll try the other way to and wait to see if it changes my reading.

Ive blown a dmm connecting larger busses. Can see 40+ amp spike right when you hook the batteries up. The Multiplex controllers likes to cycle every thing on.


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Sep 11, 2016, 6:01 PM

Post #6 of 7 (1002 views)
Re: Finding parasitic loads? Sign In

Are you locking out the door switches and hood lights before you get started.

Many times pulling certain fuses will wait up the modules over again also.

seven amps is a lot. that will kill it in a matter of hours. That should be something very noticeable.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Fixesbigyellowthings
Novice

Sep 11, 2016, 6:23 PM

Post #7 of 7 (999 views)
Re: Finding parasitic loads? Sign In

Going to check a couple things, three switches are built into the side entrance door. A rotating cam depresses them at.different times depending the Door position. One won't allow the vehicle to shift in to gear if the door is open, other two are light switches. Interior lights, and 8 way activation. I've disconnected the lights but the 8-way controller is still there. Could be waking something else up.






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