trace short causing battery drain help

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Jan 2, 2011 | 03:57 PM

msteelsos

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trace short causing battery drain help

77 f350 suddenly battery low or dead in morning.
Alternator charging, battery taking charge, runs fine all day.
Disconnect battery at night, still have charge in morning.
Pulled positive side and hooked up voltmeter bewtween pos terminal and cable.
Read voltage.
Pulled fuses, still have voltage.
Disconnected solenoid on battery side, voltage only when wire to cab is hooked in. (There are two accessory wires plus battery cable.)
Ant suggestions on further logical steps to isolate this short?
Everything on the truck functionsw fine - lights, radio, heater, horn, flashers etc.
Thanks

Jan 2, 2011 | 04:14 PM

fmc400

MSEE

Joined: Apr 2004

Posts: 10,386

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From: Austin, TX

Try removing the connector to the headlight switch. The headlight switch is not protected by the fuse panel, but is instead protected by an internal circuit breaker. If there is a leakage path there, it will still show up with all the fuses removed.

Also, one side note: it's much safer to work with the negative battery terminal instead of the positive terminal. The sheetmetal around the battery is grounded. If you ground out your wrench as you're removing the positive battery cable with the negative battery cable connected, it will not be a good situation. As such, always remove the negative battery cable first, and put it back last.

Jan 2, 2011 | 04:34 PM

bmuhlbach

Cargo Master

Joined: Dec 2006

Posts: 2,511

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From: hinckley ohio

voltage regulator my be bad its located on core support by the battery

Jan 2, 2011 | 04:50 PM

Action4478

Hotshot

Joined: Aug 2006

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voltage regulator is the first thing I would test ..

Jan 2, 2011 | 04:52 PM

msteelsos

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clarification

The solenoid has four terminals= bat in starter out, s and i.
on the bat in terminal are three wires= battery, cab supply and voltage regulator.
The only time I get voltage is with the cab supply connected.
No voltage except from the battery to the cab supply.
Checked the s and i, no voltage.
As an add test, I just pulled all fuses at the same time- no fuses in box and still have a voltage reading.
Since these trucks can have lights without key on, there has to be some short somewhere between the solenoid terminal and the fuse box,
Any suggestions for tracing this appreciated.
Since the truck is all original (side spare, extendable bumper, plastic rear tank etc)
I do not want to start randomly pullin things apart. Wiring is also original.
Still getting 14 mpg at 170,000 w 351m.
Any help?

Jan 2, 2011 | 04:56 PM

havi

I'll have the Roast Duck

Joined: Jul 2002

Posts: 9,622

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From: Northshore, MN

headlights and warning lights have their own circuit breakers independent of the fuse box, so I would disconnect them, too. (fmc400 touched on this)

Jan 2, 2011 | 05:08 PM

msteelsos

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headlight switch

fm400, did change to neg test.
headlight switch next. Missed the posts while I was testing and [posting.
So I will figure out what has power without key on and begin with headlight switch.
Any other suggestions?
Thanks