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RE: Intermittent wiring problem (how do you debug it?)

To: "'Tim Economu'" <>,
Subject: RE: Intermittent wiring problem (how do you debug it?)
From: "Garner, Joseph P." <JPGarner@UCDavis.Edu>
Date: Wed, 25 Apr 2001 12:14:43 -0700
Also narrow down the search by following through the wiring diagram. Lost
the original post, but if you keep blowing a fuse, then you want to look for
shorts upstream (on the positive side) of the load bearing components. That
narrows the search even more. Look for burnt / frayed  / free-floating
wires, look for kinked/trapped wires, look for loose switches etc. look for
DPO modifications/splices. look for uninsulated connectors.  If you're not
blowing a fuse, then the most likely culprit is a dirty or loose connector
in the ahrness. Work through the diagram checking each connector in the
circuit. once you find the one that makes things work when you wiggle it,
then pull it apart, clean both terminals with a cotton bud dipped in
surgical spirit or nail-polish remover. Wipe dry. Reconnect, and gently
crimp if the connection is loose. Start under the hood. These connections
get dirties and looser more quickly than ones under the dash.

hope that helps



Dr. Joseph Garner
University of California
Department of Animal Science
One Shields Avenue
CA 95616

Phone: (530) 752 1253

> -----Original Message-----
> From: Tim Economu []
> Sent: Tuesday, April 24, 2001 8:27 PM
> To:
> Cc: MG List
> Subject: Intermittent wiring problem (how do you debug it?)
> Hi Jon:
> Intermittent electrical problems usually only "seem" 
> intermittent. In fact
> they are usually coincidental with something physical. Like 
> centrifugal
> force moving a wiring harness in a sharp corner, a solder 
> joint becoming
> more resistive (and less conductive) at cold temps, or a 
> switch contact
> shorting out to case ground at a certain place in its rotation.
> Try to tune in to what exactly is happening when the fuse 
> blows. Are you
> just starting the car? Is it hot? Is it on an incline? Do you hit the
> brakes? Once you find a link to something physical, usually 
> this will lead
> to clues about where the problem is.
> Alternately, if the thing really appears intermittent, you 
> can shake the
> wiring harness in all the places you can grab. What you are 
> trying to find
> is where a wire is bare and touching the frame (like going through the
> firewall or a grommet that is broken) or where two wires 
> might be touching.
> Other good places might be in the boot where your tool box or 
> tire might be
> grounding wires into the boot well.
> Kind regards,
> Tim Economu
> Electrical Design Engineer
> '69 MGBGT Which does have a name, and which also had an 
> intermittent brake
> switch that had to be replaced.
> +++++++++ contact info ++++++++
> Tim Economu
> Offgrid Engineering LLC
> 4131 Springwater Rd.
> Clinton, WA 98236 USA
> phone:  360-579-2117

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