One word of caution: never make ohm measurements on a live circuit.
Disconnect one of the battery cables before setting the meter to ohms.
Bob Donahue (Still stuck in the '50s)
Email - bobmgtd@insightbb.com
52 MGTD - NEMGTR #11470
71 MGB - NAMGBR #7-3336
.
----- Original Message -----
From: "MonteMorris" <mmorris@nemr.net>
To: "Barney Gaylord" <barneymg@ntsource.com>; "MG list" <mgs@autox.team.net>
Sent: Thursday, June 20, 2002 10:15 AM
Subject: Re: blowing fuses
> Thanks, Barney.
> And yes, you're right I wasn't checking continuity correctly. You pointed
> out my stupidity without being offensive; maybe you should have been in
> politics :) If I had only thought what the word "continuity" means I
could
> have figured this out. DUH.
> I was checking using the ohm meter and touching the black lead to ground
> and the red lead to the end (one end) of the wire at the fuse box end. So
I
> assume I wasn't checking for anything besides current but using the
ohmmeter
> scale?
> So maybe it was just a bad connection.
> One of the many great things about this list is that I can learn as I go
> and you all don't charge me $70/hour :-).
>
> Monte 79B, 67B, and 74 1/2 parts car
> Kahoka, MO USA
>
>
>
> ----- Original Message -----
> From: "Barney Gaylord" <barneymg@ntsource.com>
> To: "MonteMorris" <mmorris@nemr.net>; "MG list" <mgs@autox.team.net>
> Sent: Wednesday, June 19, 2002 11:56 PM
> Subject: Re: blowing fuses
>
>
> > At 08:23 PM 6/19/02 -0500, MonteMorris wrote:
> > >.... 67B, which had been blowing the bottom fuse as soon as I turned it
> > >on. .... take all three green wires off the fuse terminal and plug them
> in
> > >one at a time to see which one blows the fuse, and/or check
> > >continuity. Two of the wires caused the short and both had no
continuity
> > >when tested. Why would two wires be shorted in this circuit?
> >
> > Two green wires shorted together and grounded could be a result of a
short
> > or overload in one circuit that melts the insulation in the wiring
harness
> > to short the two wires together and to some point on the chassis at the
> > same time. But that sort of a short does not usually clear up just by
> > moving the wires about.
> >
> > Not having continuity doesn't sound right. If the two wires are both
> > grounded they will abviously have continuity between them. The only way
> > they don't have continuity from one end to the other is if they are
broken
> > or cut, in which case they probably wouldn't work again after just a
> little
> > fiddling. Or there may be a loose connector somewhere in the middle of
> the
> > wire run that you are overlooking, but this is not likely to affect both
> > wires exactly the same before and after the fiddling. Too many
> coiincidences.
> >
> > Are you sure you are checking continuity correcty? Maybe you should try
> > disconnecting both ends of the wire when checking for a short to ground,
> as
> > a connection to an electric motor can have a very low resistance when
the
> > motor is not running. Also check for continuity with the meter test
leads
> > on opposite ends of the same wire. When multiple green wires go through
a
> > harness it's hard to say which is which where they emerge from the
harness
> > somewhere else.
> >
> > >I cleaned the terminals to all the affected accessories
> >
> > Corroded terminals do not generally cause shorts, but they could have
been
> > touching something the was grounded before your fiddling. Again, not
> > likely to have exactly the same affect any two wires before and after.
> >
> > >and removed the voltage stabilizer (according to Moss, not supposed to
be
> > >one on the 67, but there was). I sanded the case of the stablilizer and
> > >where it mounts to create a better ground and lowered it where I could
> get
> > >to it the better the next time.
> >
> > That could (possibly) have accounted for a short to the body in one
green
> > wire at the prior mounting location, but probably not affecting two
wires.
> >
> > >This fixed (temporarily?) the problem, although I don't know which one
> was
> > >the direct cause since I didn't want to blow any more than the 5 fuses
> I'd
> > >already blown
> >
> > I have a sneaking suspicion that you have not seen the last of this
> > problem. Perhaps it's a bare wire that was cut on the edge of sheet
metal
> > where it pases through the firewall, and the short is disturbed
> > (temporarily) when you move the wire. If it happens again, start over
and
> > be sure you check the three different green wires individually for short
> to
> > ground (and not possibly checking the same one twice?). Meanwhile, keep
> > some more fuses handy.
> >
> > Barney Gaylord
> > 1958 MGA with an attitude
> > http://www,ntsource.com/~barneymg
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