RE: [doc] Re: Wiring Harness

[Nick Tomlinson <nickandkathryntomlinson@xxxx>]

To John,
 
I agree with Rich. When measuring voltages I assume that you have connectedthe black lead on your meter to the -ve post on the battery. If you connect this to some other "wire" then all the meter does is measure the voltage differential between the meters cables. I always use the -ve battery post as an ultimate datum for voltage reference. Continuity tests are not always conclusive as a short in the loom can always cause a short/ leak into another circuit, hence my suggestion for a true ground is a test wire between the battery -ve post and the binnacle earth/ ground point and to perform tests with all relays disconnected to isolate circuitry.
 
The trouble with a problem like this it is probably easier to test than write in the news group, we can only give pointers from not being able to testthe car.
 
Best of luck anyway.
 
Nick.

Richard <dickyh11@xxxx> wrote:
If you can detect *ANY* voltage AT ALL between chassis ground and the
'ground' at the binnacle or any other ground wires for that matter then
you _still_ have a floating ground line (in other words they aren't
connected to ground at all).

Testing continuity on this wire *will not* help since your tester is
just measuring a path to earth through some other device.

As I said before, the only to find out whether the binnacle wire: a)is a
ground wire and b) if it's actually connected, is to trace this wire *by
hand*, continuity testing is not going to help.

It's a pain in the arse, but a lot quicker than poking and prodding ad
infinitum.

Rich H


-----Original Message-----
From: jchapelhow [mailto:chapelhow@xxxx] 
Sent: 28 September 2003 2:54 PM
To: doc-uk@xxxxxxxxxxxxxxx
Subject: [doc] Re: Wiring Harness

All.

Many thanks for your continued assistance, I have received several e-
mails of suggestions off-list and thought it was time for an update.

To recap, my electrical problems are that several of the gauges 
fluctuate with differing electrical loads, ie the turn indicators 
cause a `bounce' in the oil pressure reading. The central console and 
door lock warning indicators also dim when the indicators are used.

I have removed the instrument binnacle and cleaned all of the 
contacts, several of the bulbs were not fully seated therefore 
disrupting electrical pathways. At the moment the binnacle is still 
removed. 

I have temporarily unplugged all of the wiring connectors at the back 
right of the engine bay. The buzzer logic box panel has been removed, 
along with the intermittent wiper module, leaving just the flasher 
relay to `dangle' under the dash.

I have run a temporary ground connection from the engine bay ground 
point to the individual wires grouped near the left front wheel.

Now when I test the earth points either at the binnacle connector 
blocks or at the dashboard end of the buzzer box ground I am able to 
detect a voltage when circuits are turned on (0.7v side lights, 1.2v 
main lights, fluctuates to 1.45v when indicators are used), 
continuity tests also fail as soon as the ignition switch is moved to 
P1. Is this what everyone refers to as a floating earth? 

All new relays/fuses have been fitted (with all the connectors 
cleaned), the connectors to the ground by the front wheel look good 
and measure low resistance until `something' is energised by turning 
the key. This even happens with fuse 12 removed, the courtesy 
circuits (door lights) also seem to place a voltage on the ground 
cables.

All ideas welcomed.


John Chapelhow
DOC 19 : MMG 287W : `Boeing' 0737







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