Testing for grounding?

[Allan NZ P5b]

Is this right?
It was explained to me that if you disconnect the negative earth and attach the red positive lead of a digital volt meter to this earth and connect the negative lead to the battery negative terminal and the meter shows 12 volts then you have a grounding somewhere on the circuit and by pulling fuses you can identify the offending circuit. When I draw a diagram it makes logical sense to me. Is this correct or am I missing something?
If this were the case why would I get a reading of 1 volt? Even when the clock is disconnected? (To test).
When the courtesy lights are off what else beside the clock if anything draws power when the car is idle?
I have not yet pulled the no 1 fuse and tested again.
Oh voltmeter reads fine on a full circuit

[Phil Nottingham]

What do you mean by "at idle" the coil, the inhibitor switch and Alternator field isolating relay all draw current when igniition is "ON" or engine running

If you mean stationery and switched off then it could signify stuck contacts in the field isolating relay or even hidden faulty insulation/bullet connectors.

Is your wiring loom the old type textile covered mixture fitted to early P5B's

[Allan NZ P5b]

"when the car is idle?" not at idle.
ie just sitting ther. shut down as if you were to lock it up and go inside for the night.
Not idling as in engine running bad choice of words in retrospect. should have said " stationary, engine off, ignition off & with all systems shut down"

[Allan NZ P5b]

Tom is usually good on wiring. Why the 1 volt reading and is my approach sound?
How do I test field isolating relay?
I did have a good auto sparky check alternator and charging circuits would this have included the field isolating relay. As they all came up fine. Where is the relay as on modern alternators they are part of the alternator assembly are they not? Art they mounted separately on a p5b

[dorsetflyer]

Alan at the top of the picture on the right you will see the fuse panel. Next to this is the 4TR alternator output control unit, can be either red or black. The silver can next to it is the warning light control unit (3AW). Above this is the alternator field isolating relay (6RA).

Modern alternators have all these items usually incorporated within them so only two or three wires exit the alternator itself.

Some members have changed the old style alternator, and fitted one from the Ford Orion which gives more output, and makes the three items redundant.

Hope this helps.

[Phil Nottingham]

;)The field isolating relay just relieves the ignition switch of some load. After noting the connections just remove them all and then do your test - its a standard on/off single pole relay and modern equivalents work just as well.

It is fed direct to the battery (onto the starter motor)so be careful where you rest the leads.

If your meter is reliable there is an earth short somewhere so elimination/substitution is the quickest way to find it

[Allan NZ P5b]

Thanks for all the help will perform tests this weekend and report back. ;D
Also while doing this I will try to put in the (new to me) coupe gauges ;D
See earlier thread.
Would also like to wire in relays for Headlamps at this time, in preparation for latter halogen upgrade.
See new thread help required