Ruby's electric problems

[Denis Sweeney]

Trying to sort out Ruby's electric's problems I have started by removing the Lucas PLC2 Ignition switch from the dash so it is now out on the kitchen table.
Not being a sparky, I searched the forum for help and found a technical paper published by the Cornwall A7 group, this gave details of testing the PLC2 switch for faults.
I hope I have followed each of the tests in order as presented in the technical paper using a circuit tester to check the switch and detail the results below:
 
No circuit is indicated between A & D with the ignition either switched on or off.
No circuit is indicated between A & D with the light switch in all four position, 1, 2, Side or Head. This was also checked with the ignition in both on and off positions.
With the light switch at position 1 no circuit is indicated between D & F1 or D & F2.  
With the light switch in position 2 & Side a circuit is indicated between D & F1 but no circuit is indicated D & F2.  
With the light switch in position Head there is no circuit indicated between D & F1 but there is a circuit between D & F2.
With the light switch position 1 & 2 no circuit is indicated between A, T & H.
With the light switch in position Side there is a circuit between A & T but no circuit between A & H.
With the light switch in position Head there is a circuit between A & T, A & H and T & H.
With the ignition switched on there is a circuit between the IG terminal and the centre A terminal.

I believe that this is all the tests that the technical paper listed and I think it indicates that my ignition switch would be sound ?? ........or not ??

However when we were about to leave, I know that when I turned the ignition on the fuel gauge did not always come on and more disturbingly the fuel gauge did move when the light switch was operated, is this a switch or an earthing issue ??

If anyone can shed any additional advice it would be gratefully received.

I will now start checking all the wiring on the indicator circuit including all the earthing circuits, probably not until early next week.

Cheers for now
Denis S

[John Cornforth]

Hi Denis

I attach diagrams of the four positions of the PLC2 switch, showing what is happening internally in each position of the outer lighting/charging section.
  PLC2 Switch 1.jpg (Size: 73.98 KB / Downloads: 417)
  PLC2 Switch 2.jpg (Size: 74 KB / Downloads: 417)

The fuel gauge runs from the Auxiliary Fuse, which is fed from the output of the central ignition switch via a white wire.  This same terminal feeds the live side of the ignition coil via another white wire.  The fuel gauge thus only comes on when the key is turned in the ignition switch, it should not be affected by the position of the lighting/charging outer switch.

If turning on the headlamps produces a change in fuel gauge behaviour, it's a sign that the earthing from body/chassis back to the battery is not fully effective.  If there is no separate earth strap for this purpose I suggest you fit one.  It's not a good idea to rely on incidental earths via the copper petrol pipe and oil pressure gauge pipe as these are not reliable.

See my re-drawn wiring diagram here:  http://www.da7c.co.uk/technical_torque_a...4%20A4.pdf

[Denis Sweeney]

Thanks John, I have not been able to have a look at Ruby today, garage too small to work in and it was pouring today, flaming June!!

I have attached a word document with a some pics of my wiring and a couple of questions, any advice/comments as ever, would be much appreciated.

Cheers to all Denis S

[John Cornforth]

Hi Denis

I've had a brief look at your document. You seem to have the earthing covered. I will take a more detailed look in the next day or two. I am tied up today sorting out the brakes on an Aston Martin and an unreliable starter motor on a Bentley. Fortunately the owner of these has a large well lit garage and his wife bakes lovely cakes !

[Bob Kneale]

Hi Denis
Haven't forgotten you or the problems with the ruby electrics.
The one area we haven't looked at is the Fuse box area where the auxiliary fuse connections are located.
If the component is corroded underneath the connections between the live feed and the other end may be badly corroded.
As a  temporary measure try shorting out the fuse connections, and see if it has any effect.
Since we are clutching at straws...............
Cheers Bob

[Denis Sweeney]

Thanks John, ………. cake or electrics, no contest!!

Will check that out Bob, weather here dry and hopefully have a full day to go searching, no cake tho’

[John Cornforth]

Hi again Denis

I have now had a chance to take a more detailed look.

Your problems seem to centre on an erratic fuel gauge. This is supplied from the auxiliary 25 amp fuse, along with the stop lamp and the indicator switch common point. The gauge also has a connection to ground via the cutout ground, and a connection to the tank sender. The return from the tank (originally rubber mounted) is via the copper petrol pipe to the petrol pump and thence the engine block.

Some questions:
Is the auxiliary fuse and its holder clean and tight ?
Is the copper petrol pump intact all the way to the petrol pump, i.e. no sections of rubber hose, plasic filters etc ?
Is the ground wire from the E terminal of the cutout present and working effectively ?
Is the stop lamp grounded effectively to the bodywork, i.e. does it have a dedicated wire and not relying on contact from the boot lid to the body ?

As you can see, I still feel that interaction between gauge and lighting is related to a poor ground somewhere. It may be prudent to remove ground connections and check there isn't paint or corrosion underneath.

Some other observations which are probably unrelated:

The original starter wiring has two thick cables directly from the starter motor (live stud and grounded fixing bolt) to the battery. Do you still have both of these, or has the ground side been replaced by the one to the cylinder head via the battery box ?

Capacitor type suppressors should not have their live wire lengthened beyond the supplied few inches, as this reduces their effectiveness. In my experience, HT plug top suppressors (5 kilohms) are much more effective at preventing misbehaviour of electronic flashers, it is the interference radiated form the HT leads that is dominant.

[Bob Kneale]

Hi Denis
I forgot to add last night, that the stud on the back of the fuel gauge that screws onto the metal saddle that  physically secures the instrument to the dash needs to be properly boned to earth. There are actually TWO coils in the fuel gauge; one which is responsible for measuring the amount of fuel in the tank, and the other which is there to compensate for voltage variations in the  dynamo.The battery voltage is higher than the nominal 6 volts when it is being charged.
Although the purists don't like them, your choice of using spade connectors makes maintenance and fault finding so very much easier.
Good luck in your continuing quest and best regards to Vicky. I shall be sending a PM 'Dreckly'
Cheers
Bob

[Denis Sweeney]

Thanks John and Bob for all your comments and advice, far too long a story to bore you all with but Ruby is back up and running again, the cause of the problem was as you both correctly predicted, a failed earth connection.
Briefly, where I had added the suppressor at the earth point next to the coil, my poor crimping of the connector had failed and so lost the earth connection which then caused all the other issues.

A lesson learned.

Cheers and thanks again
Denis S

[John Cornforth]

Hi Denis

Very glad you have got this one tracked down

Personally, I am not a fan of crimp connectors for the home workshop. They are fine if you have the correct professional grade crimp tool but that's an investment few will make unless they do a lot of work on cars. I prefer to make a good solder joint on clean components, then supplement this with heat shrink sleeving and loom support to remove any vibration stress from the joint.