Electrical gremlins

[PedigreeChummy]

Hi gents.
First post on here for what seems like an eternity... must be a sign that everything has been running well, UNTIL...

Took the dash panel off to check if there was some minor blockage in the oil pressure line to the gauge, as only tapping it over the past 6 months has caused it to work... now wishing i hadn't as there were two wires seemingly unconnected to anything that were badly insulated behind the dash,remnants of electrical tape on them. They touched and something shorted.

Now i have no dash panel instruments working, no ammeter reading, no running lights at all, fuel pump isn't kicking in when I turn the ignition key, no horn etc., however the starter motor is turning over at full strength, rotor arm turning in the distributor and points opening and closing correctly but no spark. 6v to everything as normal, including fuel pump, coil, the whole shebang, no fuses blown in the CFR (tried them with new ones just in case...). What am I missing? The dark arts of electrics not my forte.

1932 Tourer, for what it's worth...

Help!

[Bob Kneale]

Just a thought but is the feed from the starter motor to the ammeter connected again, or the connection from the ammeter to the switch connected. I'll think more deeply about the problem during the afternoon.
Good luck
Bob

[PedigreeChummy]

Thanks Bob.

Yes everything connected as before. I haven't disconnected any wiring at all, just the oil pressure pipe to that gauge.

The two errant wires didn't seem to have worked loose from anything, and indeed they both have ring terminal connectors on them, so could have pulled out of anywhere with me removing the instrument panel. This is the first time I've had it off, and everything has been fine until these two wires brushed together... tracing them will be a bit of a pig, as they are taped tightly into the rest of the the loom, and unfortunately they aren't differentiated by colour.

[John Cornforth]

Hi Pedigree

The starter motor current is about the only thing that doesn't go through the ammeter, so you would appear to have lost the main supply to the car electrics at or near the ammeter.

My suspicion is that the two ring terminals were for an ammeter of the type that has screw terminals. This may have been replaced by the alternative type that has just one or two turns of insulated wire on the back (The needle responds to the magnetic field of the current in the cable). If my hunch is correct, the two terminals should be joined together. Bit surprised they weren't bolted together and taped rather than just taped. What colour are the wires ?

However, to be on the safe side, I recommend doing some ohmmeter checks with things all switched off and the battery disconnected, to determine for sure where those wires connect. Spare ends weren't a feature of the original wiring !

One last thought which is probably not relevant but I will include just in case. If you don't have a dedicated earth connection from the engine block to the body/chassis, electric current can find its way to or from the engine down the copper oil pressure tube and via the oil gauge to the dash metalwork and thence to the body. However, this would only affect things like lights that earth to the body and not the ignition that earths to the engine block.

[PedigreeChummy]

Hi John, thanks for the input.

It could be that the two wires were taped together but would that account for them shorting? Unless maybe one of them had brushed against another connection on its way free...

Is it possible that I have fried the ignition switch, as it seems that everything that doesn't work is running through that, and everything that is working, doesn't? Are they even "fry-able"? Or maybe the CFR?

[John Cornforth]

Hi

For a standard Ruby (your 1932 A7 will be very similar), the ignition switch (spade/key switch) part of the PLC2 controls:

Ignition coil
Ignition warning lamp
25 Amp fuse which runs the Petrol Gauge, Stop Lamp and Trafficators

With modified wiring, it's anyone's guess what else has been added to this switches workload !

These switches are fairly "chunky" inside, and resistant to overload but maybe a long term direct short of the battery could have affected it. With 90 years of wear, they can sometimes get a little unreliable.

The CFR is also pretty robust

I can only suggest that you get out the test meter and start probing

Apologies for anyone tired of hearing about it but see my Ruby wiring diagram here: http://www.da7c.co.uk/technical_torque_a...rubies.htm

["Slack Alice" Simon]

"I haven't disconnected anything, only the oil pressure pipe ....."

What if it was being used as the earth return from dash to engine?

[PedigreeChummy]

Yes, good point, Simon, one also suggested by John.

Tbh I didn't know that the oil pipe was used as an earth to the engine, but reconnecting it has made no difference to the symptoms, so I'll have to bite the bullet and start doing some tests.....

[k8207418]

Is there any voltage on either of the cables that were loose 

Just check between a good earth and each cable separately 

Also check if either of the cables are connected directly to earth using a continuity tester

[John Cornforth]

Hi

Just to be clear, the oil pipe isn't supposed to be the only earth, but may become so if the "proper" earth is bad or missing.

I remember a 1950's car I was called upon to sort out. The main starter cable had a poor connection, so most of the starter current was trying to go down the oil pipe instead. It got pretty hot !