Earthing problem within the cab

[an_avenger]

Hello - I was stuck in afternoon rush-hour traffic today but being quite happy inside my warm and cosy cab I thought nothing would go wrong......BUT whilst struck in the traffic I noticed my fuel gauge registered 'empty' - worried I thought I would break down here (a not popular spot to break down in the best of times) but immediately I remembered she has a full tank.... Bored and bemused I flicked the indicator (but it didin't work), I tried the horn, interior light, heater and winscreen wipers but they all seemed to not work.

Occasionally the heater flicked on and off on it's own accord (obviously when the sitch is turned on) but it was more frustrating than a hazard. The head lights and fuel pump worked fine, no problems in the engine either....It's just the luxury goodies inside the car which seem to not work. Is this a common problem and what should I look for in regards to earthing problems? It must be something loose if, occasionally I get back the power to this accessories. Are they on a common earth line?

Please help my right arm.........I don't want it to freeze off when giving a hand indication....!!!!!

[rtbarton]

Sounds like a fuse problem. The clips that hold the glass fuses in place are notorious for intermittent connections.

[Cam]

There is an earth point inside the cab for the interior goodies.

It is located behind the driver's glovebox and fixes in place via the main bolt/screw the holds the steering column up onto the dashboard. It is the left bolt. check this to see if it is a bit loose, if it is, then that's your problem!! There is a nut on the other end which clamps an electrical eyelet to the body.

There may be other earth points within the cab but I have not come across any.

The lights are earthed via the inner wings and the other engine electrics, either via the engine earth straps, or the bulkhead.

[rtbarton]

If that earth is iffy the indicators should still work (but perhaps not the tell-tale) as they earth at the lampholders. A faulty live (fuse problem) will stop them from working though. I have had this problem on my Landrover, luckily I can twiddle the fuses from the driving seat.

[Willie]

This is interesting.....the items which failed are ALL supplied
through the fuses but not through the same one! As stated the
fuses often go 'open circuit' and need to be agitated in their
holders or removed and cleaned but not usually both at the
same time. I would suggest that CAM is right about the
common earth point under the dash near the steering column.
The way to prove if it IS this bad common earth is to see if
the STOP LIGHTS still work while the fault is present. (these
are the only items fed by the same supply which have a
different earth return) If they work then there is no problem
with the fuses.
Willie

[rtbarton]

But surely the interior light is earthed by its fixing screws?

My money (if I had any) is still on iffy fuses, perhaps the symptoms haven't been described accurately? I'm not trying to be funny but with over 30 years experience fault-finding on electrical/electronic circuits I believe nothing till I see it - and then not always

[Willie]

Well, if his stop lights do still work whilst the fault is present
it would prove the "bad common earth" theory because the
stop lightS are supplied THROUGH THE SAME FUSE which also supplies
the heater switch,flasher unit, interior light etc etc.
Willie

[rtbarton]

True - so are the indicator lights, but as I said they earth through the wings, so if they don't work we are back to the fuse, or multiple faulty earths.

And the interior light? where is that earthed? Is that fed through the ignition fuse? I'm sure mine came on when I opened the door or operated it's own switch even with the engine off.

I assume the engine keeps running under the fault conditions........

Also assume that no-one has modified the wiring, something that happens a lot on old cars.

There's more to this than meets the eye.

[Willie]

If you read the first posting re this problem it says what
did and didnt work. Engine ok etc...the items which worked
were all earthed at some point OTHER than under the
dashboard...thats why it seems the likely trouble spot.
I hope we get some feedback, it only takes a few minutes
to check the multiple earth tag.( I have no idea where the
interior lamp is earthed as I have a convertible)!!!
Willie

[rtbarton]

Faulty Items

Ignition fuse
Fuel gauge - Earthed at the tank - is there a regualtor fitted?
Indicators - Earthed at the wings - or was it just the tell-tale?
Heater
Wipers

Not fused
Horn - Earthed through the column?
Interior Light - Earthed at its fixings?


OK Items
Lights - not fused? OR fused via in-line fuse
Fuel Pump - Not fused
Ignition - not fused


We still don't know if the brakelights work, what about the panel lights?

[Willie]

You do not seem to have access to a wiring diagram??
the horn and interior light ARE fused. The ignition circuit
certainly isn't, for safety reasons. As you say we need to know
if the stop lights work when the fault is present.
Come on AN-AVENGER how are you doing????
Willie

[rtbarton]

That's true - I'm going from memory and could easily be confusing with other Nuffield/BMC cars I've owned.

My mistake saying the interior light isn't fused - it is.

The reason some cars didn't fuse the horn(s) through the ACC fuse is that they take a lot of current so the large fuse required would not protect the Accessories wiring, unless you used heavier than necessary wiring.

I guess the Moggy takes its horn supply from the A2 terminal?

[an_avenger]

well I've tweeked a few wires of various colours. Yesterday the dash and glove covers came off so I could access the wires. Apart from breathing in years of dust there were no wires which were loose or frayed or touching the body

I've overhauled the fuse box (it's clean and all contacts are shiney with 'tin' coatings by using a soldering iron). All essential systems are working at the moment (fuel gauge, lights and indicators), the heater works fine now. It must have been a loose connection 'somewhere' but at least the fuses are clean and have good contacts. Thanks for the advice guys...... I'm sure the heater is a bit iffy so when it's not fully required in summer, I think overhaul time. But I've copied the forum into word so if the something similar happens again I'll refer to it.

Brrrrr it's cold