earth fault in cabin wiring harness or instruments, etc

[Valcuda]

Further to my two previous posts, I now discover the electrical problem is more serious than I thought. Please excuse the length of the following post.

During a series of circuit testing checks, working backwards, I've discovered that with the earth strap removed from the battery, the live lead from the battery in the engine bay has a resistance to earth even though the headlamp switch is off, the ignition is off, all other switches are off and the doors are shut (so no door switch activity). There are no accessories--I've removed the clock I added and the leads are just hanging clear and loose.

(The measured resistance is 8ohms one way and 50Kohms with the meter leads reversed, but I know there aren't any diodes in the circuit so that's a red herring).

I separated the live lead from the fusible link and there was no fault so I reconnected the link.Clearly there's an earth fault somewhere beyond the bulkhead, in the cabin. (The rear lights and reversing lamp are switch-controlled from inside the cabin).

It could be the headlamp switch. By contorting myself I can access it from underneath (I can press the release button OK) so I can remove it from the instrument panel but will it dangle down sufficiently to be able to fiddle with its spade terminals? (I can remove the lead to the headlamp spade B1, for instance and see if the earth fault of the live lead from the battery goes away). If the cables are too short for the switch to dangle down, I'll have to remove the instrument cluster. If the switch is OK, I'll have to remove the cluster anyway.

The service manual says that to remove the cluster I first have to drop the steering wheel column if it's a Valiant but it doesn't say anything about this if it's a Barracuda. Since my car is a hybrid, a Barracuda with a RHD Valiant-type cluster, can anybody advise if I have to lower the steering column or not? Is it easy?

I'm working in a confined space (single garage) so I'm trying to plan ahead for minimum disruption.

It's possible the fault has been there for some time. With a battery cut-out switch used when the car is garaged, the alternator might have been supplying enough to keep the battery charged as well as feeding the fault!

Any help or advice on the above points would be greatly appreciated. Thanks guys.

[Rebel]

Not sure if your steering column will be the same as mine ( 68 charger ), but if it is, it's easy to drop the column.
I've attached some pics of where the bolts / nuts are that need removing.
The ones circled in red are under the column, just where it goes under the dashboard, those circled in yellow are next to them. The one circled in blue is near the bottom of column up under the dash and the most awkward one to get too. The final two are at the bottom of the column where it goes through the bulkhead.

Hope this helps

[Rebel]

Don't remove the two under the dash ( circled in yellow ) altogether until you're ready to drop the column. That way it won't fall on you

[Dave999]

ok with the ignition off

the only things still live that doesn't go through the portion of the fuse box fed by the ignition switch

are likely to be

ciggy lighter

interior dome light (other courtesy lights)


a short in either will easily melt the insulation and cause a bigger short.

for dome light use old cable to pull through new if you need to re wire

and make sure the light back and connectors are insulated from the inside of the roof panel

OR

try it with the alternator disconnected at the main battery stud on its rear

if the resistance looks infinite with the alternator disconnected I suspect that 1 out of the 4 diodes in your alternator has gone.

4 in there. easy found at maplin get the fattest you can solder them in with the lines in the same orientation.

keep in mind that the engine will happily earth through the water in the radiator and through the throttle cable or metal fuel pipe.


what is causing you to think there is an issue?

did the battery go flat?

are you running a mechanical or solid state voltage regulator? if the points in the regulator seize it can stay on.

obvious if you try to turn alternator by hand with the belt off. dead stiff? its still on or the bearings have seized.



A body column with manual 4 on the floor or floor shifted auto

4 bolts into a plate on the bulkhead

undo a few turns no need to take out

2 bolts on a bracket welded to the tube under dash

take both out

column should drop down a few inches

more if you undo the nuts at the bottom more

put in key

undo steering lock

then either twist column round so indcicator stalk points to floor getting the bits in the way of dash removal out of the way

or just let it flap

depends on your dash.

if you have a 3 speed steering column mounted shifter. I don't know how complicated this could be. I can more or less guarantee that you can't just. twist the column casing round or flop the column down a bit without straining the shifter linkage.

PS my manual says remove column to take out dash pod

I have never had to remove the column or even lower the column to take out dash pod. but mine is a very different car.

I did have to use a screw drive with a right angle bend in it.


Dave

[Pete]

Great posts and very helpful, guys!

[Valcuda]

Hi Dave, thanks very much indeed for your helpful step-by-step testing procedure.

What caused me to think there was an issue?

Now that I've laid the car up in the garage for the winter, I thought I'd fix the after-market clock I'd installed twenty years ago which stopped working a while back. It was added to the cigar lighter lead. This was meant to be just a quick afternoon job, check there was power at the splice, check the clock against the battery, fit it all together again!!

While checking which leads came from which fuse in the fusebox (doubled up like a hedgehog with the multimeter in the drivers footwell), one thing led to another and I discovered the panel lights weren't working when I put the headlamps on--simple test of whether I'd reconnected the battery earth strap or not. The fuse was fine so I got diverted from the original project (hence my first post about the headlamp switch). I spent an hour drawing out the headlamp/fusebox circuit, adapted from the wiring diagram in the 1969 manual. Then, when I was round the engine bay while the battery earth strap was disconnected, because the multimeter was in my hand, I did the resistance test on the live lead for no particular reason. I got the readings I quoted and thought, this surely isn't right. I had no premonition of any fault here. That's how this latest post came to be.

Your mention of alternator diodes could explain the two totally different resistance readings I got. I may be panicking for nothing!!!! I will get back to the car this afternoon and follow through your procedure.

I will definitely report back.

[Valcuda]

Panic over.

I disconnected the alternator lead and got infinite resistance both ways round. So it was the alternator diodes I was detecting. I hadn't expected the diode resistance to be less than infinite (though 50K is pretty large) in the reverse direction and that's what threw me. Thanks, Dave, for steering me in the right direction.

(If the alternator does start playing up, as a first course of action, I've got a spare from Martin Creber's old Barracuda that I bought for spares some years ago before going down the "diodes from Maplins" route.)

I sorted out the panel lights by feeding them from the sidelight (parking light) lead, thereby bypassing the headlamp switch rheostat.

So all's well now.