project 1980 Austin Princess

[vulgalour]

Physically unplugged the lighter sockets, unplugged the hazard relay (this is separate to the indicator relay, since its on a different circuit to those), removed the interior light bulb.  That should disable those items, I'd expect.

[SiC]

Likely the electrons are escaping through a cable that's been chaffed or cut on that circuit. Given its blowing fuses instantly it must be a hard short to the body.

[PhilA]

Yeah. Problem is in the wiring between fuse and one of those things.

[vulgalour]

Horn is on a different circuit (and works as it should) and the boot light is effectively removed since the switch I've got is wrong for the boot rams I have fitted, so that's not been working for some time now.  Damaged wire shorting on something does seem plausible given the way this is behaving.

[JeeExEll]

^^ Fair enough if the horn is still working as it should with the problem-fuse out.

Another possibility is a short to earth at the fusebox right behind the fusebox itself - tiny scrap of metal, remnants of blown fuses, fuse terminal touching bare metal or a fixing screw, etc.

 

Good luck anyway.

[vulgalour]

That's a problem we've had before so yes, also likely.  I can still see me building a custom dash and loom for this car you know.  Not because it'll look better, just because it'll actually sodding work properly.

[PhilA]

No, live goes to the bulb, then from there to the switches. Ground the switches to bring the light on.

 

So, with the bulb pulled you're looking at the wiring all the way to the lamps.

 

Phil

[vulgalour]

er... okay?  Maybe I should clarify precisely what I did and you can educate me on how to disconnect the actual wires.

 

cigarette lighters - the wiring loom terminates in several plugs/connectors per lighter.  I disconnected these plugs from the lighters.

Interior light -  the circuit is completed with a festoon bulb.  I removed the bulb.  I could have unplugged the connecters that go into the housing but that seems a bit pointless if removing the bulb achieves the same goal.

Hazards - removed the hazard relay.

 

As I understand it, that's how you disconnect these items so I'm not sure how I'm supposed to disconnect the actual wires without, I dunno, chopping the loom?  Which I'm not about to do, obviously, unless that's part of the repair.

[vulgalour]

Let's do a bit of problem shooting on this then.  Disconnected the speedo cable at the gearbox end so that the cable could be drawn through into the cabin and prevent risking damage to the clip that locks it to the binnacle.

20180405-01 by Angyl Roper, on Flickr

 

Then disconnect the hazard relay, all the wiring to the dashboard itself, the rear cigarette lighter and the interior light wires.  Test the fuse holder and something is still drawing power.

20180405-02 by Angyl Roper, on Flickr

 

The only things it can be so far as I can figure out are:

Door switches - forgot to disconnect these

Fusebox - could be bad connections in the back of it, or something of that sort

Wiring loom - broken or chafed wire somewhere unseen

 

Next job is multimeter and disconnect the door switches to see if that solves the issue.  There's not really much wiring the problem can be in at this point, it's just a nuisance that the wiring it's likely to be in is difficult to get to without dismantling the interior.

[Des]

Is it possible there's been a historic fault, like someone stuffed a spoon in a faggy socket, and somewhere inside the loom the insulation took a melting and now some unrelated strands are rubbing shoulders. What about connecting a horn unit across the fuse and give anything you can get to a good prodding, flexing, a ripping and a tearing whilst listening for changes in tone?

[SiC]

Is the short still there with the dash off like that? I wouldn't have thought it was the door switches, as most almost always short to ground when the door is opened. I.e. they have one terminal to the light circuit and the other is the body. Easiest, simplest and cheapest way of doing it.

[Pillock]

I think what Ben is alluding to, is that if the wiring has a cut and is touching earth then disconnecting it from the fag lighter won't have any effect.

 

Battery --- fuse --- switch --- OMGCUT --- fag lighter -- ground

 

If electric is escaping at OMGCUT where it's chafing on something metal then anything after that is irrelevant, you're still getting a dead short which is blowing the fuse.

 

I guess you could, with the battery disconnected, see if any positives have low resistance to ground? You should be able to isolate it to a single wire at least that way.

 

Or an exorsism.

[JeeExEll]

Seat belt warning light switches, either at the seat-buckle-things themselves / or the wiring to them?

 

Depending on cable-route, possibly accidentally nicked a wire when screwing the console back in and a little bit of movement in use has the live feed now shorting to earth?

 

They're on the same fused circuit, fuse 5.

 

And the carpet's been out recently for recolouring.

 

Maybe??

[vulgalour]

Des: an historic fault seems likely, one that's been ignored or worked around somewhere.

 

SiC: yep, still shorting with the dash out.  At least I feel moderately confident it's not the dash causing the fault, so that's something.

 

Pillock:  that makes sense, though if it is a cut it's going to be difficult to find.  I wonder if this car met Junkman's P6 in the past?  Would explain a lot.

 

Jee: Seat belt warning light is on a different circuit and working as it ought so I don't think that's the fault.

 

Probably won't get to investigate this further today, errands and such have rather got away with me today and I haven't much time between now and work starting so might have to poke it tomorrow instead.

[vulgalour]

Bolting the dashboard back together gave me chance to have a little think and a look at what's what.  The run of wire that goes to the rear cigarette lighter does go by so brackets and stuff that could pinch the wire and short it out, to find out for certain I need to remove the passenger seat so I can lift the carpet, which is a job for another day.  The other thought is going back to early in my ownership when wiggling the fusebox would make the wipers work when they decided not to so it could be a fusebox issue.  I'm planning to replace the fusebox with a modern blade type anyway and I'm thinking that this might be a sensible upgrade now.

 

The one thing I do feel comfortable about is that the problem isn't in the dashboard and at least it's not a problem that prevents me from using the car, it's just a niggle at this point really.  Oh, and the multimeter didn't tell us anything we didn't already know without pulling the passenger seat out, as mentioned, so we need to get the Princess to the unit for the better diagnostic kit Mike has which will help us see a bit more clearly what's going on, I'm told.

[JeeExEll]

Don't immediately dismiss seatbelt-warning-light switches / wiring yet Vulg. (See page 75 in this thread, MikeKnight @12.01 - I thought we'd been here before!!).

 

Maybe see also handbrake warning-light switch, wherever it is (I don't know exactly but it could well be powered from the same fuse / part of the wiring loom via the contacts of an "operation-while-ignition-on-only" relay).

 

 

* Does anyone have a copy of a wiring diagram for a Wedge? *

I realise there's not much wiring in a car of this age but it would make fault-finding so much easier.

 

There's a pdf for late 70s MGBs on the net which I would expect to be similar but may be misleading.

Wiring diagrams for a Wedge don't seem to exist on the web.

 

Maybe they've never existed, ever.

Even at BL.

[vulgalour]

I've got a copy of the diagram.  Do I need to scan it and post it here?  Seatbelt and handbrake warning lights are on a separate circuit, both only work with ignition on.

[JeeExEll]

That could be useful Vulg if / when you can, and it lets others see it. Didn't know if you had one.

 

Am guessing but wiring for seatbelt & handbrake lights on these could still be overcurrent-protected by the same fuse 5, but run through two separate pairs of contacts of a relay - an electrically operated switch which only closes it's contacts when the ignition is on. Other circuits protected by the same fuse like hazard flashers are not run through an ignition relay and would have power available all the time.

 

But that is a guess. Mike obviously had reason to believe at that point a year ago that the seatbelt lights were protected by this fuse so it's worth checking out. Could be something really quick and simple to fix.

 

More Wedge info required.

[vulgalour]

I'd rather not cut and rejoin anything if I can help it.  Not a big deal to remove the seat and lift the carpet to check the wire in situ and repair/remove if needed.

[chodweaver]

If you say there is still a current draw with all the items disconnected (interior light bulbs removed, cigar lighter disconnected)... pull the fuse, remove the light bulb(s) and disconnect the cigar lighter. Put one probe of your meter on the positive supply at the cigar lighter's plug, the other to a known good earth - behind the dash or bodywork around the seat mounts, handbrake etc. Set the meter to measure resistance - if its showing OL - open circuit, then your problem is not on that wire. Move on to the interior light fitting - remove the bulb - one of the contacts will show a low resistance between it and earth when a door is open - the switch earths that contact to put the bulb on. The other contact of the bulb holder should show OL - if it does not, but shows a resistance of a couple of thousand ohms or less, your partial short to earth is on that wire. Trace the wire to find the bared, chafed or melted bit.

 

(Sorry, if I'm covering old ground.)

 

Sent from my BV6000 using Tapatalk

[vulgalour]

Ben and Chod:  That's what Mike suggested today, more or less.  It's just tedious diagnostics to find the problem now.  At least it's not self-healed, that would be my second least favourite outcome.

[JeeExEll]

Any progress Vulg?

[vulgalour]

Nope.  Today is the first one I've had off in at least 6 weeks so I went into involuntary shutdown mode and have mostly been slobbing about eating biscuits, drinking tea, and watching Russian dashcam vids all day.  It's been... nice?

 

Funny thing though, you know I mentioned about the electricity falling out when waiting at lights?  It did it again.  What's weird is the car _only_ does it at those lights and when I mentioned it to Mike we remembered another car (possibly the Corsa) did the same thing at the same junction.  Perhaps there's something in the area that's interfering with the older, more basic electrics?  Other than that it's been fine, I just haven't had the motivation today to do actual work like scanning wiring diagrams and fettling with wiring, even though I've had the time.

[jon928se]

Wish I had read this thread a bit sooner

 

I recall back in about 1980 - 1982, old man had a 2200 Princess then a 2000 O series, mates dad had a 1700 then 2000 O series All owned from new apart from the 2200. IIRC the oldest one would not have been more than 4 years old when replaced. All of them developed the earth through the accelerator cable condition, one spectacularly so when jump starting it and the cable sheath burst into flames. All cured by replacing the battery earth cable.

 

I learnt to drive in the 2200 and did approx 8000 miles on L plates waiting for a test - 9 months after my 17th birthday, including towing sailing dinghies and driving down to the south of france on holidays. Great motorway cars - the lack of PS contributing to astonishing accuracy at speed.

[purplebargeken]

Just sat here and thought wonder if it is the fusebox itself and that upgrading to a modern one might help. I then scrolled through the more recent posts and saw that was your plan anyway. Now I feel stupid.

[vulgalour]

Don't feel stupid, Ken, it's just a case of great minds thinking alike.

[PhilA]

It's unlikely to be the hand brake warning light circuit. If you had a break under the carpet for that and the wires were touching the body all you'd get would be the warning light on all the time on the dash. That works in the same way as the interior light.

 

Battery - fuse - bulb -------------- switch - body (ground)

 

The longest run of likely pinchable wire on those will just illuminate the bulb and not cause it to pop the fuse.

 

I would start looking at the circuits that don't do light bulb type things first and work backwards towards the fuse.

 

Phil

[JeeExEll]

^ Yes, but remember any live cable coming from fuse 5, or spurred from it, could be shorting to earth (and popping the fuse) at some point BEFORE it actually gets to wherever it's meant to be going.

Regardless of what it's function is.

It will pop the fuse with nothing switched on.

 

At least we have a definite fault at the moment rather than an intermittent one, although that benefit can be lost if things get moved and disturbed. Then the fault might 'go away' for a while. Waiting for the most awkward time to reappear.

[Mally]

Ben's not as stupid as he sometimes tries to be 

[vulgalour]

Had a bit of time today to have a look at this, literally have a look because the multimeter isn't at home and my next free time is Tuesday.  Doesn't do any harm to look for physical damage to the wiring at least, could even tip off where the issue is hiding.  First up, the physical route of the wiring to the rear cigarette lighter.  I'm using the forum uploader because Flickr is currently playing silly buggers.

 

Start behind that dash where it drops down under the carpet.

 

 

This then runs under some heat/soundproof foam with a small tail off to the reverse light switch and ground point.

 

 

After that, it goes under the rear half of the carpet and has tails for the handbrake switch, seatbelt stalks  and passenger seat (warning light on dash operated by switch in seat), and finally to the rear cigarette lighter.

 

 

A physical inspection reveals nothing amiss.  No burning, chafed wires, problems with pierced wiring or trim fixings, nothing pinched.  There's no obvious problem here.  I can't inspect the loom where it goes up into the dashboard without removing the dashboard again which I'm not willing to do today.  The problem remains, of course, as I've not actually fixed anything.  However, even wiggling the wiring around, and isolating the plugs on the wiring loom from anything they might earth on, the problem remains which probably means the issue is somewhere between the dashboard and fusebox.

 

More and more I'm thinking this is a fusebox related issue to be honest.  I did lever the fusebox out of its spot and again there's no obvious signs of any real damage there.  Next step will be to head over to the unit on Tuesday and get the dashboard out again and get the multimeter to work on the loom.  This is a particularly odd problem to me because it's manifested when nothing was repaired, changed or worked on, it's just something that's started happening.  If it had started when I'd, for example, fitted new horns, it would be much easier to grasp what might be at fault.

 

Finally, the wiring diagram I have to work with which, if I'm honest, I do struggle to understand.  If anyone that can read these would like a larger version, I can provide that on request, hopefully this is large enough to view on your screen of choice.