Morris Minor Owners Club

I'm sure I am missing something here but would welcome any thoughts from any sparkys on the forum Short summary:

Restoration of '59 convertible - fit brand new wiring loom and rear off side lamp unit from well known parts supplier (late type). Car on road for three weeks in all weather conditions - day and night. Lights, heater and wipers on at same time regularly. All electrical systems operating fine no problems. Week on MMOC MOT 2013 no problems, everything working fine. Head to Switzerland/Italy for extra week of holiday and show at British Marques Car Show in Nantua, near Geneva - no problems. Head up Furka and Simplon passes - no problem. Descending Simplon Pass - lose brake lights and indicators. Fuse blown, replace fuse, check for any obvious issues, can't fix brake lights or indicators so decide to carry on and use tail lights as brake lights until I can stop to investigate issues. Ten/fifteen minutes later, lots of smoke in cabin and boot - wiring to rear lights fried and very small fire in boot which extinguishes very quickly. OK should have investigeted cause of original issues rather than carry on but hey! Car recovered back to UK. New loom needed and purchased. New loom fitted. All circuits seem OK but on testing lights rear o/s light very dim - thinks poor earth. Fiddle with wires and light goes brighter but now VERY hot and starting to melt. Circuit fuse does not blow - still intact. Switch off lights and disconnect battery - investigate wiring to rear light - now also melted and fused with other wires in the loom. Damage also to no. plate light wires and some evidence that wire to light switch is also damaged. New loom with power for no more than 2 minutes now toast Investigate rear lamp unit as possible cause and upon releasing mounting bolts water begins to leak from inside the light unit - eventually about quarter of a small plastic cup of water emerges. Remove light unit - tide mark where water has sat since June covering earth connection and reaching to just below the stop/tail lamp bulb holder. Cause of water inlet likely to be the garages failure to properly block up unused mounting holes for new light unit (which, for some reason, didn't seem to fit the original holes). No damage at all to sub-loom taking power to n/s light unit which appeared to work OK. All three earth points in the boot are secure and contacting clean metal. All other circuits seemed to be working OK.

OK question is - before I get to fit a third loom! Is the cause of the continual short and melting of the loom down solely to the water in the light unit creating problems or is it possible that it could be something else? Switch? Fuse Box? wary of blaming the smoking gun (or smoking light unit!!) and missing something else.

Before I fit a third loom I will run some wires from the switch and power source to light unit outside of the loom to replicate the rear lighting circuit to see if I can solve the problem but would welcome any thoughts from members as to other things that could have caused this issue.

Cheers

first thoughts is a short on the power side, rather than bad earth,wire chaffed ?,the start of the fire position gives a clue to where to look first .

Why did the fuse not blow? What value fuse do you have in the holder? And why a complete loom each time - surely just the rear section needed? I can't see a bit of water causing the problem - it's only 12 volts after all......

without going to look at mine,dosen't the loom enter the boot on the offside at the front,then go to the lights via a hole each side at the rear. Is there a grommet in all of these holes,thats where I would be looking first.Has to be a short to earth and that would be the favorite spots to check, Dismiss the water issue,all that would do is corrode the earthing in that unit shouldn't give enough heat to melt the loom.

No fuses originally in the lighting circuit for a 1959, so any 'shorting' problems can cause severe heating and loom problems. There are for both brake lights and if fitted, there should also be for the flashing indicators. If the loom has fried, I would look at the lighting circuit first.

Your idea of testing the rear lights independently of the loom is a good way to go.

Do you have a battery charger? Preferably one with a circuit breaker and not a fuse? If you have, use this as your power supply to check all connections. Unless it is a very high output charger, it cannot burn out the loom.

If not, then I would suggest to connect the battery end, and make sure that the connected wire cannot short out. Then touch the wire on the light connection. You may get a small spark, but anything else suggests a potential short.

Do one connection at a time!

Thanks guys - pretty much what I thought so pleased I am least on the right page. Roy - first loom burnt out completely back to the switch - the wires had lost all of their insulation and the connection to the switch behind the dash was crispy. When I stripped back the old loom, all the wires in the main bunch coming out of the bulkhead were fused together. Second loom is probably not quite as bad but there are signs that the damage to the wires in the boot, which have fused again, have worked their way up to the switch. The insulation on one wire has started to deform so almost certainly some damage to wires elsewhere in the main loom and where it splits to go rearwards. Not sure I would have the required peace of mind if I simply replaced the obviously damaged rear loom portion. Any future electrical/wiring problem might well be the result of damage caused by this incident and there would be no way I could check that if I still use the (possibly) damaged loom. Will probably get a mobile sparky to confirm the old loom is OK once I have nailed this lighting problem and replaced the rear loom. If all is OK after that then fine, if not then I will at least know the initial problem has been solved.

Idea of using the battery charger as the power source is one I had not thought of before. It has its own circuit breaker so will try that method. Grommets are present on all holes where wires emerge (boot floor and both inner rear wings), and the appropriate gasket present on number plate lamp too. Fuse in the holder is 10 amp. Can't start my investigations until next weekend but will then begin trying to sort out this annoying problem.

Ah right - missed the 1959 bit. I would URGENTLY fit a fuse in the feed from the light switch to the side lights....... And yes - lack of grommets could well be a cause. But the brake lights etc were the first to go...and that should have blown the main fuse - that could only have happened with a short to earth. You then used the side lights as 'brake lights' -which of course (if unfused) would continue the short - and the heating effect!

Don't disagree with anything gone before although I would be wary of using a charger especially if a modern 'intelligent' type.

If this were my problem I would proceed as follows:

Once wiring replaced/repaired, leave out all the bulbs including front lamps and indicators, and remove the SW connection from the coil. Connect the battery via an inline fuse holder (crock clips either end) with a very low - 1amp radio - fuse in it.

Turn on sidelights then wiggle/pull/play with loom from back to front. If that doesn't blow fuse it's likely that loom not shorting to earth. If fuse does blow you have isolated the problem. The use of low rated fuse will prevent damage to your new wiring. Remember that the rating of a fuse is not the current it will 'blow' at but the current it can handle without blowing or getting hot. The blow current is considerably higher.

Next do the same with indicators, then brake lamps (need ignition on hence isolating coil).

That should give you a good idea if the loom is at fault or just a consequence.

Also I would have a very close look at the light units themselves and the light switch itself.

Please let us know how you get on.

My charger is definitely of the 'unintelligent' type!

Having a cut-out rated at 8A, instead of a fuse, makes it very easy to check circuits, including short circuits, with no risk to the loom.

What would be the problem with a modern 'intelligent' type?

One of my chargers is of the unintellegent type and is very usefull for checking circuits as IslipMinor says .

Thanks guys for the help will post next week how things go.

What would be the problem with a modern 'intelligent' type?

They need to see a battery connected before they output. If a battery is completely dead (0volts) then they won't work either.

Katy beat me to it. (I would insert a smiley here if I could find out how to do it!!!!!!!!!!!!!)

Yes - my charger (which I made some 50 years ago) won't work unless it 'sees' enough volts of the correct polarity to pull in a relay. I never thought of it as 'intelligent' ! Just 'safe'.....

I'm not sure what you can get hold of - but if you know any handy electrical DIYers you could borrow various things such as a bench DC power supply (with adjustable current limit) or at the very least make up some 'special' test leads.

I've never had to do this on a car... but for fault finding in test rig harnesses I have in the past used a PJ996 battery (6v)
These have a high internal resistance therefore don't give much current in event of a short circuit.
The little 9v PP3 batteries are less 'safe' as they can give enough current to light up a headlight bulb (= not much internal resistance!)
Doing this at work last year, a colleague loaned us a low current +/- 5/10/12v bench supply - which made life pretty easy, and also looked a bit more profess


Alternatives for DIY current limiting (during fault finding etc..):
If you get a 2 ohm power resistor and connect this in series with vehicle 12v battery, this would also do a similar thing - i.e. anything more than a few amps would mean you drop a most of the voltage across the resistor and therefore protect the circuit.
A brake light bulb (20w) should draw less than 2 amps so with a 2 ohm resistor you'll still have enough supply volts.
With a full short circuit you would limit the max current to about 6 amps.

When I installed my new loom I fitted an accessory type fuse holder with a 2amp fuse in between the feed from the battery. ( in my case between the the brown wire & solenoid solenoid battery terminal) so ANY current surge like a wrong connection would blow the fuse before doing any damage. When all was well and tested I uprated it to 5amp to check larger circuits like headlamps and start solenoid primary coil, then just removed it when I was happy.

Simples!

Thanks again guys for all your tips - hoping to get onto the car this weekend but struggling with a bad cold at the moment

I prescribe a large tot of Malt Whisky, followed by another - until you feel 'better'......

and another and another .etc,then you won't feel anything

I've shtaken the malt whishkey ash preshcribed by BMCEcosh and kennat and now I don't really care about the wiring loom