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MG MG Y Type - Lighting wire melted.

Arrows show the red supply wire from the Main Lighting Switch, feeding to the Junction Box and on to the front side lights and rear tail light(s). On preparing for a drive yesterday, coincidentally with new halogen 35/35 globes fitted, ignition on, lights checked - and smoke emitted from under the dash and the bonnet. Aborted quickly, battery disconnected, and (illogically) thinking to limit damage, as the insulation was still bubbling, I cut the wire - hence the break and the two arrows. No other lighting wires appear to be affected - just the single red feed wire.
The previous incandescent bulbs had operated apparently without any problems. The loom is new and correct from NTG.
No fuses have blown - the Control Box is new, electronic with appropriate fuse protection.
I'd be surprised if the halogen headlamp globes are responsible for the melted insulation - I wonder whether a short to power in the switch (original) could feed way too much current through this particular wire?
Does anyone have similar experience to share, OR, anyone have an idea what might be the cause of my trouble?
I'm in a strange city far from home, so will hope to seek out auto electrical expertise tomorrow - but would be grateful for any advice .
Thanks all.
John.


J P Hall

John, it's difficult to be certain without standing over the car with a meter in my hand but a few things come to mind. Firstly, the red wire which has burnt is doing what it was designed to: supplying current to the circuits attached to it. Unfortunately it has been supplying more than this wire is capable of. Therefore the problem lies with the circuits it supplies rather than the supply per se. By this reasoning it is unlikely to be the generator or control box which supply the current, or the switch. The fault will likely lie with the devices supplied at the end of this wire, probably in the light fittings, rather than the wiring (especially as it was previously OK). Usually problems like thus are down to the last change which has been made; in this case you have to look carefully at the new halogen bulbs. There are few coincidences!
Good luck
Ian
ian thomson

John
it won't be the headlights, they're the blue wires-
The other red wires going to dash lights etc look ok
It's impossible for the switch to put out too much power, it's not the switch causing it----there's a short to earth somewhere
Where that red wire goes out to the junction box,is it sizzled right out to the junction box--- are any of the wires coming out of the junction box sizzled---the usual culprit is in one of the globe fittings where the spring might have broken and shorted out in there or the spring loaded part of the light socket is shorting out on the globe holder housing---If you haven't got a sizzled wire to follow the first step would be to pull the four park/taillights globes out and check the bases/springs etc or pull the wires from the junction box and test each for a short to earth

willy
William Revit

Thanks for comments.
Ian: the concensus among friends here accords with your advice, that the culprit is likely to be either within a length of wiring from junction box to side or tail lights, ( most likely a short from abrasion or whatever), or at the end of a wire where there's a fault with a bulb holder, wiring terminal or similar. Multimeter testing will continue tomorrow - so far the panel switch tests ok and the front right sidelamp. Continuity does not look good in the front left sidelamp suupply - more sleuthing in the morning.
Willy : the sizzling is most pronounced at the end of the run, nearest the junction box grub screw, but extending back towards the loom cloth - but little or no sizzling inside the braided cloth. Then some sizzling behind the dash where again the wire sees the light of day - presumably more oxygen?
No sizzling outside the junction box - just a bit of heat damage where wires are so close together.
I'll be looking at globe fittings as part of the sleuthing tomorrow.
John.
J P Hall

Well, I was nearly right.
Multimeter confirmed good continuity both sides at the front, including the headlamp earths which I extend to a chassis connection.
But when I went to the rear end - bingo: I've obviously shut and locked the spare wheel cover during an event at the weekend, not realising I'd trapped under the edge of the cover, the supply wire to the nearside lights. Result: major short to ground, sizzled wires at left-hand rear, and across to the driver's side, thus affecting all rear lights.
We're nigh on 3,000 k away from home (Adelaide, touring South Australia), so for now I've isolated the affected wiring so that the car can be run, albeit without lights. Back onto the car trailer for the rest of our travels.
Thank you Ian and Willy - both generous with your advice as always.
John.
J P Hall

John, since you are in SA, l expect you attended the Nat Meet in Adelaide. How many Y types were present and who's Y won prizes.

Safe travels, wven if no driving your Y.
Stuart
Stuart Duncan

Hey Stuart - yes, diverted after a trip to Victoria (grandkids etc) to check out the Nationals. Was dragooned into joining in the Y/YT concours with YMG 49, and somehow fluked 3rd Gong. The winning Y was from S.A.(Anthony Pearson), and second was Delia Rayment (Qld). Had a terrific time chatting to some very wise heads from all states, plus a couple of nice drives before I managed to sizzle those wires! I hope the South Australia club will post photos somewhere. I think there were about 8 Ys actually entered in the concours, plus a few others parked around the place. The range of cars and different restoration efforts was awesome.
John.


J P Hall

Hi John, sorry to hear of your short circuit.

I've had similar problems with the wiring inside the spare wheel cover. My solution was to "spiral" some carpenter's string around the wires, tied off to mounting points on the cover and the car body. This gathers & protects the wires from being shut in the cover gap, as well as preventing the wires from being pulled or stretched when the cover is removed.

BTW, there were 5 Y's in the Adelaide concours (we were 5th) and 2 in the speed events.

Happy travels,
Rob
R Ades

Thanks for the feedback Rob - sorry I had the concours numbers wrong. We had never even been to a concours d'elegance, let alone enter a car! It's another world to me - I love the challenges of a restoration, and Jo and I both love driving the cars. Each to their own, definitely.
We will certainly go to future Nationals, but not to enter anything - we just loved the get-togethers, dinner on Saturday (think Tinkerbelle and Peter Pan), and the social drives. Brilliant. I would have loved to have watched the T Types etc on the track.
Now we're enjoying several weeks meandering around SA and Vic before heading home.
Yours,
John.
J P Hall

This thread was discussed between 10/04/2023 and 15/04/2023

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