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MG Midget and Sprite Technical - Help! What have I done?

As my plans to take the Midget to France next month progress well (engine and suspension now fully sorted), I decided to buy a pair of yellow H4 bulbs (from Ebay) to replace my current H4 halogens that I fitted last year.

I fitted the first bulb and tried the headlights - a little disappointed that my headlight didn't really represent French cars at night from my 70/80's childhood but it was nonetheless a LITTLE bit yellow.

However, when I fiited the second bulb and switched the headlights on - NOTHING! Neither headlight would illuminate on dipped nor mainbeam.

I assumed I had blown a fuse but checked them out and all 4 fuses were still intact. Then I realised that when I switched on the dipped lights, the blue mainbeam light indicated on the dashboard... So I decided that perhaps the headlight switch was damaged and took it out of the dash. It appeared ok so I shorted across the brown (permanent +ve) and the blue (headlight feed) connectors with a short length of wire. Exactly the same result i.e no light on dipped nor mainbeam and the blue indicator light shows on the dash.

Throughout these tests, the sidelights have worked as normal.

PLEASE - give me some pointers?

Thanks in advance

Glynn (not Glenn) Williams

My electrical skills are limited but my first thought would be put your old bulbs back in and if they work it's a problem with the new bulbs
Maybe the terminals are different
Try lighting the new bulb with a house hold battery and some wire touching what should be the correct + & - and see if it lights
Hope it helps
Dave Pratt

Glynn. Dave is correct that the first step is to install your old bulbs and ensure the system is working correctly. If the old bulbs work, the problem lies in the new bulbs. If the old bulbs do not work, something happened when you installed the new bulbs and you will have to trace the wiring back to where you have good power, then forwards until you find the problem. Easy if done in a systematic manner, but highly frustrating if done piecemeal.

Les Bengtson

It sounds like you've lost the earth/ground to the headlights if your main beam warning light illuminates when dip is selected.
Dave O'Neill2

Thanks all for your advice. I did remove the second bulb but it made no difference.

Dave O'N - I will check for the earth connection tomorrow evening and see if that resolves it. If it does, I can't wait to see how I managed to lose it....

Glynn (not Glenn) Williams

check bullet connectors and bulb connectors
Nigel Atkins

Check where the main loom joins the righthand headlamp loom. There is probably a loose or corroded bullet connector there.
Dave O'Neill2

Do you have your headlights on a relay system? If not it is well worth doing.
I had problems with all the switches to the headlights, dash and column, initially through age and wear but latterly due to the column switch being moulded in a less heat resistant plastic resulting in the terminals melting and breaking the circuit and the poor spring function in the contacts when switching from main to dipped.
Relays reduce the current through the switches solving the problem.
Were the yellow bulbs defective, in that they didn't work well, and in effect put a high current through your switches.
I suggest you go back to basics in tracking the fault, use a meter to test continuity, run separate wires for earths, and look at the column switch.

M Myers

Ok everyone, thanks for all your suggestions. I've now got the headlights in full working order:)

After taking loads of stuff apart and testing everywhere with my multimeter, I got more and more confused.

In the end, I simply took every bullet connector apart that I could find associated with the headlights - cleaned up the bullets with abrasive pad and replaced every female connector with new (because I had spares anyway). BINGO! It all works again.

Still don't know why changing the bulbs created this situation but I guess it's all part of the "fun" of owning a classic car....

Meanwhile, I'm now thinking of fitting relays, uprated wiring and 100Watt (yellow) bulbs;)

Glynn Williams

This thread was discussed between 22/05/2014 and 23/05/2014

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