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MG Midget and Sprite Technical - Melting Switches

I put a replacement headlight dimmer stalk in my '72 midget about 3-4 years ago.

The other evening I had no lights at all. Upon investigation I found that the stalk had melted at the blue/white (high beam) wire and shorted out the switch.

This is probably the same issue that had me replace the headligt toggle switch a year or so ago.

I'm assuming it's a bad groung somewhere, or.... could it be that I have an uprated GM alternator?

Any sugestions

Phil 'livin in the dark'


Phil Burke

Phil
Have you altered or increased your headlight wattage? The maim cause of switch failure is over current,causing heat at the contacts.and as you have also had other switch failures. I dont think an earth fault would cook up the switches.
Noel Copping

A short at any point in the car's life will soften the plastic, causing the riveted joint to be loose. This is a high resistance connection, aka a heater, so it gradually melts things, getting more loose and more resistant as time passes. Quite possibly the same fault long past was responsible for both failures. Alternatively, plain old contact wear and corrosion will do the same, especially if the car has sat unused for periods.
A good argument for relays, to remove those heavy loads from flimsy switches!

FRM
FR Millmore

GEZ!

Thanks FRM. That painless aftermarket wiring kit is looking better by the day, perhaps Ill wait on the suspension and brake upgrades in favor of safer wiring

Prop...painless is not just a state of mind but a real company
Prop

Step away from the car Prop. Do not touch any wires. Do not use a "painless wiring kit" It ain't, and you have enough things that don't work now.

FRM
FR Millmore

Prop, listen to FRM, stay away from the wiring! ;-) Adding relays isn't difficult and is much easier than trying to make an American HotRod wiring kit work with your Spridget. Unless you have something that is extremely modified like my car then a standard harness with a couple of relays for the high and low beams should be all you need for years of trouble free driving.
Phil, I suspect you installed halogen type sealed beam bulbs in your car at some time, they draw a bit more current than the original Lucas bulbs and that will eventually cause old tarnished contacts in the dip switch and light switch to heat up and cause such problems. Replace the switch again and add two relays and you'll be fine.
Bill Young

Adding relays is fine but they only mask the problems. Remember many of these vehicles were made 30 to 40 years ago and some like mine still have the original wiring and switches without problems. My MGA also has all its original switches with not a relay a sight and it is 50 years young.!!

Both my older cars run halagon bulbs with no problems, why? because a 65 Watt bulb draws the SAME current as any other 65 watt bulb. It is not true that these bulbs draw any more power than any other bulb. In reality they are brighter but that is because they are more efficient not more power consumming.

Heat is produced by either a short circuit in the system or a high resistance joint at the switch. Maybe your new switch was extra poor quality it is hard to decide but relays will mask the problem whatever it is, if you can not be certain on the real cause.
Robert (Bob) Midget Turbo

Phil

I have a similar problem with my '78...melted inside the column switch, but low beams do work, high beams don't :(

I've ordered a replacement switch & will relay both high & low beam circuits...I think that's the only way to keep the headlight system reliable with modern bulbs & yes I do have aftermarket halogen sealed beams installed.

Good luck
Dave
Dave Rhine

Robert, don't know what lamps are available over in GB but here in the states there can be enough of a difference in wattage to cause problems with old switches. The standard lamps used on the Spridgets drew around 40 to 50 watts, newer halogen type sealed beams draw 55 watts according to the Sylvania website and that 5 extra watts at 12 volts is another .5 amp of current draw per bulb or 1 amp across the switch. That for a switch designed to handle about 10 amps originally can cause slow heating to occur. That's the reason I and many others recommend relays for the headlights as well as to protect the relatively weak contacts in the newer brake switches as well.
Bill Young

I got through 3 of those column stalk switches since 1999. The first was the original so it had lasted well. But the replacements didn't survive for very long. The reason ? - I am using 100/55w bulbs. Fine on dipped beam but when driving on mains they are drawing a lot of current, and more than the switches or little contacts in the stalk switch is designed for. I have now added relays and the column switch stays nice and cool.

Guy
Guy Weller

Strange, just looked at the manual for size of headlight bulbs and it makes interesting reading
Frogeye main beam is 50 watts
the rest of the Dynamo Spridgets are 60 watts
alternator spridgets are only 50 watts except thise in the USA which remained at 60 watts.

How strange is that?

In the UK the maximum allowed is 65 watts which is the size I use. I will ensure I keep my original switch I think! LOL.
Robert (Bob) Midget Turbo

I like relays & new wires in critical circuits.

I just don't trust my car's 32 year old wiring.

I've already relayed the ignition & carb electric choke circuits.

Each to his own, I guess!


Dave Rhine

LOL Dave yep I am a concours buff and like 1950s technology!!(tongue fimly in cheek) :)
Robert (Bob) Midget Turbo

Bob,
I was lead to understand that UK regulations require that you need to be able to operate headlights at 65W or less. And that one interpretation of this is that main beams can be more, so long as they can be operated as dipped lights of 65W or less. My car has had the 100/55W bulbs fitted for a number of years and has had them checked and passed for the MOT on each test without question.

Truth is that in the UK, unless travelling on rural roads in the more remote areas, or very late in the night, there are few opportunities to drive on main beam anyway.
Guy Weller

Bob

Yep, 1950's technology all through my little beast!

I worked as an import car mechanic back in the early 70's...got fairly familiar with the early Sprites & Midgets.

I purchased my '78 last June after being away from these cars for almost 40 years & was surprised (& remembered) how little had changed from the start of the production run in the late 50's to the end of the run as in my '78!

Oh & BTW we didn't have these front hub bearing problems back in the day, just replace them & we were done!

But that's OK, I love my little problem child & will keep on working with it :)
Dave Rhine

Hmmmm
Guy I think you are illegal cos I believe that main beam is limited to 65 and dip I think is 45 or 55 not sure of that one. Might be wrong though?

Obviously the only sure way to tell the size of bulb is to remove it so when you go for MOT there is no way on earth you will get a fail.

I suppose what could happen is if you were involved in an accident perhaps the other party could claim being blinded and he police could check your lamps, then I wonder what would happen.

Might try that myself if ever I have an accident. :)
Robert (Bob) Midget Turbo

Well, as I said, the lights have been checked for the MOT several times now (on a beam tester) and passed as they are. The dipped is 55w, not 65w. I was told that so long as they could be dipped within the limits, the main beam wattage was OK at 100. Perhaps they are illegal, but that isn't what I was told.

But oddly, I have it in my mind that 120w ones are. Possibly because 120w bulbs come with a higher rating dipped element as well. They are sold with a disclaimer on the packaging "for off road use only"
Guy Weller

I think the standard UK sealed beams were 60/45W and H4 bulbs were 60/55W.

I remember seeing 100/55w and 130/80w bulbs being advertised, but they always stated that were not legal for road use.

I'm not sure what the legal maximum is, but I'm sure someone around here does.

And Guy, as Bob says, how would the MoT tester know what wattage your bulbs are?
Dave O'Neill 2

Dave, Bob,
Don't get me wrong. I am not insisting that I am legal. Only saying that I was told that this was OK. And that it has passed its MOTs like that - which as you point out doesn't prove anything!

The point was to confirm that putting 100w (X2) through the column switch does cause them to overheat!
Guy Weller

My switch is on its way thanks to the fast sevice of LBC Co.
Can you illuminate me as to relays. What I need to buy and where to instlall them for the headlight (high and low beam) circuit?
Phil' 'no puns here'
Phil Burke

I put the relays on the RH side of the rad support, so you can use the existing H & L beam wires as triggers, and run the headlamp wires straight off the relays. Correct relays have double 87 (switched output) terminals, so each light gets its own wire. I run two fused 14ga power leads straight off the starter solenoid, one to each relay.

This all adds up to two extra wires with fuses, and no cutting of the harness. Relays and sockets from Daniel Stern Lighting. He also has good in line fuse holders. You should have some Lucas bullet connectors to make jumpers from the harness wires to the relay sockets, and from the sockets to the light wires. Nice but not necessary to have some correct coloured wires, which you can get from British Wiring along with the connectors. Get a bunch of single and double connector sleeves as well, since these are the most common fail point of Lucas systems. They go away with age (crack) and the lifetime appears to be about 30 years max.

I also replace the headlamp pigtails with 14 ga and HD plug sockets from Stern. Be liberal with grounds, 14 ga also.

If you do all this you will not only save your switches but have vastly improved lights.

Attached pic is of an MGB done the same way. In this case I added a fuseblock next to the OE one instead of using inline fuses.
DCP_0587 front panel & grounds

Headlamp relays, high & low beam

Note grounds at fender mounting bolt. Long bolt with shakeproof washer and double nuts, clean junctions to bare metal, Oxgard
14Gauge from RH headlamp, direct ground from park/turn lamp socket, ground connection to harness black – also grounds fans & horns.
Duplicated on LH side, direct connection 14 ga from LH headlamp, etc.

FRM


FR Millmore

Phil

Relay the headlights!

That was my project for last weekend & the results were great.

Replaced the dimmer switch, then relayed the lights...man what a difference! My 55/65 watt halogen bulbs now look like halogen, instead of 2 weak flashlight bulbs.

It takes a little forethought ( which I didn't do & had one light going high & the other going low), but well worth the trouble!

I bought a harness with relays from Vic/Brit, but the relay wiring was wrong & I had to spend more time sorting it out than actually doing the wiring.

I wouldn't recommend using their harness...it sucks to have to troubleshoot new parts!

If I did it again I'd just purchase what I needed & make up my own harness.

But, it's done & I really like the results.

Dave


Dave Rhine

This thread was discussed between 18/01/2010 and 25/01/2010

MG Midget and Sprite Technical index

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