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MG Midget and Sprite Technical - Fuse or not?

I've recently added relays and fuses to the headlamp circuits of my midget. The twin aims were to save the low-quality pattern switches from having to handle the current drawn by my uprated lights and to reduce the risk of fire from shorts in the wiring at the front of the car.

With the safety aim in mind, it concerns me that the switch circuits are still supplied directly from the solenoid, with no fuses. Even the side/tail light fuses are downstream of the switches. So all the behind-dash wiring remains unprotected - a short will still burn the loom, at best.

If I correctly read the wiring diagram, the big spade on the solenoid feeds only the lights, cigar lighter and radio. The maximum total load, now that "lights" only means relay coils, must be low enough for a regular blade fuse.

My question is whether other people who have added relays and fuses to their headlamps have also added a fuse to the switching circuit and, if so, what rating. Or, if not adding a fuse, was that for a good reason or did they just not get around to it?
Pete AC

I'm planning to fit headlamp relays and to fuse each filament separately, so if a fault on one causes a fuse to blow, it doesn't take out all the lights.

A fuse on the switching circuit will have the effect of taking out all of your lights in one go....although a fire behind the dashboard could feasibly do the same, I suppose.
Dave O'Neill 2

I shared a fuse from the light switch to the side lights and panel lights. If that fuse blows I will loose all "side lights" but the loss of the panel lights should give me an indication of the fuse failure.

Dave: won't that mean four relays and running additional wires up to the headlamp?

Remember spade fuses are rated at their running current and are not a direct like for like replacement for Lucas glass fuses as far as ratings are concerned.

Graeme Williams

"won't that mean four relays and running additional wires up to the headlamp?"

Yes, that's what I had in mind. Still at the planning stage at the moment.
Dave O'Neill 2

That would be pretty foolproof as far as safety goes Dave. Unless you take into account upstream of the relays.Whatever you do, it must be better than the "out of the factory" no-fuse standard. Except that when the lights fail due to a complete short, you can always illuminate your path by the flames from the wiring!

The only thing to take into account I guess is that ex-factory you are only going to loose lighting in the event of a major failure (but it would be total). Each fuse, relay and so on introduced increases the potential for further failures, abeit probably not total. Less reliability, higher failure probability.
Graeme Williams

I thought I replied earlier but no sign of it.

I realised that my suggested extra fuse might be unwise as its failure would take out every light on the car. Without it, a blown fuse leaves one with sidelights (and headlamp pilot lights in my case).

Pete AC


--FUSES--
I can't believe what you're doing here--
headlight circuit fuses have been frowned on for years
Bloo5y dangerous
Don't you have circuit breakers over there
There are a few different types available to suit different situations
You can even buy circuit breakers that plug in instead of fuses with various amperage ratings, these are simple to fit-- a lot safer as they just flash the circuit on and off to tell you there's a problem instead of leaving you in the dark at 600 mph
I'm scared for you ,I thought fuses were illegal on headlight circuits--I'm prety sure they are here
Safety Fast isn't it
willy
William Revit

I thought most modern cars had fused headlights?
Dave O'Neill 2

Yes, all modern cars use fuses in all circuits, apart from the starter motor (with some exceptions), as far as I know. The probability of a fuse blowing is quite low and if it does there is a problem requiring immediate attention anyway. I'm constructing my own wiring loom for the Frog restoration and all circuits, apart from the starter, will be fused. Obviously, if the fuse in the sidelight/headlamp switch circuit (I'll use relays for the headlamps themselves) blows then the headlamps go out. I'm prepared to take that chance.
Bill Bretherton

The fuse is only there to protect the wiring so better a lamp out than a fire!
mark heyworth

I am no electrician, but when sorting out a non-functioning window drop glass in a VW Golf ("nothing is as reliable as a VW"!!)I discovered that a lot of the wiring is switch to earth and is configured so that it simply triggers a neg input pulse signal back to the CPU which then operates and times the function. This means that most of the wiring is along very fine wires which are at ground potential so little chance of fusing or overheating, and I think no relays in those switch circuits. The relays and fuses are in the output cabling to the various powered components which is all in much heavier wiring.
Guy W

Exactly Guy
Was the Golf a mk5 --windows are real fun on them

SOME moderns have fuses in the light circuits
They normally have 4 ,one for high beam ,one for low and the same for the other side light

They would be better with circuit breakers in my opinion

Having said that, most modern cars have their controls going through the body module or instrument cluster
Most controls going to a controller / pcm are earth switched or more likely can controlled and the module then operates the relays etc as demanded
The only live power will be from the relays (usually under the bonnet) to the headlights--A short distance and unlikely to get shorted out-----not like bullet connectors falling out and running around looking something to weld themselves to

Bill- Why not use circuit breakers instead of fuses in the headlights- it's a lot safer and easy
I'd much rather have flashing headlights than have the lights go out completely---------????
You can get them in 10-20-30 amp & ratings and they just plug in instead of blade fuses--

willy
William Revit

Willy
I wasn't familiar with auto resetting circuit breakers but will look into them. I don't think they're common here.
Bill
Bill Bretherton

Willie - it's a MK6, though l had the exact same problem to sort out on my son in law's MK5 last year. Tracing the wiring and the fault with a meter, no wiring diagram and my limited knowledge was something of a mystery at first. Trying to work out which wire's did what and they all seemed to be dead had me puzzled for a while until eventually the penny dropped !

Those miniature MCBs sound a neat idea, especially if they are a direct plug in replacement for spade fuses. l think l will replace my 2 up, 2 down headlight fuses, not that l have ever had any bother with them. Yet!
Guy W

All very well but 'if it ain't broke - don't fix it' still rings true to my ears.
David Smith

The original Sprite/Midget wiring is perilous to say the least with unfused circuits. If you have an original loom it's probably worth modifying it before The Prince of Darkness accessories have their wicked way.
Bill Bretherton

That makes no sense at all. It's been fine for more than 40 years as have many many thousands of other similarly designed and wired cars. How many standard ones have spontaneously caught fire? As a percentage I'll wager a large sum that it's less than the modified ones.
David Smith

David, which bit makes no sense...the relays or the fuses?
Dave O'Neill 2

Fuses; I do appreciate that some / many repro column switches are crap quality and don't take kindly to the full headlight current.
David Smith

Bill / Guy
If you can't find them, maybe your Ford dealer might have them
Ford here use them a lot on things like boot releases electric windows and door locks,--Anywhere that a switch can be held on too long and would normally blow a fuse-----------they're a good investment,and come in both the normal blade fuse size and the mini

Happy New Year
willy

William Revit

David, I was referring to old wiring looms which will have degraded insulation. They don't last forever. There's no way I'm going to use a 58 year old wiring loom (although mine has been hacked around which makes it worse). When I was younger I had a much more cavalier attitude to these things, but not now. As you suggest, probably very few have caught fire. It's just that I don't want it to be mine.
Bill
Bill Bretherton

If you're renewing the whole wiring loom then you don't 'need' relays or fuses/circuit-breakers on the headlights but if you 'want' them that's fair enough.

I've never really understood this Prince of Darkness stuff, your wiring loom has lasted 58 years after all, the term should refer to piss-poorly made modern parts.
Nigel Atkins

Well it's been off the road since 1980 so was only used for 22 years. The loom won't be connected to a battery again. Surely, relays make more sense for the headlights as there is then shorter cable length hence less volt drop. Also, an ageing light switch might struggle with sidelight and main beam currents.
Also, I have to say Lucas isn't in the same league as Bosch imv. When did you last use damp start on a modern car distributor?
Bill Bretherton

When did you last see a modern car with a distributor? ;o)
Dave O'Neill 2

Gday all
Having renewed/rewired my 78 1500 here are my observations:
1 the wiring in my loom was generally OK except for the terminations where dissimilar metal corrosion and moisture had caused issues- solution was to reterminate with modern spade fittings (don't use the crimp ones solder and heat shrink is the only way to go)
2 some earth wires to the headlights had "black wire syndrome" and had to be replaced, so I doubled the earth by having an earth to the body for each side.
3 I replaced the old fuse block (4 fuses) with one scavenged from an old Datsun (12 fuses) and added extra wires for good measure i.e new ignition supply
4 relays for Hi and Low beam, engine fan and the ignition connected to a high energy system.
5 all relays are protected by resettable circuit breakers (see pic) - headlights run from one 40 amp and the ignition and engine fan from one 25 amp - all supplied from one new heavy duty wire directly from the alternator connection to the battery
6 all relay outputs are completely new wiring - DON'T USE THE EXISTING WIRES FOR THIS
7 if fuses are needed you can use fused relays

Ok this is a lot of work and quite daunting for some but the results are impressive especially the headlights and ignition - she starts first time every time and I can see in the dark
HTH Cheers all, happy new year
Rod






R W Bowers



The Prince of Darkness

The Prince was driving along in his MG and being late in the day he thought it was time to turn on his lights
Like most cars of that age his car was fitted with the special L$#as light suckers
With his light suckers turned on, the special lenses sucked the light in and fed it into the now, bright globes which in turn fed it down the brightly coloured wires to the battery 'smoke holder' Some cars had two so they could hold more smoke
After driving along for a while the battery got full and started to smoke out it's vents. The smoke then travelled back up through the wires turning them black and they started leaking smoke into the car
The headlights started to fill with smoke and wouldn't let any light through-leaving the Prince in the dark

The Prince's Theory now is-----
The bright coloured wires carry the current and sparks
The black wires are earth wires
If you rub a bright coloured wire on the body to make a hole in it the sparks will escape and the wire will go black and become an earth wire

lol
willy

William Revit

Bill,
I can't ever remember using damp start on any of the classics that I've had as 'dailies' for the last 25+ years.

As for the quality of German cars and car parts from what little I know whilst generally the quality is high that's not always the case, "German engineering" is over hyped, usually by the owners of German cars. Friends of mine have had strings of BMWs and Mercs and they had problems with them especially the Mercs of certain manufacturing years.

Whilst the owners of British classic cars accept low standards of replacement parts and components and insist on the cheapest available the standards will be low but perhaps we can help drag the standards up a bit
Nigel Atkins

Nigel
I have memories from the early seventies of using damp start on my minivan distributor, trying not to be late for a date, but that was a mini problem I guess with the dist. at the front so it caught the moisture (they were covered later I think). But also I remember abandoning the then Sprite one night (mk3) due to damp electrics. Went back for it the day after and got it going. Great days. BMW, Merc? Never had either, I've been a Volvo man since 1986.

And Dave is correct, of course, about the lack of distributors now. Happy New Year.
Bill
Bill Bretherton

Rod B. made good points: all but one of my wiring woes (also '78 1500) have been down corroded original bullet connectors and blackened earths.
Unlike Rod I have used crimps, but I get premium quality crimps and use a proper ratchet type crimping tool. Every time I find one of the cheap squeezie pliers type I dump it, they're worthless.
For corrosion protection I use Scotchkote. It can be messy if you're impatient but it works fantastically well.
For replacement earth wires I've taken to using marine grade wire, as I was given it for free. It is stranded like auto wire but the strands are individually tinned all the way. Plus there is some sort of glue between the conductors and the insulation. Makes it a bugger to strip but it stops capillary action drawing moisture up the inside. I expect it to be good long after I am dust.
Greybeard

"but that was a mini problem I guess with the dist. at the front"

Yes, indeed later Minis and ADO16s had a cardboard(?) cover over the front of the engine.

You could also get a rubber boot to fit over the coil - my MGB has one - and possibly the dissy, too.
Dave O'Neill 2

As for the quality of German parts it can depend on if they actually are. I believe Bosch had a problem a while back with a sofisticated copy. The parts and even the packaging looked correct but the quality was poor. Also like most large companies now they have factories in places where it is cheaper to produce and quality may suffer as a result.

Trev
T Mason

When I rewired my headlights (see an earlier thread on "power source for headlights") I fitted relays for main and dipped each with its own power supply and a 15 amp fuse. That way it should be possible to have main or dipped if one of the fuses blows and not lose both beams if both relays were powered from the same source and only one fuse (as would be the case with the MGOC relay kit). I think some one on this BB suggested this. All other wiring is standard.
Chris Hasluck

Circuit breakers to replace the standard 'blade' type fuse are available from Vehicle Wiring Products or Demon Tweeks:

http://www.vehicle-wiring-products.eu/product.php/1247/blade-circuit-breaker

http://www.demon-tweeks.co.uk/Product.do?method=view&n=1277&g=253317&p=253360&d=124&c=4&l=2&utm_source=Google&utm_medium=Base&utm_campaign=Circuit%20Breakers%20&%20Fuses&gclid=Cj0KEQiA7qLDBRD9xJ7PscDCu5IBEiQAqo3BxE2AYJN8m-ZmXpFP7jK1cF2PadJSH2UywokeLmMuz1YaArjQ8P8HAQ

Didn't know they were available when I added fuses to all the lighting circuits last year (2016). They are not cheap at £5.25 + VAT, but might be worth considering?

Richard
Richard Wale

Chris H describes exactly what I did. My thinking was that if a relay fails it would either be the Hi beam, in which case no drama - still have Lo beams. If Lo beam relay fails it takes seconds to swap the wires over and still have Lo beams working off the "wrong" relay.
My main motivation was to minimise the loads on the stalk switchset.
Now I too am seriously thinking about the resetting breakers.
BTW the MGOC kit came with solder type connectors; exactly half the number needed, which was mildly irritating.
Greybeard

Bill,
yes I also had problems when I used company minivans in the mid-80s.

Dave,
when I first got my previous Spridget remembering the problems with the minivans I bought boots I think to go over the coil and certainly the dissy cap but I found the dissy cap boot too tight to fit and when I asked someone about this they advised me not to fit the boot as they'd probably hold moisture so self defeating (dissy cap boot at least).
Nigel Atkins

This thread was discussed between 29/12/2016 and 02/01/2017

MG Midget and Sprite Technical index

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