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MG Midget and Sprite Technical - Wiring loom replacement/upgrade

Hi All, Not visited here for too long.
I've been putting off replacing the loom in my Frogeye for too long but I need to do it this year, the existing one is original and in a poor state, my Frog is modified so a like-for-like standard loom will see me adding bits to it and likely making it look a mess again. So, I have a few questions I hope you can help with. I see Autosparks list a few looms with some additions such as an electric fan and heavier duty Alternator wiring which sounds good to keep it all neat and tidy, I’m sure a conversation with them will be inevitable unless another source is recommended?

Years ago I setup a single relay to avoid all the current going through the ignition switch, I then added separate relays for the headlights on Dip and full beam, this looks a bit rubbish under the bonnet and I was wondering if I should try and add a more modern relay/fuse box to house this lot and hide it under the dash, anyone done this/got any recommendations? I’ve looked at some modular fuse/relay boxes online that look neat but I’d be interested if anyone has done this already or am I wasting my time?

Mark M

Hi Mark
I made my own loom for my Frogeye towards the end of the renovation. I realise this may not be something you'd want to attempt so Autosparks will supply a loom to your requirements AIUI. I didn't use them as it was during the pandemic when they were closed so I used AES (Auto Electrical Supplies) for parts.

I fitted 4 relays in a modular relay box with perspex lid (headlights main, headlights dip, brake lights and horn). I placed it where the original Lucas regulator would be, as shown in picture (2 relays and lid removed). Not everyone would approve of course but I also have an alternator. I have a 4 way covered fusebox as shown (cover removed). I am holding the bonnet wiring multi-way connector which I used for ease of bonnet removal. I still used bullet connectors for interconnections - under dash shown in 2nd picture. Hope that helps!
Bill B

Thanks Bill, did you mean to include images?
Mark M

Ah, well I had included images but then edited the text and the bbs does strange things when you refresh an update. Here goes again:





Bill B

Thanks Bill, that little relay box is almost identical to the ones I have been looking at. I'd like to hide it away under the dash if I can, my engine bay looks like a dogs breakfast at the moment.
What did you do with the Control box?
I converted to an alternator over 30 years ago and I'm sure I had to make some changes to the control box but I don't remember what now, unless I'm thinking of when I converted to -ve earth?
Mark M

If you convert to alternator you dont need a control box. But the lid of it makes a good camouflage housing for your extra fuses.

Like Bill, I made my own loom for my frogeye. i think we did them at the same time, exchanging ideas. The bit that is hard to replicate as a DIY. is the hounds tooth sleeving. I made separate plug connected sub looms for the dashboard and the(removable) frog Bonnet. That way most of the awkeard behind dash can be done before fitting it in the car.
GuyW

Mark
I didn't fit the regulator/ control box as you don't need it with an alternator. If you're having a new loom made you could choose to leave out the control box - you'll never revert to a dynamo I'll bet, they don't compare imv.
Bill B

If the relays are solely for your lighting, have you considered led replacements?
Brighter (and make you more visible) than halogens (headlights) but draw considerably less current and help preserve your switches.
Jeremy MkIII

Jeremy
I had wondered about suggesting LED headlights (I don't have them) in which case the ignition/ light switch may be OK without relays. However, even if the two headlights consume, say, 2A total there's still the possibility of volt drop across an older light switch so relays eliminate that. I also have relays for brake lights (42W so 3.5A) and the horn (3 or 4 amps). I realise both of those are only on for seconds, typically, but the horn "pencil" connector is quite flimsy and the brake light switch (replacement in my case) may well be the same so I'm minimising current through them.

It's surprising how much volt drop there can be. I have a voltmeter in dash (battery condition so called) and had originally wired it off the ignition switched wiper feed (so quite a length of wire feeding it via a fuse). With wipers on the indicated charge voltage dropped too much and the solution was to feed the voltmeter directly from the ignition switch (my ignition feed is fused).

So my wiring does deviate a fair bit from the original.
Bill B

OK, so my next question possibly exposes my lack of understanding of car electrics. I believe an alternator will happily push out 14v to the battery, I thought the vehicle electrics all ran through a regulator to keep the voltage at 12v and not the variable voltage the alternator kicks out? Have I got that wrong? I was assuming the control box was regulating the 12v output to the ignition switch, am I wrong?

I like the idea of sub-looms, I have one for my bonnet already as it’s a flip front and removable, one for the dash would be neat too.
I hadn’t really thought about LED lights, I do have these in my ’72 VW Type 2 but I have read that they can still blind on-comers due to the different light output. I did discover that I had mounted one of the reflectors upside down and fixed that but I need to go out in the dark and check the beam pattern against a nice flat surface, the light output is incredible compared to the old halogen bulbs and has a made a huge difference to night driving.
Mark M

I used LEDs for indicator and brakes, but understood they are not MOT compliant for headlights unless fitted in a complete sealed headlight unit designed for LED lights. And I don't know if such a thing exists for soridgets?
GuyW

My understanding is older vehicles are exempt from this, but obviously that doesn't mean we should go around blinding other drivers hence why I need to check the pattern on my VW, I have read of a couple of people reverting back to halogens after being flashed too much for blinding others.

https://autosceneuk.co.uk/industry-issues/the-law-around-classic-cars-and-led-lighting/
Mark M

Bill, your knowledge of electrics completely dwarfs mine. I'm limited to following instructions rather than having an understanding of the concepts and principles🤔 so don't know what the voltage drop may be.

All the bulbs on mine are now LEDs and the loom is (comparatively)new at 18 years old, so haven't installed relays for brake or indicator lights.
The usual suspect supplied hydraulic replacement brake light switches kept failing so a replacement Mini mechanical one has been fault free - so far. Your solution of a relay would have been the way forward had I thought of it.

Mark, the headlights were from Classic Car leds

https://www.classiccarleds.co.uk/products/latest-led-headlights-h4-philips-z-es-hi-lo-beam-conversion-9-32v

They replicate traditional halogen bulb patterns and I didn't need to adjust them after fitting - using the garage door/wall test.

Guy, according to the Classic Car LEDs site, it is MOT acceptable to use LED headlight bulbs for our cars -

"The MOT rules have been clarified from 06.02.23 to allow the use of LED conversions that pass the beam pattern tests for headlights for Class 3, 4, 5 and 7 vehicles (car, private bus and light commercial vehicle) first used before 1 April 1986 and all class 1 and 2 motorcycles of any age."

Bill, is there any easy way to wire the headlights so they come on when the ignition is switched on? In effect they become DRLs. Thanks.

Jeremy MkIII

Mark M

Dynamos and alternators both produce in excess of 12v - dynamos generally 13v+ and alternators around 14v, as you say.

Although dynamos use a separate voltage regulator, alternators have their regulators built-in.
Dave O'Neill 2

Mark
As Dave says dynamos and alternators are regulated at 13/14v or they wouldn't be able to charge the nominally 12v battery. Both dynamos and alternators would generate more than 13 or 14v if they weren't regulated. Because an alternator has inbuilt electronic rectifiers (diodes) it made sense to incorporate electronic regulation too (using a semiconductor switching device). So your car doesn't need the old external regulator for the alternator - it is superfluous and a potential point of failure. It uses two electromagnetic switches to provide regulated battery charging which can give trouble eventually as the contact points wear.
Bill B

Jeremy
You could use a relay, directly switched on via ignition, to switch the headlights on. Relay coil wired between ignition on (white wire normally) and ground, relay contacts between a battery feed (fused) and headlights.
Bill B

Thanks for the helpful comments.
Jeremy, Those are the exact ones I have in my VW, the light output from them in comparison to the halogens is quite literally night and day.
I'm sure I watched a Youtube video with a detailed analysis of why an LED light output can never be the same as Halogen due to the light frequency (or something along those lines) but my brain couldn't recall any of it and to be honest all I was interested in is can I run LED's on my classics legally.
I have no expertise in this area at all.

Dave/Bill, So I think that answers my question, the cars electrics can be fed directly from the battery and will receive whatever the voltage is, somewhere typically around 13/14 volts?
I just assumed that there would would be separate regulation to 12v only to avoid damaging anything but maybe this is only applicable to more modern stuff.
In fact I thought my VW Type 2 had this type of arrangement because when I first bought it someone had setup a 2nd leisure battery and a split charger which didn't charge. The reason was because the split charger only diverts power from the main battery when it senses over 13v which it never did because it was connected to a regulated 12v output.

Mark M

Cheers Bill, thanks for making that sound relatively straightforward - will give it a try.🤞
Jeremy MkIII

As an aside, I purchased a Chinese DRL controller for my Rover 75. It connects directly to a permanent 12v live supply, with an in-line fuse, but only gives an output when the battery voltage is above 13v - i.e. when the engine is running.

It also means that the DRLs function as 'coming home' lights, as when the ignition is turned off, there is a delay in the DRLs turning off as the battery voltage slowly drops to below 13v.
Dave O'Neill 2

I use relays on both cars for brakes to solve the problem of repeated pressure switch failure. And relays on the headlights to reduce voltage drop on the long cable routes for both, and specifically on the 1275 car to protect the vulnerable lightweight contacts of the steering wheel stalk type switch. The headlights are wired with 4 relays so whether on main or dipped beam if one fails you don't drive into an instant black hole. Unless it's a pothole.
GuyW

Jeremy
A conventional 4 pin relay is numbered as follows:

85: relay coil ground or -ve (on negative earth car)
86: relay coil + (to ignition switch output in your case which you can find under bonnet going to a fuse (white wire probably).
30: connect to suitable battery supply via a fuse
87: connect to headlights high or low beam as required.

In the case of a positive earth car, swop 85 and 86 (in case relay has a diode).
Bill B

There, now you know why Bill and I 'shared' information when each building our own frogeye wiring looms. Sharing, as I recall, was very much one way! He just knows this sort of stuff!
GuyW

Cheers Bill, that's very comprehensive and easy to follow, with step by step instructions.
I just happen to have a couple of spare relays, bought donkeys ago so will check if they're suitable.
Whether your guidance is idiot proof - well we'll soon see...

Jeremy MkIII

Bit of thread drift.

Bought a cheap (£9.90 incl delivery) 4' LED batten for the shed from ebay. Advertised as daylight - 6500k. Weighs about 2 feathers.

Installed and switched on. Hmmm, looks more like warm white. Switched it off then on again, daylight white; off/on again cool white.

So switch on and off twice and I get daylight white. Is this now industry practice standard to have all 3 settings in one?
Jeremy MkIII

This thread was discussed between 15/04/2025 and 16/04/2025

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