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MG Midget and Sprite Technical - Wiring Mystery

Hi folks, please excuse my dodgy photos that have uploaded on their sides, I hope looking at them doesn’t give anyone a bad neck. I’ll get to them later.

One of the jobs on my ’75 midget 1500 was to replace the burnt wiring loom inside the dashboard. It appears the lighting wires melted, took the horn with them and so a previous owner compensated with extra wiring (household wiring, not automotive) to bypass this, that and everything else with a bucket load of Wago connecters. The probable cause may be the 60/55W H4 headlamps and what with just replacing wires the cause still exists (too much load through the switch) and the risk of an electrical short is probably greater than before.

So, I’ve replaced the dash loom, front loom and all the switches and now I’m fitting 30A fused relays for the dip/main beams. I’ll fit the relays to the NS of the firewall/bulkhead by the hole where the heater cable thing comes through. I’ll run a wire from the switch wire at the FNS wiring junction (pic 2, the 3 blue/white wires are disconnected) back to the relay, then from the other side of the relay to earth. Then run a supply from the starter solenoid to the relay, through the relay fuse and on to the double bullet connector at the FNS (pic 2) where it then feeds both headlamps. I can’t remember if blue/white or blue/red is dip or main, I assume it doesn’t matter just don’t mix them. Then I’ll replicate for the other relay. So one relay feeds the blue/white and the other relay feeds the blue/red.

I think this will give the high beam a fused circuit to both headlamps and the low beam a fused circuit to both headlamps. Switched by the same column stalk and dash switch as before, I’m not planning of changing them just using them to trigger the relays.

I assume a 60W bulb at 12V draws 5A so the max on the high beam circuit will be 10amps, give or take a little. So maybe I’ll drop the fuse to 20A.

I have two questions, I have loads of questions but for simplicity I’ll stick to these.

1. Is my theory ok or will I set my midget on fire?
2. What are the two black blocks in the photos? They are wired into the indicators, the car used to have the rubber bumpers but a previous owner removed them. I think the original indicators now fill the holes in the wings that have been exposed by removing the bumpers (there is a photo of the car in my profile).

I seek your thoughts, advice and guidance and I give thanks in advance.
Nigel B






N Broomfield

I'll have no truck with relays so will leave that to others (apart from that I got a bit lost in your explanation).

As I remember it blue/red is dip beam as I always think it should be the other way round. Best to keep the wiring to the convention otherwise it gets confusing later and your headlight stalk will be ar*e-about-face.

The fuses protect the wiring hence the old glass fuses with 17.5 amps continuous 35 amp blow, the bulbs or filaments will act as a fuse often.

There might be a photo of your car in your profile but you have to check the box to display it in 'Customise' so at a guess the black boxes might be for the front indicators as the white wires come off green wires that are usually indicators. Also the boxes have black wires earthed to the body in the bonnet channel (at risk of being crushed or frayed by the bonnet lipping I'd have thought).

With the modern made bullets and connectors you need to be careful to get all the bullets fully and not under or over reached in the connector, best to remove the black plastic sleeving to check or work the bullets further in or back with a small flat blade screwdriver.






Nigel Atkins

Nigel

Your proposed relay wiring sounds OK to me. Blue/white is high beam, blue/red is low beam. Better to get this right. Fuses are there to protect cables so equal to cable rating e.g. for 20A cable use 20A fuse, continuous rating (or lower) ideally.

I don't know what the black blocks are.
Bill Bretherton

Yep, I reckon your relay plan is good and wiring sounds correct
The black boxes--because they're into the green wires, I'd say your car has led globes in the indicators and those black boxes have resistors in them to get the flashers working properly----'IF' you wanted to dispose of them you could go back to normal globes or get an electronic flasher can that suits the led's

NigelA to NigelB--over and out

lol
willy
William Revit

Personally I'd get rid of those black boxes and their wiring, just more to go wrong in my eyes, or at least tidy the wiring up.

If you have LEDs, though really you want 6 bulbs, four corners and two tell-tale, and those boxes are as Willy suggests if removed you'd also want two LED flasher units, one for indicators and second for hazards.

I'm all for reducing the amount of wires, connectors and components which is why I don't like added relays.

My cheap modern column stalk has yet to burn itself out despite 12 years of H4 conversion with 60/55w bulbs and is it 5, 6, 7 years of the cheap column switch. I think as the lens reflectors have started they will be the first to go. The headlights are bright but that's probably down to the newer wiring and clean, secure and protected bullet connections at the front grille.
Nigel Atkins

Might the black box things be part of, or once part of, an alarm system?
GuyW

I ran a new supply cables from a new fuse box to relays on the front where the headlight connection are and mounted relays there and used the old wires from switches to control relays.


mark heyworth

I can't remember if my headlight main beams are 160W or 130W each (or if 80W or 100W dipped) but they are wired through a relay and work ok [cars coming the other way tend to dip first].

The only change I've made in recent years is to heat shrink sleeve everything including using fatter sleeving for the bullet connectors.

Most recently after stabbing myself in the finger with whatever inappropriate tool I was using at the time, I bought the proper bullet connector squeeze the bullets in the connector tool. I should have bought one decades ok.
Daniel

Even using the bullet connector tool (I've had two different styles of tool) with the modern bullets connectors at least you can still over-centre the bullets in the connector, guess how I know.






Nigel Atkins

Success! 🙂

Now the candles at the front have less chance of setting a fire under the dash (but more chance of setting one inside the engine bay😂).

And it's all removable if I ever find nice LED headlamp units. I know there are various out there (Thomas Performance have quite a range) but they are mostly bug eyed things. I want one that looks similar to the original unit, with a large reflector bowl, but with the halo DLR that doubles as an indicator (a la current Mini).

The eagle eyed among you will notice the water pumper is missing. Tried to fit that today but the new studs were too short to get the nuts to grip enough to tighten 😡.






N Broomfield

I fitted 2 relays for my headlights, one each for main and dipped. I added two power feeds in brown with in-line fuses from the main negative supply. I used the solenoid live as a convenient start point and the wires go along the offside inner wing to the front splash panel where the two relays are mounted in a black box. (ex scrapyard Astra). I wrapped these wires in with the loom so they are hidden.

These 2 wires are only addition to the original loom. I could have got away with one but wanted main and dipped to be independently fused. I cut into the loom by the splash panel to expose the blue/red and blue/ white and used these as the signal wire to the relays, cutting and using them to serve as the feed from the relays forwards to the lights.
GuyW

A useful reference.


Alan Anstead

Is that your Frog Guy, that you added the relays?
anamnesis

Both cars have relays, but the frog has them mounted on the backside of the bulkhead because it is wired with a sub loom for the bonnet, on a multiplug. I know that doesn't really make a difference but a) I prefer the visible wiring to look standard (= basic for a frog) and b) I thought relays might be a bit fragile mounted on a frequently open and closed bonnet.

The later car has 5 relays; lights up, lights down, electric fan, horn and brake lights. The brake light one is next to the 4 way brake pipe connector, the other 4 hide in a black box on the off side splash panel.
GuyW

Alan,
thanks for posting that colour reference chart, I can't remember seeing one with such a clear and simple explanation.
Nigel Atkins

I used to have a relay on an electric fan I fitted, and one for a couple of spots I had at the front. But I ditched the fan when I converted to a crosflow rad(keeps it too cold if I don't keep a 180 stat in all year), and I dumped the spots.

The rocker switches on the later cars don't seem to me to be as robust as the toggles on the earlier cars. If I'd kept the '73 rwa, I may well have put relays on that, for that reason. But on my '66 Sprite, all the toggles are the original and still work perfectly. Even the headlamp flasher on the indicator stork is still ok.
anamnesis

This thread was discussed between 21/01/2022 and 28/01/2022

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