MG F/TF Front Fogs - Parts, Wiring Diagram, Installation Guides

Hi yes, my car is an F mk1 withe a mk 2 consol with mk2 switchs, the fog lights and the loom came from the same car and worked at the time of removal.
there was the two lamp plugs that fitted correctly, then a ground to the inner wing, next came the under dash wiring following Roverlikes diagram to the letter. I still have part of the loom as I wanted to keep the plugs to use again. the loom I assume was fitted by a dealer but there are no labels on it to say so but looked very professional make up.
It came with a 20a inline fuse ( still intact ) and the relay with markings, 20 200 100 12v 30a and the diagram showing contacts open.
It didnt have a switch but i had a couple of spares so was good, or so i thought as today i looked for the original one i used but must have binned it as it was a write off but looked at the others, I have 2 yug102590pmp but one shows the on the button a front fog light and the other a rear screen heater and 1 yug102570pmp showing a front fog on the button so im wondering if the body was wrong on the melted one as i would have just looked at the button.
I havent checked to see if the lamps worked still but will check now.
I cant remember if the switch plug was difficult to fit or not as it was last year.

Hi, no it was only melted under the dash at the switch, the relay and connection to the fusebox, looking at the switch plug it is the red/black wire thats melted, at the relay the red/black wire again. plus the black/grey wire, the others are intact apart from melted pvc from the other wires.

Do you want to run with this one Notanumber, it might fog Pipl if we’re both at it & as you’re already teasing out the sort of info I would be trying to solicit, it would make sense.
One point which might be salient is switch type. My car is Mk1 with Mk1 switches which when factory fit fogs we’re installed had a latching switch, at some point in production a momentary switch was fitted, one of which I acquired in error for my system (all after market) & I built a latching circuit to switch the lamps. I changed it to latching later but only because one fell of the back of a wagon.
M

I am questioning the wiring here or the connectors.

I checked switches yug102590pmp and yug102570pmp and basicaly they would do the same thing. So I am not blaming them. As I can see the wires melted on the relay it seems that relay melted its inners and as consequence joined the coil terminals so switch was short circuited as well.

This would draw me to conclusion that when switch was pressed relay connected high power terminals, but for some reason other high power terminal was connected to the ground. So short circuit was created.

What bothers me is that in-line fuse stayed intact. I do wonder to which wire this fuse is connected then?

Post removed as overtaken by Roverlike's more detailed one

Actualy after some more thinking and looking into wires which were fried and which were just burnt, seems to me that relay coil gave up and made short circuit between coil terminals propagating short circuit down to the switch.

Fuse is not burnt since there was no short circuit on the hign power circuit, just burnt high power wires because coil terminals were shorted.

However I would expect that fuse for illumination must be burnt due to this, in the fusebox under steering wheel.

Hi, the inline fuse is on the thick brown wire going into the relay.
I have pulled the relay case off to look inside and as you can see its perfectly intact with no signs of burning which is a shame as it would have made lots of sense, ( a dead short ) but going through the coil, on testing it i get 65.7ohms through pins 85 & 86 which is across the coil then open circuit on pins 87 & 30 & then a dead short when the contacts closed. however, checking the resistance of the coil again, i get the same reading closed or open but as you close the relay i get an audible tone of continuity just for a nano second but doesnt show that on the LCD display.
Also is the switch supposed to be latching or not .

Unfortunately I cannot see any picture.

If the relay is normaly open relay, then you need latching switch. Fuse on thick brown wire should be between direct connection to car battery and relay then.

At that moment you hear continuity on relay coil is the moment when you have short circuit in coil circuit.

Sorry, I forgot to add it.
The thick brown wire with inline fuse was connected to the terminal in the fusebox as in your diagram.
I have another fog switch that is a latching one but alas no part numbers on it but looks the same as the other 590's

Early in my ownership of the car, I had a major melt down of the wiring loom that runs along the front left side inner mudguard, (inner wing to you Pomgolians) to the front lights. I repaired the damaged section of wiring loom, but I never found the exact cause, obviously somewhere in there a short had occurred but as it was burned to a crisp, I couldn’t tell where.
It’s possible that it might just have been a shitty loom.

Hi all, me again. 
ok so now I have managed to sort a replacement loom from a mk1 car with a mk1 consol. As I mentioned before, I have a mk1 car with a mk2 consol (still with me ). 
ok so the loom has everything on it that worked ok on the car. But I need to swap the mk1 switch with a mk2 switch and of course it’s not a direct swap. 
on the mk1 connector to the switch is 5 wires   as per picture, I don’t know if this configuration would be the same for the mk2 switch, if it is can I simply heath robinson the connector to fit. 
cheers. 

Not sure I am able to follow you. Mk1 and mk2 switches have the same connector. If this is not the case with you can you show me what type of switch is your mk2 switch? What type of connector is expected there?
Second it is extremly hard for me to say anything with 5 wires to the switch you have in your hand without knowing what each wire is connected to on the other end.