Myserious switch and dial

Dear all

I recently purchased an MG TF and on the dash next to the steering wheel there is a switch and dial and I cant seem to figure out what they do. The garage i bought it from also didn't know, i guessed it was for the engine fan or power steering but it doesn't seem to affect either of these (i checked the fuse for the fan and it seemed fine). space under the dash is limited so I can't really see which wires go to it but there appears to be a relay or something that but i cant hear it activating when i flick the switch or play with the dial.

any ideas on what they could be for?

There was a spell when folk were fitting fan override switches on the cooling fans & I’ve seen diagrams with a variable speed system engineered in.
Many garages decommission DIY add on items, usually because they have no idea what it does & you either end up with mysterious holes in the dash or worse still mysterious switches & knobs.
Just a thought.
M

It’s nothing that is OEM, anybody’s guess as to what the afterthought is/was for, trace the wiring to where it goes is probably the best way to figure out why it’s there

:welcome2:
Do you have plasma dials fitted to the instrument cluster?
From the tiny section I can see in your first photo, it looks like you have. White dials with blue and red figures?
If you do, the switch and rheostat are likely to switch on and adjust the illumination.

Yes I belive thats what they are, i would like to switch them back to the originals, i think they are just stuck on over the originals as from what i can see through the goles around the needle hub. my RPM and MPH are off by about 100-200 rpm (based on OBD2 readings) and based on gps about 8-10 mph which is a little concerning on the speed side, so not sure if that san issue from the dials being misaligned or the cluster itself.

Ill check that tonight when its dark thanks for the suggestion.

That does appear to be what the switch and dial does although interestingly the factory brightness adjustment also works and the switch seems to change between the brightness value of the factory adjustment and the aftermarket adjustment under the switch which is very odd

A word of caution. You need to remove and refit the needles to remove the plasma dials. This is fraught with danger! When I fitted mine I had to buy a second dial cluster to replace a broken spindle on the speedo.
Also the standard speedo is pretty inaccurate especially with 16" wheels fitted. (On the over generous side)
The standard dials are pretty naff in my opinion...

Thanks for the warning, although that doesn't seem to be an issue now as the speedo has just decided it doesn't want to work today, The OBD2 reader shows the speed sensor works, but who knows maybe it'll decide to work again tomorrow.

Edit: it appears smacking the binnacle has mad the speedo work again

Don’t smack it too hard, a replacement in good condition would be quite expensive & they do break of their own volition without any input from the owner.
M

I doubt that I hit it any harder than dome of the bumps on the road around here do.

If the speedo is unreliable it might be easiest to get a 2nd hand instrument cluster, there are plenty around for sensible money.

Notanumber wrote:

If the speedo is unreliable it might be easiest to get a 2nd hand instrument cluster, there are plenty around for sensible money.

+1 on this, not worth the effort buggerising about with!