Blower resistor complete confusion - Pictures

[Stevieabz]

1986 325i Sport M-Tech 1

So, My heater/cooler blower only works on 4 (full). So I decided to order this - http://www.ebay.co.uk/itm/232022875972 - It says it should fit my car and I double checked.

After I removed my old one I found that my heater resistor plug only has three plugs for what is now four plugs on the new one.

I'm very confused as it looks like my old resistor has been modified, or something weird. What is that screw and what is the wire that comes and connects to it?
And why do I only have three plugs and not four? I've done some research and found that there are two types of heaters maybe? One with four and one with three.
Maybe this isn't the original unit? So many maybes..

Everything is pictured below, sorry for the size, please zoom out.









Any advice welcome, thanks.

[Stevieabz]

Okay! So, I think I have a three speed blower with a four speed blower switch, a four speed blower interior panel -

http://www.ebay.co.uk/itm/Bmw-3-5-SERIE ... Swo0JWMNwF

and some weird modification to make it work. The third coil that has been added to this, what a appears to an extremely overpriced resistor is to thin and get super hot to the point where it has melted my blower cover.

I think I need to buy a 3 speed switch and a three speed early interior panel. Sort the blower itself out as I think it may be broken. One of the pins gives no readings at all and I think that's what this wire and new coil are bypassing.

Just an update for anyone interested.