Yep the bolt holes are different and also the size of hole going into the manifold from the throttle body is a different shape. Also an OBD1 manifold requires n extra hose to be connected.
The light will usually go away if the fault isnt present any more and was an intermittant fault. In my experience you have to drive for a few meters for the ecu to recognise the fault has been cleared.
I think what you are talking about as I have just fitted a MOMO wheel to mine and had the same problem. Basically you should have one wire coming from the boss which you connect to one of the contacts on the button. The other wire should be connected from the other contact on the button to a contact on back of the wheel. Is this what you have already done?
Phone the citizens advice www.adviceguide.org.uk as they have been quite useful for me in the past month or so. I think TBH you should get a full refund as you have told them everything. And at the end of the day they provided you with faulty goods and you are within your right to ask for a refund.