change oil soon light/computer

The 'change oil soon' light on my 91 PA never worked, didn't light up on ignition as well. Now I notice the computer to which the reset button is attached (under the passengers side dash) was not connected.

I connected it and the light now works. But it keeps lighting up. I tried to reset it, it blinks 4 times as stated in the manual, but then lights up again.

What could be the problem? If I recall correctly from a previous thread, it isn't activated by a sensor but by a calculation.
Also what other functions does this computer control?:confused:

The GM Oil Life Monitor System is not a mileage counter or a separate computer; it is actually part of a computer based software algorithm within the ECM that determines when to change oil based on engine operating conditions. There is no actual oil condition sensor, or additional computer. The ECM continuously monitors engine-operating conditions to determine when to change oil. If the system was not reset (refer to owner's manual) at the time of oil change, the system can be reset as long as it's been less than 500-miles since the last oil change. If this mileage has been exceeded, change the oil at 3000 miles and reset system.

The ECM controls all engine & most transmission functions

Thanks for your reply. I suppose if this box controls all engine functions the car wouldn't be able to drive as properly as it does?
Here is a picture of the lower dashboard panel with the computer on it as I found it.
http://www.imageno.com/thumbs/20090811/w3ujpeaze2dd.jpg (http://www.imageno.com/w3ujpeaze2ddpic.html)
The oil life monitor computer is the metal cased box on the right. It has "general electrics" on it.
The Gemini boxes are aftermarket alarms I think.
Just above the round floor light cup, you can see the connector that should be in the 'oil life computer'.

I am wondering why it can't be resetted and if it controls any other warning lights, because there are a number of other warning lights that do not work (while the bulbs are ok)

Well I tried to reset the computer again, both with the ignition on 'run' and with the engine running. When I press the button the 'change oil soon' light blinks 4 times, then goes off for a second or 2 and then lights up again.
Any ideas?

I suppose whoever installed all the "Gemini" boxes had the same problem, so they disconnected the wiring. The after market alarm system probably has an effect on other lights also, especially if it has a remote start system that would bypass the ignition key reader. No easy solution here!

I've never used or tested the after marked alarm system, it seems a bit complicated...

Do you know whether the box with the oil reset button does have any other functions than calculate the next oil change? If it does just that, I'm not too concerned about it.... and will disconnect it again. I am used to remembering when to change the oil.