Hi, there should be six wires from the mirror to the round plug, two for each motor and two for the heater element. Once they go through the round plug two wires are paired so that brings it down to five. See the diagram below..the other side is exactly the same. I hope this helps.

I looked through all the wiring diagrams for 86 onwards and cannot find any different wiring, all mirrors appear to be the same.

Six wires coming out of the tube is normal as shown on the diagram. However, if your mirror has five wires you might want to take it apart and see where the various wires go, and if someone has done anything 'non-standard'. Of course, the question is...why are you replacing it - does it actually work?

Was there the option of a heated mirror ?

That's a very good point. This is a standard 8v 944, but I have to admit, I'm not quite sure on the models as of yet as I'm quite new to them.

See if you can manually adjust the mirror and peer inside , you might see a wire attached to an element on the rear of the mirror, that's if it's the original mirror ?

If the wires connect directly onto the mirror glass itself then I would say its a heated mirror, and it would be more than likely activated when you press the button for the rear de mister , I could be wrong but that's generally how it works.im new to Porsches myself so somebody else may be able to confirm this

Yep, that is how it works - if you look at the diagram I supplied you can see the heater element connected to pins 5 and 6 - a brown (ground) and a brown/yellow wire. A white and white/brown pair go to one motor and a black/brown goes to the other motor. A link wire should go to this other motor and connect to the white/brown.

It is difficult to tell the colours of the two sets of wires in the photo, so I can't suggest anything further apart from taking the glass off - easy with a screwdriver in the hole underneath (see clarks garage for explanation - http://www.clarks-garage.com/shop-manual/body-10.htm) there is a rotating locking ring assembly. Unscrew the motor plate and see where the various wires go in both mirrors. It could be that the link wire has been made there rather than at the plug, so that might account for there only being 5 wires. However, a visual inspection will reveal all...

It is possible (as your car is an 86) that your original mirrors are the older style and the replacement is the later. I cannot find any mirror wiring diagram for the older style in the 944 workshop diagrams - they seem to be completely missing - so I cannot confirm the earlier wiring. Are the bases to the mirrors the same shape/profile? I think these changed for the later versions and a hole is provided to access the locking ring - otherwise they do look similar.

Like I suggested, I think the best course of action here is to take them carefully apart and inspect and compare - the situation should become clearer then.