I've recently bought a 1995 306 XTdt and am having a few problems
with it.

In trying to diagnose why the heating blower doesn't work, I'm
finding a few other things wrong with it, and until my haynes manual
arrives, I don't know why certain things are disconnected.

Firstly, there's a relay missing from the box under the bonnet, it's
the one on the left nearest the front (grey connector) - not sure
what that's supposed to do but it's totally missing. There are no
grey ones in the car itself to compare it to, so therefore don't
know what to replace it with.

Secondly, there are two cables plugged into the rubber panel on that
casing (that has no wiring in it - the plugs are red and black I
think, from memory - both wires are white), and two cables below
that are not connected to anything (blue and yellow). Should those
cables that are in the rubber panel be connected to the open
connectors instead?

One of the relays in the box (I think it's the second from the left)
has a wire spliced to the central pin and runs to the headlight.
Don't know why that's been done.

I can't pair the new key I bought to the alarm system as the master
key is switched off, and doesn't match the ignition keys. Doh!

Back to the heating problem, I'm suspecting that the resistor block
has blown, which is why the fan has been wired up direct to a switch
on the ignition. The rear heated windscreen works though - which
apparently is often connected to the blower circuitry.
Do the heating controls illuminate? If so, they're not lighting up.
I fiddled around with the back of it and found that the blower
controls were not connected, so I plugged it back in, but still no
joy - hence suspecting the resistors.

Two wires that hang down under the console near the heater had been
cut off, red and black - I think they're the power leads to the
heater, but connecting them to it still don't give power from the
controls. I haven't accessed the resistor block in order to change
it yet, so that could still be at fault. Is it easier to access it
from the cab, or from outside by taking off the covers?

Sorry for all the problems in my first post, but I'm desperate! :)