Hey guy,
I agree with Papajam, your horns are OLD and are no longer good. I would replace them with Ferrari FIAM air horns easily obtained from from Pep boys, or Auto Zone. They are really really cool, and let every one know you are there!!!!
As for your Heater, it is located under the dash in a very inconvenient place to work on. Basically to Repair/Replace the motor, you have to first remove the entire center dash and side panels. Then if that wasnt bad enough, You need a special elongated socket to get at the recessed bolts in order to free the plastic housing, Taking extra care not to disturb the vent slits. If you displace them...... it is a pain and a half to get them right again.
I have photos attached below for your viewing pleasure
I hope all goes well with your restoration.
Ciao Ciao
Martin.
71 Spider Veloce
87 Spider Quad.