Changes to stock cooling system

Afternoon all.

The previous owner of my 460 turbo made some modifications to the radiator fan - he had it hardwired to a big red button on the dash! So I've spent the afternoon returning this eyesore to stock, and I've got a few questions.

1) The fan is kicking in and out what appears to be normally now. Any other turbo owners have overheating problems? Should I get a lower rated thermostat?
2) The temp gauge still doesn't work. The Haynes destructions are as useful as ever, saying the sender is on the 'left side of the block' (as seen from the drivers seat). There are two likely looking candidates - one with a square red plug with a metal retaining clip (more on the front left of the block), and another one actually on the left end of the block with a small round black plug. Which one is the sender to the gauge, and what resistance should I be getting?
3) While reconnecting the radiator thermostat I notice another piece of home made wiring - from one of the horns to +ve. I also found the stock factory plug. Plug in the stock plug, and no horn. I've checked the fuse and it's good. Help?

Thanks!

[Chris1Roll]

The second plug, i.e. the one on the end of the head, is for the info centre/temp guage.
I have no idea about resistance, however, it earths through the head, so would be a ood idea to check someone hasn't fitted it with PTFE tape.
Incidentally, the other plug you mention is also a temp sensor, two in fact, for the ECU. One wire goes to each ECU and it also earths through the block.

Regards,
Chris.