Some sort of main fuse..? Or something?
 

2002 S40.
Recent problem is that the heated seats, rear defrost, the map/overhead lights have all stopped working and the clock has stopped keeping time. It didn't work one night but everything worked again the next day but since have stopped working again. Also when I press the overhead light to the left the "open door" light on the dash lights up for some reason.
Is there some sort of main fuse that controls all these things?

Look at the fuse box lids for fuse locations for the seats etc.
It's clearly labeled.

Martin

You have two fuse boxes - under the hood and under the dash (near the hood release - the fuse puller is usually stored in the cover under the dash). After pulling the fuse you can probe for voltage etc with your multi-meter... You can also probe connectors - ie stick a paper clip into the back of a connector (where the wire goes in) without opening the connector. Look around for loose connections under the dash and under the seats as they sometimes can get kicked.

You can also look at the wiring diagrams for common junctions/connectors - intermittant problems problems typically point to connectors/weakened wiring (like in door or trunk jambs and sockets).

From the owners manual:

Fusebox, Passenger compartment
No. Components Amperage
1 Blower motor, ECC -25A
2 Cigarette lighter, Accessories 20A
3 Accessories, Power windows, Power mirrors 10A
4 ECM for DSA/ABS/CEM. 10A
5 Seat heating 20A
6 Illumination of switches: Winter, DSA back-up lights, CEM, Turn indicators 15A
7 Cruise control, Shiftlock, SRS, Alarm 10A
8 Hazard warning flasher, Central doorlock activated, flasher 15A
9 Audio system, Cigarette lighter, Accessories 15A
10 Wiper/Washer front 20
11 SRS, ECM for DSA/Engine/Transmission, Combined instrument panel, Immobilizer 10A
12 Sun roof, heater/AC, Alarm, Seatbelt reminder 15A
13 OBD II connector, Brake lights 15A
14 Front wiper, headlamp wipers, Wiper/washer rear 20A

Fusebox - Engine compartment
No. Components Amperage
1 Supply to fuses 11/2-10 (certain models) 120
2 Supply to fuses 11/B 1,2,8 and 13 40
3 ........... ...
4 ........... ...
5 Rear window and side-mirror heaters 25
6 Driver's power seat 25
7 ........... ...
8* ECC, courtesy lights, ignition lock, Siren, Combined instrument panel 10
9* Central locking, alarm 20
10* Audio 15
11 ECM for immobilizer. engine relays 20
12 Power windows, Power mirrors 30
13 Radiator fan 30
14 Starter motor, supply to fuses 11/B 3-7, 9-12 and 14 40
15 ABS 50
16 Reserve --
17 Fuel pump 15
18 Engine components 10
19 Foglights 20
20 Reserve --
21 High beam L 15
22 High beam R 15
23 Parking lights 10
24 Parking lights 10
25 TCM 10
26 ........... .....
27 Electric socket rear 15
28 Main light 15
29 Horn 15
30 Charger AC, fan AC 15
31 VAC pump (AT) 10