Curcuit failure dash light reads circuit failure and seat belts/power door locks do not work

check your child lock circuit for failure

You might check the ignition switch or possibly a maxi fuse in the power distribution center.

FUSE PANEL LOCATION
The fuse panel is located in the engine compartment. A label on the inside of the cover lists the fuse amperage and circuits protected.
volvo 850 fuses fuse panel layout service repair manual
FUSE PANEL IDENTIFICATION
Fig. 1: Fuse Panel Identification
Courtesy of Volvo Cars of North America.
WARNING: Always disconnect battery ground cable before servicing "high-current fuses. It is recommended that "high-current" fuses be replaced by a qualified technician.
* 1 - 15 Amp
Fuel Injection, Distributor Ignition, Automatic Gearbox
* 2 - 15 Amp
Fuel Pump, Alarm System
* 3 - 10 Amp
Courtesy Lights, Oil Level Sensor
* 4 - Not Used (1993-95)
* 4 - 10 Amp (1996)
Electronic Start Inhibitor (Immobilizer)
* 5 - 30 Amp
ECC Blower (Speed 4)
* 6 - 25 Amp
Central Locking System, Alarm
* 7 - 15 Amp
Audio System (Amplifier)
* 8 - 25 Amp (1993-95)
Power Antenna, Trailer Connector
* 8 - 40 Amp (1996)
Electronic Start Inhibitor (Immobilizer)
* 9 - 30 Amp
ABS, Traction Control System
* 10 - Not Used (1993-95)
* 10 - 15 Amp (1996)
Heated Rear Seat (If Equipped)
* 11 - 30 Amp
Heated Rear Window & Side Mirrors
* 12 - 10 Amp
Brake Lights
* 13 - 15 Amp
Hazard Flashers, Headlight Flashers, Alarm
* 14 - 30 Amp
ABS, Traction Control System
* 15 - 10 Amp (1993-95)
Audio System, Courtesy Lights, Door Open Light, Trunk Light, Glove Box Light, Remote Control Central Locking System,
Oil Level Sensor, Seat Belt Reminder
* 15 - 10 Amp (1996)
Audio System, Courtesy Lights, Door Open Light, Trunk Light, Glove Box Light, Remote Control Central Locking System,
Oil Level Sensor, Seat Belt Reminder, Data Link Connector
* 16 - 30 Amp (1993-95) Accessories
* 16 - 30 Amp (1996)
Power Antenna, Trailer Connector, Accessories
* 17 - 10 Amp
Key Reminder
* 18 - 25 Amp (1993-95)
Heated Front Seats, Power Mirrors
* 18 - 15 Amp (1996) Front Fog Lamps
* 19 - 15 Amp
Left High Beam Headlight
* 20 - 15 Amp
Right High Beam Headlight, High Beam Indicator
* 21 - 15 Amp
Left Low Beam Headlight
* 22 - 15 Amp
Right Low Beam Headlight
* 23 - 10 Amp
Left Parking Light, License Light
* 24 - 10 Amp
Right Parking Light, Bulb Failure Warning Sensor
* 25 - 10 Amp
Rear Fog Lamps, Fog Lamp Indicator
* 26 - Not Used (1993-95)
* 26 - 25 Amp (1996)
Heated Front Seats, Power Mirrors
* 27 - 15 Amp
Back-Up Lights, Turn Signals
* 28 - 10 Amp
Cruise Control, Heated Rear Window, Seat Belt Reminder Light, Shiftlock, Bulb Failure Warning Sensor, Heated Rear Seat
* 29 - 15 Amp
ABS, Traction Control System
* 30 - 10 Amp
Cigarette Lighter
* 31 - 25 Amp
ECC, ECC Blower (Speeds 1-3)
* 32 - 10 Amp
Audio System, Remote Controlled Central Locking System
* 33 - 15 Amp (1993-95)
Power Seats, OBD Test Socket, Tailgate Washer/Wipe (Wagon)
* 33 - 15 Amp (1996)
Power Seats, Tailgate Washer/Wipe (Wagon)
* 34 - 25 Amp
Windshield Wiper/Washer, Horn, Headlight Washer/Wiper
* 35 - 10 Amp
Instrument Lights, Sun Roof, Traction Control System
* 36 - Not Used
* 37 - Circuit Breaker
Power Windows, Power Sun Roof
* 38 - Not Used
* 39 - Circuit Breaker
Drivers Power Seat
* 40 - Circuit Breaker
Passengers Power Seat
RELAY PANEL LOCATION
The relay panel is located at the left corner of the instrument panel.
i copied this off a volvo site Hope this helps

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You have a module that's going bad or is bad. Someone had either wrecked the car previously and didn't replace all damages modules. You can have a shop put on computer to tell you exactly which one needs replaced. There is one on the front of the vehicle one under drivers seat and one in with the seat belts those ate just sensors the actual modules are the site bags themselves

Take it back to the dealer .

Check the fuse and circuit breaker "A". I have the same problem except I am missing the circuit breaker. There was a circuit breaker that was jury rigged with some wires that worked for awhile until the wires broke.

turn key on --key off ---key on -- key off ---key on , then you should get the codes from the check engine light.

Power is supplied to the Power windows and sunroof through the power window circuit breaker. That circuit breaker is supplied power through the RAP (retained accessory power) Relay, the RAP relay also supplies power to the radio. The RAP relay is also fuse protected by the RAP fuse in the under hood fuse block. The RAP relay is energized by the BCM body control module.

The RAP relay is responsible for the radio and windows working after the igntion is turned off.

The first place to check would be the RAP fuse in the under hood fuse block and then the RAP relay in the Body fuse block.

A list of the BODY relay block located on the left side of the dash to the right of the interior fuse block is below:

(1) Park Lamp Relay (2) Courtesy Lamp Relay (3) Retained Accessory Power (RAP) Relay (4) Power Seats Circuit Breaker (5) Power Windows Circuit Breaker (6) Inadvertent Power Relay (7) Door Lock Relay (8) Headlamp Ground Relay (9) Driver Door Unlock Relay (10) Door Unlock Relay(1) Park Lamp Relay
(2) Courtesy Lamp Relay
(3) Retained Accessory Power (RAP) Relay
(4) Power Seats Circuit Breaker
(5) Power Windows Circuit Breaker
(6) Inadvertent Power Relay
(7) Door Lock Relay
(8) Headlamp Ground Relay
(9) Driver Door Unlock Relay
(10) Door Unlock Relay
(1) Park Lamp Relay (2) Courtesy Lamp Relay (3) Retained Accessory Power (RAP) Relay (4) Power Seats Circuit Breaker (5) Power Windows Circuit Breaker (6) Inadvertent Power Relay (7) Door Lock Relay (8) Headlamp Ground Relay (9) Driver Door Unlock Relay (10) Door Unlock Relay (1) Park Lamp Relay (2) Courtesy Lamp Relay (3) Retained Accessory Power (RAP) Relay (4) Power Seats Circuit Breaker (5) Power Windows Circuit Breaker (6) Inadvertent Power Relay (7) Door Lock Relay (8) Headlamp Ground Relay (9) Driver Door Unlock Relay (10) Door Unlock Relay

I’m happy to help further over the phone at https://www.6ya.com/expert/jeremy_69f3cc28d95bf514

check fuses for dash lights if you use a12 volt tester turn on runnig lights and check dash lite fuse for power the radio maybe on same curcit/