BCM and Ecm locations - 1992 Oldsmobile Toronado

Question edited for clarity.
Question moved to model category.

The BCM is located behind the glove box. Open Glove box, empty contents, grab sides of box and push inward a little bit and continue to open door. Once that's done there are 2 modules back there, #1 is ECM #2 is BCM, The BCM has a yellow clip on it.

https://www.google.com/search?q=2013+Ford+Taurus.+Where+is+the+location+of+the+BCM

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Question edited for clarity.
Question moved to model category.

The BCM is located behind the glove box. Open Glove box, empty contents, grab sides of box and push inward a little bit and continue to open door. Once that's done there are 2 modules back there, #1 is ECM #2 is BCM, The BCM has a yellow clip on it.

https://www.google.com/search?q=2013+Ford+Taurus.+Where+is+the+location+of+the+BCM

..

Could be the crank relay , contacts sticking . Located in the under hood fuse/relay box. relay # 55 .Or could be something more complex . Control module problem maybe. The ignition switch is a input to the BCM - body control module . When you turn the key to start , this sends a voltage input to the BCM , the BCM will then send a message on the GMLAN serial data network to the ECM - engine computer which will energize the crank relay sending voltage to the starter .
Circuit Description (Key Start)
When the ignition switch is placed in the Start position, a discrete signal is supplied to the body control module (BCM) notifying it that the ignition is in the Start position. The BCM then sends a message to the engine control module (ECM) notifying it that CRANK has been requested. The ECM verifies that the transmission is in Park or Neutral. If it is, the ECM then supplies 12 volts to the control circuit of the crank relay. When this occurs, battery positive voltage is supplied through the switch side of the crank relay to the S terminal of the starter solenoid.

You would need to know how Body electronic's an serial data network's function .

The body control system consists of the body control module (BCM), communications, and various input and outputs. Some inputs, outputs and messages require other modules to interact with the BCM. The BCM also has discrete input and output terminals to control the vehicle's body functions. The BCM is wired to the GMLAN High speed serial data buss and the GMLAN Low speed serial data buss and acts as a gateway between them. If the BCM does not communicate the vehicle will not start due to the inability of the engine/powertrain control module (ECM/PCM) and vehicle theft deterrent (VTD) control module to communicate without the BCM providing the gateway function.
Suggest you take your vehicle to the dealer or someother qualified repair shop.

It wouldn't be a ground problem If it were the whole instrument cluster would be dead . Checking the BCM an the IPC for DTC'S - diagnostic trouble codes is the proper way to diagnose this type problem . Not worrying about grounds .
Odometer
The vehicle odometer is calculated and stored electronically in the body control module (BCM) and is sent via the serial data circuit to the instrument panel cluster (IPC) for display. The BCM calculates and stores the mileage based on the vehicle speed serial data information from the PCM/ECM. The IPC displays the season odometer information from the BCM in the driver information center (DIC). The odometer will display error if the IPC detects an invalid odometer data from the BCM. After an invalid odometer data is received from the BCM, the IPC will display the last known odometer reading for 1.5 seconds before error is displayed in the DIC.
Speedometer
The instrument panel cluster (IPC) displays the vehicle speed based on serial data message from the body control module (BCM). The BCM receives vehicle speed data from the PCM/ECM via the serial data circuit. The speedometer will default to 0 km/h (0 mph) if:
• The PCM/ECM detects a malfunction in the vehicle speed sensor circuit.
• The BCM detects a loss of serial data communications with the PCM/ECM.
• The IPC detects a loss of serial data communications with the BCM.

Your best bet would be to take it to the dealer !

Automatic Door Lock Operation
This BCM controlled feature can be personalized to driver preference.
The BCM will automatically lock the vehicle doors if the following conditions exist:
• All vehicles doors are closed.
• The ignition is in the ON position.
• The vehicle is shifted out of PARK.
The BCM will then unlock the doors when the ignition is placed in the OFF position. The body control module (BCM) monitors the signal circuit of the cruise control switches. The BCM relays the cruise control switch status to the engine control module (ECM) via the GMLAN serial data circuit. The ECM uses the status of the cruise control switch to determine when to capture and maintain the vehicle speed. The ECM monitors the vehicle speed signal circuit in order to determine and the desired vehicle speed. The ECM uses the throttle actuator control (TAC) motor in order to maintain the vehicle speed. For further information on the TAC system, refer to Throttle Actuator Control (TAC) System Description for the 2.2L (L61) engine or to Throttle Actuator Control (TAC) System Description for the 2.4L engine. Ignition voltage is supplied to the cruise control switch from the 2-amp EPS fuse located in the integrated BCM fuse block.
You should have the BCM checked for DTC'S

Are you talking about the radiator cooling fans ? If so there is no fan sending unit as you call it ! The fans are controlled by the BCM/PCM !
The engine cooling fan system is controlled by the body control module (BCM) and the powertrain control module (PCM) or engine control module (ECM). The BCM performs the calculations as to how long, when and what speed the cooling fans should turn on. The BCM then sends a class 2 message to the PCM/ECM to engage the cooling fan relays. If there is a malfunction with the BCM, the PCM/ECM will control the engine cooling fans independently. The engine cooling system consists of 2 electrical cooling fans and 3 fan relays. The relays are arranged in a series/parallel configuration that allows the PCM/ECM to operate both fans together at low or high speeds. The cooling fans and fan relays receive battery positive voltage from the underhood accessory wiring junction block. The ground path is provided at G100.
The BCM and PCM/ECM command Low Speed Fans on under the following conditions:
?€¢
Engine coolant temperature exceeds approximately 106?°C (223?°F).

?€¢
A/C refrigerant pressure exceeds 1 310 kPa (190 psi).

?€¢
After the vehicle is shut off if the engine coolant temperature at key-off is greater than 140?°C (284?°F) and system voltage is more than 12 volts. The fans will stay on for approximately 3 minutes.

The BCM and PCM/ECM command High Speed Fans on under the following conditions:
?€¢
Engine coolant temperature reaches 110?°C (230?°F).

?€¢
A/C refrigerant pressure exceeds 1 655 kPa (240 psi).

?€¢
When certain DTCs set.

The BCM is located behind the glove box.Open Glove box, empty contents, grab sides of box and push inward a little bit and continue to open door. Once that's done there are 2 modules back there, #1 is ECM #2 is BCM, The BCM has a yellow clip on it

The BCM is located behind the glove box.Open Glove box, empty contents, grab sides of box and push inward a little bit and continue to open door. Once that's done there are 2 modules back there, #1 is ECM #2 is BCM, The BCM has a yellow clip on it and I think 5 connectors, make sure you mark down the location of where the connectors go for reassembly. Whatever you are doing make sure your BCM is the culprit because the BCM rarely ever goes bad on these cars.

can't find exact location for you but here is a link to a caddy forum , someone there will know
1990 Deville BCM ECM communications problems Cadillac Forum Enthusiast...

I'm not 100% positive about a 1992 Toronado, but on my 1986 Toronado the BCM is behind and to the upper left of the glove box, and the ECM is behind the right side kick panel in front of the door. GM had a habit of moving them around from year to year.