My auxiliary port has stopped working

No wonder you are having difficulty. Below offers the following opinions: 1) It is not on the passenger side foot well. 2) It is on the passenger side. 3) It does not exist. 4) You are really looking for the auxilary relay in the kick panel above the pedals. This is so laughable you are going to have to depend upon your lying eyes. My apologies in advance. I think part of the problem is that there was a change in the model in 1999 that is not picked up on in some sites. I will have to step back and let your own eyes find the truth of the matter. Below offers a lot of contradictions.

1999 MLs in the US did not have the aux fuse box in the passenger side foot well in spite of what you are told here: https://www.mercedesmedic.com/1998-2005-benz-ml320-ml350-ml500-fuse-box-location-diagram/ and in spite of what the manual says. Notice you don't find two plastic screws in the purported position.

The auxiliary relay panel is located above the lower kick panel above the pedals.

Maybe this will help: https://fuse-box.info/ The main fuse box: https://www.autofuseboxdiagram.com/35889-1999-mercedes-benz-ml320-fuse-box-diagram-2/ or https://www.carfusebox.com/mercedes-benz-ml320-1999-fuse-box-block-circuit-breaker-diagram/

Note that the following site proclaimes there IS NO auxilary fuse box. https://www.benzworld.org/threads/1999-ml320-auxiliary-fuse-box-location.3059219/ while MB MEDIC shows a picture of where it purportedly is on the passenger side!: https://www.mercedesmedic.com/1998-2005-benz-ml320-ml350-ml500-fuse-box-location-diagram/auxilary-fuse-box-location/

7-BATT MAIN 1
60A
Fuses: •
CIGAR/DLC/APO FRT
• CLUSTER BATT
• CTSY LAMP
• ON STAR
• PWR LOCK
• PWR MIRROR
• RAP RELAY
• RR PWR SCKT

look below for above listed componet's , pull those fuse's one at a time till arc stop's ,then you found your problem circuit . Do you know where the I/P fuse box is ?
Fuse Block- I/P
Right side of the I/P, in the right front door opening


Fuse Block-I/P Label
Fuse Block-I/P Application Table Fuse/Circuit Breaker
Rating
Description
BCM PRGRM
10A
Body Control Module (BCM)
ENHANCED EVAP/AWD
15A
Evaporative Emission (EVAP) Canister Vent Solenoid, Clutch Pump Check Valve
CIGAR/DLC/APO FRT
20A
Auxiliary Power Outlet-Front, Cigar Lighter, Data Link Connector (DLC)
CLUSTER/BATT
10A
Instrument Panel Cluster (IPC)
CRUISE
10A
Cruise Control Module (CCM), Cruise Control Release Switch, Cruise Control ON/OFF Switch
CTSY LAMP
10A
Body Control Module (BCM)
DRL
10A
Daytime Running Lamps (DRL) Control Module
HVAC/DIC/DRL/HEATED SEAT
10A
Air Temperature Actuator-Left, Air Temperature Actuator-Right, Daytime Running Lamps (DRL) Control Module, Driver Information Center (DIC), Mode Actuator, Rear Window Wiper/Washer and Multifunction Switch (Heated Seat Switch), Recirculation Actuator, Relay Block (Rear Window Defogger Relay)
ELC/TRAILER
25A
Auto Level Control (ALC) Air Compressor, Auto Level Control (ALC) Air Inflator Relay, Auto Level Control (ALC) Sensor
FRT HVAC HI BLWR
30A
Blower Motor Resistor Assembly
FRT WPR/WSHR
25A
Windshield Wiper Motor, Windshield Wiper/Washer Switch
HAZARD
15A
Turn Signal/Multifunction Switch
HEADLAMP
20A
Daytime Running Lamps (DRL) Control Module, Headlamp Dimmer Switch, Headlamp Switch
HTD MIRROR
10A
Outside Rearview Mirrors-Left, Right
HVAC/BLOWER
25A
HVAC Control Module
IGN1
10A
Body Control Module (BCM), Instrument Panel Cluster (IPC), Left Rear Side Door Actuator Control Module, Rear Object Sensor Control Module, Right Rear Side Door Actuator Control Module, Stop Lamp Switch
LH HEADLP HIGH
10A
Headlamp High Beam-Left
LH HEADLP LOW
10A
Headlamp Low Beam-Left
LH T/LP
10A
Tail Lamp-Left, Trailer Rear Wiring Harness
MALL/CLUSTER
10A
Body Control Module (BCM), Instrument Panel Cluster (IPC)
ON STAR
5A
Vehicle Interface Unit (VIU)
PASS KEY
10A
Theft Deterrent Control Module
PCM/ABS
10A
Electronic Brake Control Module (EBCM), Fuse Block-Underhood, Powertrain Control Module (PCM), Park/Neutral Position (PNP) Switch
PCM/CRANK
10A
Powertrain Control Module (PCM)
PCM/PASS KEY/CLUSTER
10A
Instrument Panel Cluster (IPC), Powertrain Control Module (PCM), Theft Deterrent Control Module, Instrument Panel Cluster (IPC), Powertrain Control Module (PCM)
PWR LOCK
20A
Body Control Module (BCM)
PWR MIRROR
10A
Outside Rearview Mirror Switch
PWR QTR VENT
10A
Auto Level Control (ALC) Air Compressor, Auto Level Control (ALC) Sensor, Rear Quarter Window Switch
PWR/HEATED SEAT PSD
30A
Driver Seat Assembly, Passenger Seat Assembly
PWR SLDG DR
30A
Left Rear Side Door Actuator Control Module, Right Rear Side Door Actuator Control Module
PWR WDO
30A
Window Switch-Driver, Window Switch-Front Passenger
RAP RELAY
10A
Relay Block (RAP Relay)
RH HEADLP HIGH
10A
Headlamp High Beam-Right
RH HEADLP LOW
10A
Headlamp Low Beam-Right
RR HVAC/TEMP CONT
25A
Air Temperature Actuator-Auxiliary, Blower Motor-Auxiliary, Blower Motor Relay-Auxiliary, HVAC Control Assembly-Auxiliary, Mode Actuator-Auxiliary
RR DEFOG/ HTD MIRROR
30A
Window Defogger Relay-Rear
RR FOG LP
10A
Fog Lamp Relay-Rear
RR PWR SCKT
20A
Auxiliary Power Outlet-Rear
RH T/LP
10A
Tail Lamp-Right, Trailer Rear Wiring Harness
RR WPR/WSHR
20A
Window Wiper Motor-Rear, Rear Window Wiper/Washer and Multifunction Switch
SIR
15A
Inflatable Restraint Sensing and Diagnostic Module (SDM)
STOP LAMP
15A
Stop Lamp Switch
SWC BACKLIGHT
2A
Steering Wheel Controls-Left, Right
T/SIG
10A
Turn Signal Switch and Backup Lamp Relay

Fuse Usage 1 Climate Control 2 (HVAC) 2 Compass 3 Ignition Switch, Theft Deterrent System Module (PK3) 4 Upfitter Courtesy Lamps 5 Climate Control 1 (HVAC) 6 Empty 7 Instrument Panel Cluster 8 Audio System, Chime 9 Auxiliary Park Lamp 10 Auxiliary Trailer Back-up Lamps 11 Remote Function Actuator, Tire Pressure Monitor (TPM) 12 Climate Control (HVAC) Controls 13 Trailer Park Lamps 14 Front Park Lamps 15 Taillamps, Back-up Lamps 16 Empty 17 Steering Wheel Sensor 18 Outside Rearview Mirror Switch 19 Empty 20 Empty 21 Rear Defogger 22 Outside Rearview Mirror Heater 23 Empty 24 Empty 25 Cargo Door Unlock 26 Rear Door Lock 27 Front Door Lock 28 Rear Passenger Door Unlock 29 Upfitter Park Lamps 30 Front Passenger Door Unlock 31 Driver Door Unlock 32 Airbag System, Automatic Occupant Sensing (AOS) System 33 Right Rear Park Lamp 34 Left Rear Park Lamp 35 Upfitter Auxiliary 2 (J-Case) 36 Upfitter Auxiliary 1 (J-Case) 37 Rear Blower (J-Case) 38 Empty (J-Case) 39 Run (High Current Micro) 40 Park Lamps (High Current Micro) 41 Empty (Mini Micro) 42 Upfitter Auxiliary 2 (High Current ISO Relay) 43 Retained Accessory Power (RAP) (High Current Micro) 44 Rear Defogger (High Current Micro)

It is a fused item. check all the fuses in the passenger compartment fuse box.

Instrument Panel Fuse Block
The instrument panel fuse block access door is
located on the driver side edge of the instrument panel.

Pull off the cover to access the fuse block.

The vehicle may not use all of the fuses shown.

Fuses Usage
1 Rear Seats
2 Rear Accessory Power Outlet
3 Steering Wheel Controls Back light
4 Driver Door Module
5 Dome Lamps, Driver Side Turn Signal
6 Driver Side Turn Signal, Stop lamp
7 Instrument Panel Back Lighting
8 Passenger Side Turn Signal, Stop lamp
9 Passenger Door Module, Driver Unlock
10 Power Door Lock 2 (Unlock Feature)
11 Power Door Lock 2 (Lock Feature)
12 Stop lamps, Centre High Mounted Stop lamp
13 Rear Climate Controls
14 Power Mirror
15 Body Control Module (BCM)
16 Accessory Power Outlets
17 Interior Lamps
18 Power Door Lock 1 (Unlock Feature)
19 Rear Seat Entertainment
20 Ultrasonic Rear Parking Assist, Power Liftgate
21 Power Door Lock 1 (Lock Feature)
22 Driver Information Centre (DIC)
23 Rear Wiper
24 Cooled Seats
25 Driver Seat Module, Remote Key less Entry System
26 Driver Power Door Lock (Unlock Feature)

It's not a fuse issue. Can you roll the window to the passenger side down with the drivers side panel? If you can then the control panel on the passenger side needs replaced. If you can't then the regulator/motor/tract for the window on the passenger side would need to be addressed.

On my 97 SL2 it's on the passenger front side near where your left foot would go. You remove the panel as part of the center console and it's behind it

In my 1994 Saturn SL1, there is a grey one under the hood on the driver's side AND one inside the car on the passenger side where the left foot would go


On the passenger side, on the side of the instrument panel, there is another fuse box, the radio fuse is number 10 on mine. The problem is I changed it and the radio still doesn't work.
On a 93 sl2 its in the same fuse box, but is number 19

All 3 are on separate fuses.

Cab fuse panel ( passenger side kick panel, by the fuel inertia switch ) :

Instrument panel power point : Fuse # 39
Rear Power point : Fuse #37
Cigar lighter : Fuse # 41

If you did not get an owners manual with your truck ( purchased used ), you can download one from Ford :
https://www.fleet.ford.com/maintenance/owners_manuals/default.asp

All 3 are on separate fuses.

Cab fuse panel ( passenger side kick panel, by the fuel inertia switch ) :

Instrument panel power point : Fuse # 39
Rear Power point : Fuse #37
Cigar lighter : Fuse # 41

If you did not get an owners manual with your truck ( purchased used ), you can download one from Ford :
https://www.fleet.ford.com/maintenance/owners_manuals/default.asp

Fuse for window regulator (circuit breaker) on 13 position auxiliary relay panel. The wiring connectors are located at the lower left and right side kick panels. The auxiliary relay panel is located above the lower kick panel above the pedals.

Headlight fuse location:
#18 High beam right 10A
#19 High beam left 10A
#20 Low beam right 15A
#21 Low beam left 15A

Daytime running light relay location on upper (auxiliary) relay panel. This are the only ones using relays regarding your question.

From April 1999
Position 7, Relay #173

Through March 1999
Position 8, Relay #173