Which fuse is for the instrument panel back lighting?

PH?NG KH?M CHUY?N KHOA TAI - M?I - H?
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Back lighting or warning lights ? check engine , ABS , air bags , seat belt , oil light etc... ?
Interior Lamps Dimming
The second group includes lamps which may be dimmed. This group may use a combination of vacuum fluorescent (VF) illumination and incandescent lamps.
• Power window switches
• HVAC control head assembly
• Radio
• The instrument panel cluster (IPC)
When the ignition switch is turned to the ON position, the vacuum fluorescent (VF) display (radio) turns on at maximum brightness. When the park lamps are ON all incandescent back lighting turn ON at the dimming level indicated by the IP dimmer switch. At the same time all vacuum fluorescent (VF) displays dim to match the indicated dimming level. When the headlamp switch is placed in the PARK position, the park lamp supply voltage circuit provides an input to the body control module (BCM). The BCM then supplies voltage to the instrument panel dimmer switch through the instrument panel dimming lamps control circuit. The setting of the instrument panel dimmer switch determines the amount of voltage that the instrument panel dimmer switch supplies to the BCM through the instrument panel dimming lamps low reference circuit. The BCM then sends a pulse width modulated (PWM) voltage to all the interior lamps. All the vacuum florescent (VF) and incandescent back lighting lamps are provided a specific voltage and are then grounded. When the headlight switch is turned to the PARK or HEADLAMP position, all incandescent back lighting turn on at the dimming level indicated by the IP dimmer switch. When the IP dimmer switch is moved from MIN to MAX, all vacuum fluorescent (VF) displays, as well as all incandescent back lighting respond from Minimum intensity to maximum brightness in response to the IP dimmer switch.

I would have it checked for DTC'S - diagnostic trouble codes stored in the BCM !
DTC B2624 Display Dimming Input Range/Performance
The body control module (BCM) supplies voltage to the instrument panel dimmer switch through the instrument panel dimmer switch signal circuit. The dimmer switch varies the voltage and returns the new voltage to the BCM through the dimmer switch signal return circuit. The BCM uses this voltage to determine the illumination level of the instrument panel lamps.

DTC B2625 Display Dimming Pulse Width Modulation (PWM) Output Circuit Range/Performance
The body control module (BCM) receives a variable voltage from the instrument panel (I/P) lamp dimmer switch. The BCM uses this signal in order to vary the illumination level of the I/P lamps. The I/P dimming lamps output from the BCM is a pulse width modulated voltage supply used to light the I/P lamps. If a malfunction occurs in the I/P dimming lamps output circuit, this DTC is set.

DTC B2662 Park Lamp Switch Circuit Malfunction
The park lamps are controlled by the turn/headlamp switch. Positive battery voltage is supplied to the switch through the EXT LP fuse. When the turn/headlamp switch is placed in the park or head position, battery voltage is supplied to the park lamps. The body control module (BCM) is also connected to the park lamp circuit to sense whether or not the park lamps turn ON when the low beam or high beam headlamps are turned ON. The BCM also uses the parklamp battery positive voltage to power the instrument panel (I/P) dimmer output circuit. If the BCM senses that the low beam or high beam headlamps are ON and the park lamp input is not active, DTC B2662 sets.
Do the park lamps work ?

The lights on the radio are dimmed with the instrument panel dimmer control so usually they are fed with a separate 12 volt signal that is separate from the main radio power. It may have a separate fuse but may not. If it's not a fuse it could be a loose connector going to the radio, assuming the rest of the instrument panel lights are working correctly. I suppose it is also possible that the dimmer control has two sections, one for the radio and one for the panel lights, and the section for the radio is bad. Run the dimmer control back and forth stop to stop a few times, push on it etc. to see if that effects it. I suspect it is somewhere in the dimmer circuit.

Could be a bad wire possibly chaffing or grounding out to to another wire or frame. Check your fuses. You may want to pull the dash out and check that wiring as well

NEED RADIO UNLOCK CODE TO RESTORE RADIO
IPC INOP. SOUNDS LIKE IP CLUSTER IT'S SELF, COMMON ISSUE

Soldering the new bulbs in may have done something to the LH DIMMER MODULE ! The 10amp INT LPS fuse located in the I/P fuse box is good ? Is the dimmer switch at full bright ?
When the park lamps are on, battery positive voltage (B+) is supplied through the instrument panel (IP) fuse block INT LPS fuse via CKT 32 (YEL) to the dimming switch. The dimming switch supplies a variably controlled voltage to the dimmer module(s). The potentiometer in the panel dimming control cannot provide enough current in order to operate the panel lamps. The dimmer module(s) amplifies the current, supplying the variable voltage to the panel lights. As the amount of the current increases, the lamps become brighter. As the amount of the current decreases, the lamps become dimmer.
Buick
There is only 1 dimmer module that supplies current to the panel lights. The left dimmer module supplies current via CKT 8 (GRY) to the following components:
• The headlamp switch
• The door switch flood lamps
• The heater and A/C control
• The door handle flood lamps
• The passenger temperature control
• The ashtray lamp
• The shift select switch lamp
• The instrument cluster
• The steering wheel controls
• The reset switch
• The trip odometer
• The radio
Parade Dimming
The parade dimming feature prevents the dimming of the VF displays when daylight is sensed by the lamp control module (LCM) and the park lamps are turned on manually. If the LCM senses night time conditions and the park lamps are on, the LCM allows the VF displays to be dimmed.
All of the modules with the VF displays receive the dimming level from an input on CKT 8 (GRY) or CKT 1244 (BRN). When the LCM determines that the above conditions are met, the LCM sends a signal to the instrument cluster and the radio via CKT 390 (YEL). For Buick, the radio then relays this information to the heater and A/C programmer and passenger temperature control via CKT 724 (PPL/WHT). The modules with the VF displays then adjust the dimming level of their VF displays to match the level of the incandescent lights.
LH Dimmer Module
Under the left side of the IP, on the left side of the steering column brace

This color code works for 87-93 mustang factory radio; it might work on yours as well. I'm not sure if it has the same fuses though.

Radio Connector:

Light Green / Yellow - Hot at all times (Fuse 8)
Yellow / Black - Hot in ACC or Run (Fuse 11)
Light Brown / Red - Goes to instrument panel dimming rheostat (Fuse 4)
Red - Ground
White / Purple - Hot in ACC or Run (Fuse 11)

Speaker Connector:

White / Light Green - (+) Right Instrument Panel & Door Speaker
Dark Green / Orange - (-) Right Instrument Panel & Door Speaker
Brown / Pink - (+) Right Rear Speaker
Pink / Light Brown - (-) Right Rear Speaker
Pink / Light Green - (+) Left Rear Speaker
Tan / Yellow - (-) Left Rear Speaker
Light Brown / White - (+) Left Instrument Panel & Door Speaker
Orange / Light Green - (-) Left Instrument Panel & Door Speaker
Hope this helps.

Radios often have 2 fuses, 1 for ALWAYS ON, 1 for ACC. It's possible that the always on fuse may be blown, if the radio isn't asking for a code. I'm unfamiliar with your particular car but radios can sometimes have a fuse behind them as well as the one in the fuse panel.