PAC 541GM21 Wiring Interface Instruction Manual

Cables for replacing Factory head unit.

Installation instructions for cables on list “A”

The “A” cable, is used when replacing a factory radio. (the appropriate cable from list “B” is also required). One end of cable plugs into or connects to your new aftermarket head unit and the other end plugs into the 18 pin connector of the OEM-1. When using the complete OEM-1 system the radio will be current protected by the vehicle fuse. The installer must decide to transfer any other fuses or noise filters from the harness provided with the head unit. Use the wire / terminal identification chart below to locate the correct power wires. The low level inputs are for radios up to 25watts x 4. While every effort has been made to insure this cable was made to connect properly to your aftermarket head unit, changes in models and configurations do occur. To prevent potential damage consult your stereo’s owners manual and check wire function (as shown below) with that of the head unit you have. Move any wires that are not in the correct pin location for you head unit.

Installation instructions for cables on list “B

The “B” cable, is used when replacing a factory radio. (the appropriate cable from list “A” is also required). One end of this cable plugs into the vehicle dash harness that was removed from the factory radio. (the AMP-UNV harness must be spliced into the vehicle harness, use the 16 pin chart below for wire identification) The other end plugs into the 16 pin connector of the OEM-1.
WIRE AND TERMINAL IDENTIFICATION
Output of the OEM-1, 16 pin connector (cable “B” or AMP-RCA). Looking into connector / wire side of cable.

Input of the OEM-1, 18 pin connector (cable “A” or “C”). Looking into connector / wire side of cable.

Cables for adding or replacing factory amplifier.

Installation instructions for cables on list “C”

The “C” cable, is used when replacing or adding aftermarket amplifiers to a factory amplified system. (the cable model # AMP-RCA is also required) This cable plugs in between the factory radio and the dash harness that was removed from the factory radio. The 18 pin connector then plugs into the OEM-1. The factory system remains unchanged using this cable. The ADD-UNV cable is used for universal connection to the vehicle harness for vehicles not listed. (splicing required) Audio should be at a low level when using this cable.
Use the AMP-RCA cable connected to the 16 pin connector of the OEM-1 to connect your aftermarket amplifier. The AMP-RCA provides 2 pair of female RCA jacks and a remote turn on lead.

Installation instructions for the AMP-RCA cable

This cable is used when replacing or adding aftermarket amplifiers to a factory amplified system. (the appropriate cable from list “C” is also required) The AMP-RCA cable connects to the 16 pin connector of the OEM-1 and provides 2 pair of female RCA jacks and a remote turn on lead for connection to your aftermarket amplifier.

If the rear speakers do not work, ( usually this not the case), when replacing the head unit, or the rear channels do not work when adding an amplifier, your vehicle may have only one Bose amplifier and use one common audio return.
To correct these problems: (do this only if the rear speakers do not work)
Cable AMP-GM21; connect the gray/black wire and green/black wires together.
Cable AD D-G M21; connect the white/black wire and green/black wires together.
1990-1996 Corvette. Locate the 21 pin connector at the receiver box behind the right seat below the storage compartment.

PAC Factory Amp Interface (FAI) – Level Setting

The Pacific Accessory Corporation® FAI is equipped with four channels of output level controls (gains) which should be adjusted for proper sound level matching.

• Start by setting each gain dial on the FAI at minimum, or fully counterclockwise.
• Turn on your car stereo and set the volume to roughly 3/4 of what the maximum number is. (Example: If a radio volume scale is 0-40, you would set the volume to 30 for this process.)
• Ensure that any equalizer or bass boost settings are flat or set to their default positions.
• Play a piece of music with a known frequency response that covers the entire audio spectrum. This is important for setting the gain accurately.
• Turn the gain control on the FAI up slowly until you hear distortion in the audio. Back off slightly from the point where distortion occurs. This is done by inserting a small flat blade or Phillips head screwdriver into the gain adjustment holes, located on top of the FAI.
• By turning clockwise, the gain for that individual channel, or the amount of sound allowed to pass through the FAI is increased. By turning counterclockwise, the gain for that individual channel is decreased.

The goal is to set the FAI gain high enough to get a clean signal but not so high that distortion is introduced. You will do this for all 4 channels.
Applicable devices as of November 2023.

541NIS2| ROEM-NIS2| PAC ROEM-NIS2 Interface Retains Factory amp in select Nissan
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541FRD2| ROEM-FRD2| PAC ROEM-FRD2 Interface Retains Factory Amp in select 95-02 Ford
541GM21A| ROEM-GM21A| PAC ROEM-GM21A GM Bose Interface, Select GM Models
541FRD1| ROEM-FRD1| PAC ROEM-FRD1 Interface Retains Factory Amp in select 88-00 Ford
541GM21| ROEM-GM21| PAC ROEM-GM21 interface Retains Factory amp in select GM
541NIS1| ROEM-NIS1| PAC ROEM-NIS1 Interface Retains Factory amp in select Nissan

© Crutchfield Corp 2023

ROEM-GM21
GM BOSE SOUND SYSTEM ROEM-GM21
Premium Sound System Interface
This interface will allow the replacement of.a stereo in the following GM vehicles with a premium Delco/Bose sound system. It is transformer isolated, maintains phase and is linear from 20 to 20,000 HZ. This 4 channel interface will allow the new stereo’s output to be adjusted to the input requirements of the existing factory installed amplifier, providing 2:1 gain and infinite attenuation. The output connector plugs directly into the factory harness. The color coded input wires are connected to the new stereo’s output harness.
For use with:
88-94 LeSabre, 88-93 CoupeDeVille, 88-93 Fleetwood, 88-91 El Dorado, 88-91 Seville, 88-93 Toronado, 88-94 Park Avenue, 90-95 Rivera, 90-98 Lumina, 90-97 Firebird, 90-97 Camaro Since 1976, when the 8-track player was the iPod of the day, PAC has been manufacturing high quality and rock solid mobile electronics interfaces that satisfy even the most demanding customer. Our patented and award-winning products deliver the performance and functional ity you want and deserve.
No matter what the challenge, our deep engineering and manufacturing knowledge and experience produce solutions you can count on!
Compatibility:
Tis product may have specific compatibility requirements to operate correctly in your automobile. Please consult a sales associate or visit www .pac-audio.com to learn whether or not your specific car and/or radio are compatible.
OEM-1 REV .10-23-02

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