1990 - 1995 Cadillac Seville STS Stereo Replacement

By: Pepsi2185

Safety

Exercise caution when working around electronics and unless you are well versed in automotive electronics DO NOT USE A TEST LIGHT. Although many times it is harmless to use a test light, in only takes one poke to destroy a 5 thousand dollar body controller.

Identification

There are three systems in use for a Cadillac sound system. The first is the conventional as described in 85-89 deville. In the dash is the stereo and tape deck.

The second is the cadillac car stereo controller is in the dash board and the sound system is amplified by a separate amplifier. It can also in rare occasions be a combination of controller amplified and separate amplifier. Meaning the stereo runs so many speakers and the amplifier will run the other. This system can either be interfaced into or totally bypassed.

The third is the dash board unit is a display. All sound processing and amplification are done in a trunk mounted module either behind the rear seat or next to the power antenna. Interestingly enough the controller still uses the same harnesses as all 90-late nineties GMs just is in the trunk at the controller. Antenna, speaker leads and power connections must be connected here.

Tools

• Socket set
• Wire connections tools
• Screwdrivers
• Panel removing tools

Materials

• Wiring harnesses
• Dash kit
• GM antenna adapter (prior to about 88 you will not need this)
• Crimp caps or electrical tape

Procedure

First System
Look along the woodgrain trim piece around the stereo for two bolts along the upper edge, if they are there remove them, if not just remove the trim. Remove the stereo.

Remove the metal sleeve from the aftermarket stereo with enclosed keys. Assemble the dash kit according to the dash kit instructions for the model year. You will need the dash kit piece which offsets the stereo 1.5 or so inches beyond the point at which the old stereo sat and it will stick out a bit. Insert the ring into the dash kit assembly and bend back the appropriate metal tabs.

Connect aftermarket stereo harness and wiring harness wires verbatim. Connect the bare ends together. Black to black, red to red and so on. There may be some that are not used such as orange with black etc. Tape those connections off. Don't forget the blue wire or the power antenna will not go up.

Plug in the harness to the aftermarket stereo along with the antenna adapter and the dash harness and clip stereo in to the metal sleeve. Install the stereo into the opening and reinstall the trim ring.

Second System
Remove the dashboard surrounding the stereo. Eldorado's and STS's remove the ring around the stereo, pull up on the woodgrain around the shifter and remove the screws that may be below the stereo. Be careful, yes its real wood! Remove the metal sleeve from the aftermarket stereo with enclosed keys. Assemble the dash kit according to the dash kit instructions for the model year. You will need to figure out if the system is completely amplified or partially amplified. Most of the time it is just the four channels on the amplifier.

Normal amplified All four channels are run by amplifier. With your harness to incorporate into the factory system, get power, ground, ignition, illumination, and power antenna/amplifier lead from here.
Constant (yellow)
Turn on (Red)
Ground (Black)
Power antenna/amplifier turn on (Blue)
Illumination (orange)

The four channels have to have a low level signal put into them. Instead of directly connecting the purple, green, white, grey and purple/black, green/black, white/black, grey/black to the speakers you have to either connect the RCA's behind the stereo to the input of the amplifier as a low signal input. Or you need to use a premium sound interface. Bear in mind without the adjustable interface you will get a popping noise as you change channels and sources. Either the the two front speaker in inputs share a negative signal and the rear speakers share a signal ground or have separate positive and negative signal inputs. If you look at the harness coming into the stereo and there are:

brown/yellow - left rear - green green/black
drk blue/blue - right rear - purple purple/black
green/lt green - front right - grey grey/black
tan/grey lining up - front left - white white/black

If the harness lines up as above you will have separate low signal positive and negative. If you have the factory harness with a naked wire with shielding over it in between two wires you have the shared ground system. Connect the positive wires to their respective colors in the harness for positive, but either share the negative or have a separate negative. You will need to compare your harness to the vehicle plug to tell which negative to go to. Example. Grey is front right and white is front left. Either grey with black or white with black is going to the be the negative signal lead for both front speakers. Same for the rears. Connect your harness, length of wire and aftermarket stereo harness all together matching colors verbatim. Just make sure you connect the input signal properly. Make sure you connect the blue wire at the harness or the amplifier will not turn on.

Combination For those of you with the lucky combination system, you will either have to connect the system half low signal input as described in the amplified section of system 2, or completely rewire the stereo in the vehicle. If you wish to rewire, watch your ohm load. New stereos can only handle two ohms. Speakers are as follows:

brown/yellow - left rear - green green/black
drk blue/blue - right rear - purple purple/black
green/lt green - front right - grey grey/black
tan/grey lining up - front left - white white/black

where brown, drk blue, green, tan, is positive - green, purple, grey, white is positive

Subwoofer Systems If you have some of the newer systems with subwoofers, it will take some testing with a 1.5 volt alkaline battery, low voltage input into the wiring harness and 12 volts to turn on the subwoofer amplifier. Sometimes the subwoofer input is connected in with the other four channels but most of the time it will have its own separate plug behind the head unit.

Third System
Remove the dashboard surrounding the cadillac car stereo. Eldorado's and STS's remove the ring around the stereo, pull up on the woodgrain around the shifter and remove the screws that may be below the stereo. Be careful, yes its real wood! Remove the metal sleeve from the aftermarket stereo with enclosed keys. Assemble the dash kit according to the dash kit instructions for the model year. The kit may take some custom work as these kits are rare and a supplement is sometimes needed.

Nonamplified system - Run the wires from the controller box located either behind the power antenna or behind the rear seat behind the control center. It is the box that has a coaxial cable coming into it. Usually you can trace the speaker wires to the box. Plug in your GM harness and run the wires to the front of the vehicle.

This system simply requires you to lengthen all of the wires 20 feet longer. Except for ground which you can connect to solid metal in the dashboard area. Grounds are very important, make sure your connection is a secure ground.
Antenna
Constant (yellow)
Turn on (Red)
Power antenna (Blue)
Purple and stripe, green and stripe, white and stripe, grey and stripe (all speakers)

Connect the wires from the aftermarket stereo harness to the vehicle harness adapter verbatim including the extension to lengthen the wire. Tape the bundle every so many inches for strength.

Amplified system - Run the wires from the controller box located either behind the power antenna or behind the rear seat behind the control center. It is the box that has a coaxial cable coming into it. Usually you can trace the speaker wires to the box. Plug in your GM harness and run the wires to the front of the vehicle.

This system simply requires you to lengthen all of the wires 20 feet longer. Except for ground which you can connect to solid metal in the dashboard area. Grounds are very important, make sure your connection is a secure ground. The only change is instead of directly connecting the purple, green, white, grey and purple/black, green/black, white/black, grey/black to the speakers you have to either connect the RCA's behind the stereo to the input of the amplifier as a low signal input. Or you need to use a premium sound interface. Bear in mind without the adjustable interface you will get a popping noise as you change channels and sources. The two front speaker in inputs share a negative signal and the rear speakers share a signal ground. Connect the positive wires to their respective colors in the harness for positive, but share the negative. You will need to compare your harness to the vehicle plug to tell which negative to go to. Example. Grey is front right and white is front left. Either grey with black or white with black is going to the be the negative signal lead for both front speakers. Same for the rears. Connect your harness, length of wire and aftermarket stereo harness all together matching colors verbatim. Just make sure you connect the input signal properly. Make sure you connect the blue wire at the harness or the amplifier will not turn on.
Antenna
Constant (yellow)
Turn on (Red)
Power antenna and amplifier (Blue)

In either system, run the extension harness up front to behind the dash where the stereo will go. Assemble the kit and put the stereo in the kit. Plug in the stereo and test. It may take some custom work to the get the cadillac car stereo to sit right and a little tacky window sealer to hold the stereo trim ring into place.

NOTE: This is in no way a cut and dry install. This is a bit of a complicated install and may be a challenge for one not acquainted with electronic stereo systems. The cadillac car stereo kit will take some creativity and custom work with a regular GM kit.