Wire the radio Dash buttons to the aftermarket stereo (Thanks to Nyeark)
Standard disclaimer: You can blow up your head unit, speakers, amps, subs, and car if you screw up doing this. It’s hard to do so unless you’re really not reading this and/or don’t know what you’re doing, but still, you’ve been warned.
Quite a few people have complained that after putting in an aftermarket head unit, they’re unable to use the dash-mounted radio buttons. If you don’t mind taking apart your head unit and know how to solder, you can change this, and adapt your dash buttons to work with your new radio.
On page 80 & 81 of the owner’s manual, you should find (assuming all the manuals are the same; mine is from a ’91 coupe) the wiring diagram for the radio. If your manual is different, simply look for the “Audio and Power Antenna” pages of the electrical (EL) section. Located on this page is the pinout and wire-color-scheme for the dash buttons. I don’t have a scanner, so I recreated the appropriate harness in Illustrator.
The wire numbers, colors & functions are as follows:
1 – Black – Common Ground
2 – White w/purple stripe – RADIO ON button
3 – Gray – SCAN button
4 – White w/red stripe – AM/FM button
5 – White w/blue stripe – VOL. UP button
6 – White w/green stripe – VOL. DOWN button
7 – Green w/white stripe – ILLUMINATION (I think this is the illumination 12v hot)
8 – Black w/purple stripe – ILLUMINATION (I think this is illumination ground)
This mod isn’t too hard, but it’s somewhat complex and even harder to explain, which makes it sound hard, so I’ll try my best to outline it here. Post any questions you have and I’ll do my best to answer’em.
Okay, the way the dash buttons work is as follows: each button has a 12v wire, and there is a common ground for all the buttons. Pushing the button closes a switch, and connects the common ground to that button’s 12v wire, thus completing the circuit and actuating whatever the switch’s 12v wire goes to.
The way my head unit worked, and hopefully yours too, is this: each button was a type of electrical switch called a ‘tactile switch’. I’ve provided a picture below so you can see if your HU uses these. Although they have more than 2 legs, there’s only 2 sides to these switches. One of them will be connected to the radio’s 12v hot, the other to ground. You will have to discover for yourself which goes where by following the traces on the PCB (printed circuit board). If you can take a decent picture up close of the PCB, I may be able to assist you in this.
Examples of Tactile switches
Some tips on trying to find out yourself: if you find the trace on one leg ‘meeting up’ with traces from other parts of the radio (not other switches), and eventually ending up in a large area, this is probably ground. 12v traces will typically go from a power source straight to the leg, and will not ‘meet up’ with any others. However, your unit may be different, so take these tips with a grain of salt.
Anyway, once you figure out which leg on your switches is hot and which leg is ground, write it down somewhere. It’s easy to forget and annoying to go have to look it up again. Another tip: if the switches have a characteristic that lets you distinguish one side from another, (i.e., a notch at the top, so you can tell left and right), then all the switches will typically follow the same convention. Meaning, if you look at two or more switches and both have the left-leg(s) as 12v and the right-side leg(s) as ground, then all the others will probably follow this convention, saving you some time.
Assuming you’re still with me, here’s the gist of the mod: connect the 12v hot of the dash button to the 12v hot of the HU switch you want it to actuate when pressed. Then connect the ground of all of the HU switches you used to the dash button’s common ground.
To do this, solder a wire to each side of each HU switch (try to use color-coding; red=12v hot, black=ground – you dont have to use those colors, of course, but that’s the standard). This is the most tedious part of the mod, because tactile switches are very small and hard to solder to. I’d recommend picking up a dead HU to practice on before attempting it on yours. Use long wires for the 12v hot sides – each one of these wires will need to travel outside the casing of the HU and connect up to the dash button harness, and you want extra length so you can put strain relief, so the wires don’t tear off the tactile switches. Once you’ve got all these wired up, bring all the ground wires together and solder the free ends together to another (long) length of wire of the same color. Only this one ground wire will travel outside the case. Note: BE SURE to label each wire’s function (radio on, vol up, vol down, etc.) so you know where to connect it later on! If you forget to do this, you’ll have to open the case back up and risk tearing the wires. I’d recommend either mailing labels cut in half or masking tape to label the wires.
Once your soldering is all done and your wires are all ready, apply electrical tape generously over any exposed wire (except the ends that will be outside the case, of course) and over the solder points. You should also apply hot glue to the solder points, if you can, as it makes for great strain relief and also insulates. You need to do this so 1) you don’t short anything out (this could fry things) and 2) so you don’t tear the wires off the solder points (this could damage the tactile switches, which would mean you could not repair the mod, and could also render that button useless, and also fry things).
Thread the 12v wires and the single ground wire outside the casing of the HU. You can cut a hole to do this, or do what I did and route it up through the ventilation holes.
Now you’re past the hardest part. Set the HU aside for a moment and go remove the dash buttons and the wiring harness for them. You can do this by pushing on the buttons from behind them (you’ll need to have your radio removed to do this, of course).
If you want to, you can replace the bulbs that illuminate the dash buttons with LEDs for brighter light and a different color (or if they do not illuminate because they’re burnt out), but that’s outside the scope of this guide. PM me or post here if you want instructions on this.
The wiring harness for the dash buttons has two sides. One side plugs into the buttons, the other plugs into the factory radio. Cut the harness that is on the factory radio side (it should only have 6 wires). Using the wire coloring I outlined earlier, label each wire with its function, and then grab your HU again.
Here you get a choice: you can either solder each wire together, or put on a connector. I chose quick-disconnect crimp-on connectors to make it easier to remove the HU (and easier to connect a new one should I ever redo the mod). If you choose the connectors, crimp one on each wire, making sure that all the HU wires are one gender and all the dash button wires are the other, then connect them together. If you choose to solder them together directly, do so. Whichever way you go, once finished, wrap up the junctions with electrical tape to prevent shorts & disconnects.
And now you are done with the electrical work! Go reinstall everything in the car (you will need to unplug the wiring harness on the dash-button side to reinstall the buttons, and then plug the harness back in from the rear). Reinstall the HU, give it power, and then test each button. If they all work, great. If not, go check your wiring. Also flip on your lights to see if the buttons illuminate – if not, your bulbs may be burnt out and need replacing.
I hope I’ve done a sufficient job in explaining this mod and hope some of you get some use out of it. If anything needs clarification, let me know and I’ll try to sort it out.
Credit – Nyreak