Steering wheel controls for an aftermarket head unit in a '98 Buick LeSabre

Man, it's been a while since I posted. Been working on a few interesting projects, just haven't had the time to write them down. Nonetheless, here's one that turned out pretty good.

I recently purchased a new (to me) '98 Buick LeSabre LS, so I immediately began fixing all the random crap in it that bugged me. Luckily, this was the exact same model as my old car so I've gotten pretty good at working on them and have a ton of spare parts lying around.

Namely I had an aftermarket Pioneer DE-UHxxxx something or other head unit I wanted to put in because as we all know listening to the radio sucks. However, this time I wanted to keep the steering wheel controls functioning. Partly because I'm lazy but also because I've hit NEXT so many time on that radio I'm afraid that the button is wearing out!

In this case, there are 8 buttons on the steering wheel that run directly to the stock LeSabre radio and control VOL+, VOL-, SEEK+, SEEK-, TEMP+, TEMP-, SCAN+, SCAN-.

As seen in the diagram below, these commands are all sent to the radio over a single wire, which then interprets them based on the resistance of the connection. And in the case of TEMP+ and TEMP-, passes them along over a serial connection to the climate control unit.

All 8 switches are in parallel and the resistance progressively increases as you move from right to left. Power is sourced from power distribution cell 10 (12VDC), passes through several fuses, the steering wheel connections (note that the "Inflatable Restraint Steering Wheel Module Coils" are not really coils, but in fact rotary electrical connectors) then back and into the radio wiring harness via a light green wire. This is confirmed by the radio diagram which lists the purpose of each wire:

The one we're interested in is Pin E6 LT GRN which is listed as the Remote Control Signal. This can be further confirmed by checking the aftermarket wiring harness (where it dead ends as it isn't used for anything) with a multimeter. When these buttons are depressed, it should read a resistance between this wire and power (found going through a 2A fuse under the steering column) similar to the one above, depending on which button is pressed (they will differ slightly due to tolerances). When I tried this, I read the following values:

Button	Resistance (Ω)
VOL+	1.293k
VOL-	1.586k
TEMP+	1.932k
TEMP-	2.409k
SEEK+	3.131k
SEEK-	4.303k
SCAN+	6.830k
SCAN-	13.790k

Meaning everything is working as expected.

But how does this translate into useful commands on the new Pioneer radio? Luckily, most aftermarket radios have a remote input that works similarly to the one in the stock LeSabre radio. It too, is capable of reading resistances and issuing commands based on those resistances. And luckily, these resistances have already been figured out here: http://jvde.net/node/7

Now, if you wanted to do a REALLY nice job, you could open up the steering wheel and swap out all those resistors. Or, like most people you could buy an interpreter (like this) and set it up to read the existing resistances and correlate them to the desired outputs. However, neither option was attractive to me. Opening the steering wheel is too much work. And the interpreter costs $50, takes up space, and introduces added complexity and potential lag into the controls. Therefore I chose option 3.

Option 3 is using the existing resistances in the circuit to issue commands to the radio. Now, the downside to this method is you will only get a limited range of commands, some will likely be duplicated, and they won't map to the correct buttons. But, since I mainly just wanted volume and track controls and only I will be using the car, none of that matters to me.

So, I went ahead and added a 7.5k resistor in series with the steering wheel controls like so:

 

This shifts the measured resistances to the following:

Button	Resistance (Ω)	Pioneer Command
VOL+	8.793k	SEEK+
VOL-	9.086k	SEEK+
TEMP+	9.432k	SEEK-
TEMP-	9.909k	SEEK-
SEEK+	10.631k	SEEK-
SEEK-	11.803k	SEEK-
SCAN+	14.33k	VOL+
SCAN-	21.29k	VOL-

Meaning that I was able to achieve all 4 of the commands I wanted, with minimal effort and 0 expense (assuming you have the resistors lying around).

Your mileage may vary depending on what resistances are used in your make and model and what commands you would like to keep.

After a few weeks of use I'm glad to say it works very reliably with almost no lag. I was even able to re-purpose the old 12VDC wire to power a dashcam, since it turns on whenever the ignition does. Score!