Older Kenwood head units came with an infrared remote control and a built-in IR receiver. Good for van life, you can control the radio from the back.
Newer ones? You're out of luck. The stereo doesn't even have a built-in IR receiver.
But there's a way you can make it work anyway!
This is tested with a Kenwood KMM-BT508DAB / KMR-M508DAB (circa 2021). But it should work with many other models.
The loom coming out the back of your radio will have a blue/yellow striped wire. Probably labelled steering wheel remote control or similar. Luckily this wire accepts standard infrared remote control signals!
You need an infrared receiver of some kind. Some gadgets come with infrared receivers. Cut the cable off and use one of those, easy. Otherwise you'll need to get an infrared receiver module.
Infrared receiver modules are simple devices. They have three pins. +5V power input, ground, and infrared signal out. The simplest way to wire it is this:
+5V supply ----------------------------- Infrared +5V supply
Radio ground (black wire) ----------------------------- Infrared ground
Blue/yellow wire from stereo ----------------------------- Infrared signal out
But if you don't know the pinout of the infrared module, you'll want to add some protection components:
680 ohms
+5V supply ----\/\/\---------+---------- Infrared +5V supply
| +
10uF, 35V ---
---
| -
Radio ground (black wire) ------------------+---------- Infrared ground
Blue/yellow wire from stereo ----------------------------- Infrared signal out
The 10uF capacitor can be either ceramic or electrolytic.
If it's electrolytic, make sure you connect it the correct way around!
Stripe indicates negative
|
V
___________
/ \========\----
\__/________/---- <-- +
The resistor can be wired either way, it isn't polarized.
Where do you get the +5V supply from? Simplest option is the USB socket on the front of the stereo. Take a USB cable, cut it open. Red is +5V, black is the radio ground. Green and white can be snipped off.
Don't want to tie up the USB port? Use the circuit below:
680 ohms In +------+ Out
+12V from ignition switch ---\/\/\----+---| 7805 |---+---- Infrared +5V supply
(red wire into stereo) | +------+ |
+ --- | GND ---
10uF, 35V --- | --- 0.1uF, 35V
- | | |
Radio ground (black wire) ------------+------+-------+---- Infrared ground
Blue/yellow wire from stereo ----------------------------- Infrared signal out
7805 pinout:
_________
__/___o___ /
/ /|/
/ 7805 / /
/ / /
+-------+ / <- Metal face on bottom
|_/ / /_|/
/ / /
In | Out
GND
The 0.1uF capacitor is a ceramic type. The 10uF capacitor can be either
ceramic or electrolytic. If it's electrolytic, make sure you connect it the
correct way around!
So you've found an infrared receiver, but you don't know which three wires does what. First thing is to find the ground wire. If your infrared receiver has a jack plug on the end, ground is probably the contact closest to the plastic body of the plug. If you've cut the cable, check the cut-off end with a multimeter to see which colour wire goes there. There's a good chance the wire is either black or bare copper strands.
Now you can use trial-and-error to determine which way round the other two wires go. If it doesn't work, swap them over. The resistor and capacitor in the circuit protect the infrared module if you get it swapped the wrong way. Make sure you make the connections with the ignition turned off, then turn it on once everything is connected. If it doesn't work, turn the ignition off before changing it over!
If you know the pinout for sure, you can omit the 680 ohm resistor. Just replace it with a simple wire. If you're using a 5V supply from a USB socket, you can eliminate the capacitor too (but not if you're using the 7805 circuit).
Seems that Kenwood mostly use the same remote control codes over the last two decades. If it's a Kenwood remote control designed for a car stereo, it'll probably work. I tested with a KCA-R6A and it works fine. The tuner button works as a source button, there is no button labelled source on this remote.
Some universal remotes may work. Kenwood use the NEC protocol.
There are two power wires going into the stereo. One red, one yellow. The yellow one is connected to an always-on 12V source, and the red one is connected to the ignition switch. All the power used by the stereo is drawn from the always-on yellow wire. The red wire is simply a signal to tell the radio to wake up or shut down. It draws almost no current.
So you can use both the ignition switch and a switch at the back of the van to control the radio with two small low-current diodes:
1N4001 diodes
1A fuse |\|
Red wire from ignition switch ---o~o---------------| |---+----------- Red wire
|/| | to radio
Switch at back of van |
/ |\| |
+----o~o-------O O----| |---+
| 1A fuse |/|
|
Leisure battery +12V --o~o--+---------------------------- Yellow wire to radio
10A fuse
Other brands of head unit (Sony, Pioneer etc.) use different methods of remote control. Most commonly different value resistors on the remote control wire to trigger different functions. In this case you'll need to make a wired remote with switches and resistors.