The local classic car sales garage put me onto the 123 Ignition system some time ago. I hadn’t heard of them when I was rebuilding LGL but they were fitting them to all the vehicles that crossed their books with few issues. Easy to install, set up and maintenance free. They are available for 26 models of classic cars, so there’s something for everyone… even DAF!

I had originally replaced the Lucas D25 distributor with an electronic unit from Accuspark. It had its quirks (poor advance, retard tuning being one of them) but as a whole it worked fine and I was happy not to have to worry about burnt contact breakers etc (I’ve never had much luck with such things).

However, a chronic misfire and idle issue had started to occur earlier this year instilling a lack of confidence during the infrequent journeys I make. The normal troubleshooting for such things didn’t help.

I toyed with the idea of having the oringal Lucas D25 restored with electronic ignition but I noticed the body was actually cracked so there was little point.

The Parts

123 Ignition offer 3 flavours of ignition: Switch, Tune and Tune+.

“Switch” offering 16 different selectable ignition curves. This is the unit I have installed. The exact model name: GB-4-R-V-POS

“Tune” allowing the user to build there own ignition curve from two sets of data (static and advanced) this is handy if you need a distributor for a highly modified engine such as a vehicle used on the track.

“Tune+” is fully wireless and ignition curves are designed from scratch on an app and can be adjusted on the fly via Bluetooth. The app has a dashboard display providing, RPM, speed, voltage and temperatures and pressures of this and that. There’s even a Bluetooth immobiliser function.

The temptation of the Tune+ is obvious especially with the Bluetooth immobiliser function. But there were too many “what if” scenarios bouncing around in my head… imagine dropping your phone in the lake!

The simplicity of the “Switch” makes perfect sense for a simple vehicle.


The instructions to install the new “Switch” unit as super simple and clear. They go into sufficient detail. Not all of which I will repeat here.

First, disconnect the battery.

Before working on anything electrical on any vehicle, it’s good practice to disconnect the battery.

Next, ensure the rotor arm of the original distributor is pointing towards Cylinder No 1 (the one nearest the radiator)and the timing mark on the flywheel (or front pulley, depending on model) is roughly on the mark required.

For LGL, running on 98 Octane petrol this is 6 degrees Below Top Dead Centre (BTDC). This will give a reference point when setting up the 123 Ignition unit. (I’m not worrying about the presence of ethanol in modern petrol and its effect on ignition timing for this installation)

I find the easiest way to do find and align the mark on the flywheel is to remove the spark plugs and turn the engine with the hand crank until the correct position is obtained. (Removing the plugs will eliminate having to work against the cylinder pressure when turning the engine over by hand. It may add some backlash but this would be minimal)

6 degrees BTDC on the flywheel… slightly misaligned by the camera angle but it’s a tricky shot to line up!

It’s recommended to use a 3.2 ohm coil with the new distributor. I’d rather not take the chance the misfire was caused by the old coil so a new Bosch unit was installed.

Next the old Accuspark unit is removed and reverently packed away.

Side by side the two units look quite different. The “Switch” distributor has no counterweights in the bottom as all timing is purely electronic.

The timing and advance retard in the “Switch” is fully electronic, hence the lack of advance unit on the new unit. There is still a need for a vacuum pipe for the carburettor and this is accommodated with a spigot on the other side of the distributor.

Removing the 8mm Allen plug reveals the switch for the ignition curves. We’ll get to that at the end.

Now for the fun part…

Unit is pushed into the block. There’s a very positive engagement due to the large O-ring seal on the shaft and needs some pressure to push it home and engage with the drive dog. Note, the rotor is facing Cylinder No 1.

I don’t have any photos of the final set up as I was still suffering with acute dizziness at the time. It was enough working on the vehicle let alone getting decent shots.

The instructions cover line by line what needs to be done and the LED queue lamps makes it super easy.

There’s an additional wire on the “Switch” taking a feed direct from the ignition switch to power the electronics in the unit.

Fairly self explanatory. Assuming you’re working on a vehicle with an original (or decent replacement) wiring loom, the Blue wire will connect to the White wire from the ignition switch… but check first.

With the low voltage wires connected, new HT leads were made. The old ones would have been too short, give the new unit is slightly shorter in stature.

Curve Settings

To be honest, I struggled finding an optimal setting. The “Switch” is a replacement for most British 4 cylinder engined cars (one size fits all kind of thing) and although comprehensive ignition curve data is provided in the installation manual, I don’t know what it’s telling me and Land Rover have never published ignition curve data to measure it against.

As I don’t use the vehicle that much, working my way through each of the 16 settings would take an age and possible not do the engine much good.

I emailed 123 Ignition for guidance.. and their advice for the low compression Land Rover 2.25 petrol engine is curve “7” or “b”.

Closing Comments

That’s the unit installed. Pretty simple although it took near 3 weeks given the condition I’ve had. But it wasn’t time to start the engine just yet. I was also working on an SU Carb conversion 🙂

More on that in the next post.