Modern electronic speedometers – including the SAAS Muscle Series 3 and Muscle Digital speedos fitted to our RetroTech dash kits – need an electronic speed signal. Most classic Holdens only have a mechanical speedo cable, so you need a way to create that signal. There are two main options.
Option 1: SAAS GPS speed sensor and antenna
The SAAS SG31650 GPS speed sensor calculates ground speed from satellites and sends a pulse signal to your speedo. Nothing connects to the gearbox.
- Calibration-free – speed comes from GPS, so diff ratio and tyre size changes do not matter
- Quoted accuracy of 0.2% deviation, compared with 3–5% typical for cable drives
- First-time satellite lock in under 60 seconds and recovery from lost lock in under 2 seconds
- Simple wiring: power, ground and signal
Things to consider: it needs a clear view of the sky, so the reading can drop out briefly in tunnels, multi-storey car parks or the shed. Check with your local authority on the legality of using GPS as the only source of speed data.
Option 2: ESA-01 transmission to electronic speedo converter
Our ESA-01 screws onto the factory speedo cable output on compatible GM transmissions and produces a 12V square wave signal (16 pulses per revolution). No transmission modifications are needed.
- Works anywhere – no reliance on satellite reception
- CNC-machined aluminium housing with a waterproof locking connector and 2.7m wiring loom
- Connects with three wires: ignition 12V, ground and speed signal
- Your speedo is then calibrated for your diff ratio, gearbox and tyre size
For Trimatic, M20 and M21 transmissions, add the ESA02 cable adapter.
Which should you choose?
- Choose GPS if you want the simplest install with no work under the car, or you change diff ratios and tyre sizes often.
- Choose the ESA-01 if you want a signal that never depends on satellite reception.
Both work with SAAS electronic speedometers, and many other aftermarket speedos that accept a pulse signal. Find both in our gauge sensors and converters collection.
Not sure which option suits your car? Get in touch with your model, engine and gearbox and we will point you in the right direction.