GPS speed sensors are a popular way to drive a modern electronic speedo in an older Commodore, especially if your gearbox only has a mechanical speedo cable. But a GPS speedo is only as accurate as the signal it gets, and where you put the antenna makes all the difference.
What the antenna needs
- A clear view of the sky. GPS signals pass through glass and plastic but not metal. The roof, the dash frame and the firewall all block signal.
- Away from interference. Keep it clear of ignition leads, alternators and cheap USB chargers.
- Fixed in place. An antenna rattling around loose gives a jumpy reading.
- Watch out for tint. Some metallic window films and heated screens can weaken GPS signal.
Common mounting spots (and their problems)
- On top of the dash pad: great signal, but it looks like an add-on and the cable needs a hole.
- Under the dash or behind the cluster: tidy, but surrounded by metal – signal is often poor.
- Rear parcel shelf: works, but means running cable the length of the car.
- Outside on the roof: best signal, but needs a hole in the roof or a cable through the door seal.
The best spot: the dash speaker grill
The VB to VK Commodore has a speaker grill on top of the dash, close to the windscreen and right near the instrument cluster. Swap it for a grill with a built-in antenna mount and the antenna gets a clear view of the sky through the windscreen, the cable runs straight down to the cluster, and from the driver's seat it looks factory.
We make three versions, all printed in UV-resistant ASA:
- SAAS GPS antenna mount – suits the SAAS GPS speed sensor
- Haltech GPS antenna mount
- Holdcom antenna mount
Note: the original dash speaker has to be removed to fit the antenna grill. Most people running a modern stereo use door or kick-panel speakers anyway. If you want to keep the speaker, our factory-style grill replaces a cracked original.
GPS sensor or ESA-01?
A GPS sensor isn't the only way to get an electronic speed signal. If you'd rather read speed from the gearbox, see GPS speed sensor vs ESA-01 for the pros and cons of each.
Setting up
- Mount the antenna and run the cable to the cluster.
- Power up and give it a few minutes outside, away from buildings, for the first satellite lock.
- Calibrate the speedo against a known distance or a phone GPS app, following the gauge maker's instructions.
Running a RetroTech dash kit? The GPS speaker grill pairs perfectly with our VB–VK dash kits.