Will an Add-an-Ignition T-Harness Fit My Car?
An Add-an-Ignition T-Harness gives a car a switched ignition feed it does not have from the factory. It sits inline behind the 12V socket, so whether it fits your car comes down to one connector and one quick test. You can check both in about ten minutes with a torch, a circuit tester and your phone camera.
This guide is the fitment check. Still working out why your parking mode will not arm? Start with no ACC fuse and why dash cam parking mode fails in newer cars. Come back here once you know that is the problem.
What the harness actually does
Your dash cam needs to know whether the car is running or parked. It reads that from a switched accessory feed, the wire that goes live with the ignition and dead without it. On plenty of newer cars, including the whole BYD range, the interior fuse box is all constant power. No such feed exists in there to tap.
The harness is a Y-splitter. It unplugs the factory connector behind your 12V socket and sits inline between the two halves. It then passes a copy of that switched feed out to your dash cam or battery pack. The factory plug still does its original job. Nothing is cut, spliced or fuse-tapped.
That is also the key to the fitment question. The harness does not create a switched feed out of nothing. It borrows one that is already behind that socket. So the car needs two things: the right connector, and a socket circuit that genuinely switches with the ignition.
The cars we have confirmed
| Vehicle | Fitment |
|---|---|
| BYD Atto 1, Atto 2, Atto 3, Dolphin, Seal, Sealion 6, Sealion 7, Sealion 8, Shark 6 | Confirmed, all year models |
| BYD Sealion 5 | Rear 12V socket only. The front console socket is not a compatible fit. |
| Mazda CX-30 | Compatible. This is the one we get asked about most often outside the BYD range. |
| Anything else | Needs checking. See below. |
That last row is the honest answer rather than a cop-out. The harness is built around a 12V socket connector that is common across a lot of vehicles rather than unique to BYD. That is why the CX-30 works. But common is not universal, and we are not going to publish a fitment list we have not actually seen. If your car is not in the table, the check below takes ten minutes and settles it.
How to check your own car
1. Test whether the socket is actually switched
Do this first, because it is the test that rules cars out fastest and it needs no tools beyond a tester.
Put a circuit tester or multimeter on the 12V socket with the ignition on. Then turn the car off, take the key out, lock it and walk away for a few minutes. Test again.
If the socket has gone dead, you have a switched feed behind it and the harness has something to work with. If it is still live with the car locked and asleep, that socket is constant power. The harness then has no switched signal to pass through. Some cars also hold accessory power for a few minutes after shutdown, which is why the walk-away matters rather than just flicking the key off.
2. Look at the connector behind the socket
Ease the trim around the 12V socket with a plastic trim tool. You are looking for the factory plug on the back of the socket body, not the front of the socket itself. This is an in-dash job, not a dashboard plug-in.
Do not force anything. If the panel does not want to come away with gentle pressure, stop and check where the clips sit for your model.
3. Photograph it and send it to us
Take three photos: the back of the socket with the plug still connected, the plug on its own once unclipped, and a wider shot showing the trim you had to remove. Include your make, model and year.
Send those through our contact page and we will tell you straight whether it matches. We would rather talk you out of a part that will not fit than take the sale and deal with a return.
What makes a car a likely fit
From the cars we have seen so far, the pattern is fairly consistent.
- A front console 12V socket with a separate plug on the back, rather than a socket moulded into a larger assembly.
- That socket circuit switching off with the ignition, confirmed by the walk-away test above.
- Trim around the socket that comes away with a plastic tool rather than needing the console out.
Cars that tend not to suit have one of these three:
- A socket wired permanently live.
- A socket buried in an assembly with no accessible connector.
- An interior where reaching the plug means dismantling half the centre console.
In that last case the job is still possible. It just stops being a ten-minute DIY.
If it does not fit
You still have options, and none of them require giving up on parking mode.
- Run a switched feed through the firewall. There is usually a source in the engine bay. It means pulling trim and getting a wire through a grommet without compromising a factory seal. That is a job worth handing to someone who does it often.
- Fit a dedicated battery pack. Powers the camera from its own cell and leaves your starter battery alone. The better packs still want a switched trigger to charge sensibly, so check that before you buy.
- Book it in. We do not install cameras ourselves, but we keep a directory of independent installers and plenty of them have solved this exact problem before. They are independent businesses, so you book and contract directly with them.
Our guide to the no ACC fuse problem goes through each of those in more detail.
Fitting the harness
Once you know it fits, the install is short. Roughly 15 to 30 minutes for a confident DIYer, and the only tool you need is a plastic trim tool. No soldering, no crimping, no wire cutting.
- Remove the interior trim panelling around the 12V socket to reach the factory loom behind it.
- Unplug the factory connector and fit the harness inline. Factory plug on one side, your accessory feed passed straight through on the other.
- Run the switched output to your dash cam hardwire kit or battery pack.
- Refit the panelling and set your camera to parking mode. It now arms on ignition-off and disarms on ignition-on, by itself.
The constant feed and the earth still come from wherever you would normally take them, which on these cars is the easy part. It was only ever the accessory line that was the problem.
The harness is the BYD Add-an-Ignition T-Harness, and it works with dash cameras and dedicated battery packs alike.
Frequently asked questions
Does this plug into my dashboard?
No, and this is the most common misunderstanding. It connects behind the 12V socket, so some interior trim has to come off to reach the factory plug. Plug-and-play describes the wiring, not the access. There is nothing to cut or splice, but you do need to pull a panel.
Will it work on a hybrid or an EV?
The check is the same, because the harness cares about the 12V accessory circuit rather than the drive battery. The confirmed BYD list is entirely EVs and hybrids. Be more conservative with parking mode settings on these cars, since the 12V battery is usually smaller than a petrol car's.
Can I use it for a battery pack instead of a hardwire kit?
Yes. The harness supplies a switched signal, and a dedicated battery pack uses that signal to decide when to charge and when to run the camera. Check your pack's manual for which input it expects.
Do I need a fuse tap as well?
Possibly, depending on your setup. The harness solves the switched accessory feed. If your kit also needs a constant feed, that still comes from the fuse box. Our guide to which fuse to tap for a dash cam covers choosing it.
Is it reversible?
Completely. Unplug the harness, reconnect the factory plug to the socket, refit the trim. Nothing in the factory loom was cut, so there is no trace of it once it is out.
Not sure whether your car has the right connector? Send Michael or Harrison your make, model and year with a photo of the plug behind your 12V socket, and we will tell you. Talk to the Guys.
Last reviewed: 14 September 2026. The confirmed fitment list covers the vehicles we have checked ourselves as at that date, and it is not a complete list of every car the connector suits. We do not install cameras ourselves, so the access and fitting notes here are guidance for whoever does the work, and interior trim differs between models and model years. If a specification, a feature or a claim on this page is wrong or has gone out of date, tell us and we will correct it.
Commercial disclosure: The Dash Cam Guys designed and sells the Add-an-Ignition T-Harness described on this page, so read this as our own guide to our own product rather than an independent assessment of it. No brand paid for, sponsored or supplied anything for this guide. The fitment list, the install steps and the timing come from our own product documentation and from the vehicles we have checked. We have not published controlled measurements of current draw or parking-mode runtime for any camera used with it. We do not install cameras ourselves, so the access notes here are general guidance rather than a record of work we have done. If a specification, a feature or a claim on this page is wrong or has gone out of date, tell us and we will correct it.