I have a vehicle tracking unit (GPS + Telecom) which needs +12/24v DC supply.

The +12v battery red wire comes to this point where it gets split between the relays and a fat wire harness (which goes to the ECU and other parts of the fuse-box).

Is it safe to connect the power supply to the +12v relay supply of a vehicle (headlamp relay to be precise)? I've noticed this terminal is connected in parallel directly to the battery of the vehicle.

The tracking unit has a 3A fuse inside across the input line.The unit draws around 250mA power from the source.

2 Answers 2


Load wise you'll almost certainly be fine. 250 mA should be well within the design capacity of the circuit.

The other thing you'll want to consider is whether or not the circuit powers the tracker when you want it to. Is that circuit always hot? If so you may find the that the draw on the battery is more than you want (i.e., the battery gets drawn down between starts), as a "parasitic" load 250 mA is pretty big.

So, think about why you're installing the tracker and when you want it to be active. That will help you pick the circuit to tap into. Also, if you want it active all the time check to see if it has a "sleep mode" where it only comes on occasionally if the vehicle is powered down or isn't moving. That would make it much more battery friendly.

  • So when the tracking device is idle it draws around 20mA current and only when the vehicle is moving it does around 250mA when it sends data to the server which happens once every 2 mins provided the vehicle is running. Sep 22, 2016 at 7:34

Should be fine! On first reading of your post, I was thinking, "No, no, no... you have to have a protection fuse..." But since you do have a fuse across the input line, you should be just fine.

The voltage coming out of your battery is indeed 12 volts. And as for the 250mA, the average car battery's amperage is between 400 and 600A, so 250mA shouldn't make any difference whatsoever to any systems on the battery. That being said, any current draw will drain your battery, so be sure to turn off the GPS when the car isn't running.

  • The device draws around 15-20mA when the vehicle is idling/stationary/notmoving. Thanks! Sep 22, 2016 at 7:35

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