My Volvo (2002) uses CANBus to monitor various lamps (I assume its current that's monitored). I intend to splice into one of the headlamps and one of the sidelamps and use those live feeds to dim (sidelights) and then turn off (headlights) the DRLs.

Would going via a 1k resistor to the transistor's base cause any problem with the monitoring? I'm kind of assuming it would be quite a high impedance(?) so not be 'noticed'.


  • 3
    Instead of verbal description of what you are trying to do, post a schematic.
    – Nick Alexeev
    Sep 18, 2015 at 23:27
  • I'm having a lot of trouble understanding just what you're asking. Do you think that, by monitoring the headlight voltage, you can tap into the CANBus? If not, how do you expect to "tap into" and control the lights?
    – WhatRoughBeast
    Sep 19, 2015 at 3:31
  • DRLs - daytime running lights?
    – timbo
    Sep 19, 2015 at 22:01
  • Why are you trying to do this? If all you want is to disable DRLs, just ask someone with VIDA to do it for you. It's a configurable option. You attach the laptop with VIDA interface to the car switch the option in software. Anyone with VIDA will do it in less than 10 minutes. Sep 21, 2016 at 18:47

1 Answer 1


Just grabbing the first 2002 Volvo Replacement Headlamp I could find the headlamps run at 12V/65W, meaning it would draw 5.4A of current. If you hooked up a 1k resistor and ran it straight to ground while the lightbulb was on, that resistor would pull 12mA of current, adding an additional 0.2% load to the battery.

From the car's perspective, you'll be fine.

  • 1
    Just out of curiosity, why was this moved? I really feel like it belongs in the EE stackexchange.
    – Adam
    Sep 19, 2015 at 21:59

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