So I have the door speakers plugged into the radio and they work fine, but when I plug in the headrest speakers, the door speakers cut out and the headrest speakers don't work. As soon as I remove the headrest connector, the door speakers start working again. Anyone experienced this. I dug but couldn't find anything.

 

You have a radio in your car?

Seriously though, sounds like there is a short in the headrest speaker wiring. I'd check those out with an ohmeter.

 

I thought a short would cause a fuse to pop or the radio head unit(?) lights to dim (electronics is really not my forte). I looked for a short when it started happening but only traced the wires from the speakers until it got really messy in the dash. Might be easier to just run new wires under the carpet.

 

Unlikely.

The amplifier inside pretty much all modern-day audio equipment is internally current-limited, which is tantamount to short-circuit protection. This means that in the presence of an abnormally low-impedance load (which includes a short circuit), the amplifier's output is limited such that the voltage will drop to zero before the current exceeds a safe threshold. This is done to protect the amplifier, as all else being equal, a solid-state integrated amp will typically vaporize long before the fuse protecting it blows.



Might be easier, indeed.

If you have an especially sensative and well-calibrated ohmmeter, you can measure the DC resistance across the terminals feeding the headrest speakers at whatever point you're plugging them in. This is not a definitive test, as the nominal DC resistance is close to the impedance, meaning you'd expect to see a figure of somewhere in the vicinity of between 2 and 16 ohms (depending on the native impedance of the speakers and whether you've wired the driver and passenger seats in series or parallel), and values this low can be difficult to distinguish from zero (short) with cheap meters.

 

headrest speakers. lol.

speaker wires have power, but if they are grounded it doesn't necessarily mean a fuse will pop or HU go into protection mode. But you'd also expect to see some sparks in the least.