Car Stereos: Car stereo ford aspire, dc volts, digital multimeter

Question
QUESTION: i bought a dual, xr4110 headunit, and installed myself. it powers when key is in acc, it works. when i start the motor, it powers down. it wont tun on, though the power button is illuminated. whats the deal?

ANSWER: Hi Erik,

Any after-market head unit has two power connections:  one for constant power, and another for key-switched power.  It sounds to me like there may be a problem with the accessory power connection.

The easiest way to troubleshoot any power problem is with a digital multimeter, set for DC volts.  Pull the radio and test the red and yellow wires at the back, with then engine running.  You should measure around 12-14 volts, on both the red and yellow wires.  If both wires test with power, but the deck won't turn on, then the head unit is defective.  However, if you get a low or no power reading on one of the wires, then your vehicle has a wiring problem.

My suspicion is that your Aspire has a problem with the key switch.  The red wire behind the head unit is ultimately connected to the key switch accessory wire.  This wire should have voltage in the "ACC" or "RUN" positions.  It's possible for the switch to be defective in such a way that the wire is powered in the ACC position, but not in "RUN".  (One test would be to turn the key to the RUN position, without starting the engine, and see if the deck works then).  If the key switch is the problem, and you don't want to invest in a replacement key switch, then you'll need to find a different power source for the head unit's red accessory power wire.

Hope this helps!

Brian



---------- FOLLOW-UP ----------

QUESTION: Hey Brian, follow up. Ive swapped the yellow and red wires and now the unit runs when in acc and when the car is running. is there anything i should know, if there is something dangerous or damaging with this route ive taken

Answer
Odd that it should work one way and not the other.  Does the head unit turn off properly when you turn off the key?  If so, does it retain the clock settings and station presets when you turn it back on?  

There's nothing that will damage the head unit in reversing the constant and accessory power wires; but if they're not hooked up correctly, you'll lose your station presets, tone settings, and clock setting each time you turn the car off.

Brian