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I just got a 2001 Civic EX and installed a new head unit in it (Sony MEX-BT3000P) and now randomly the hazards and the cluster will flash in unison, and eventually stops. Does not seem to be connected with operation of the HU as messing with it doesn't really cause it. It usually happens when you start the car. Could this be me mis-wiring the HU? The previous owner also has an aftermarket security system installed which I can't seem to figure out. There is a switch that was installed next to the Cigarrette lighter. Flipping it doesn't seem to do anything. If anybody has any suggestions they would be much appreciated.

 
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Did you connect the orange wire? If so you got lucky because it usually fries the entire electrical system. Disconnect it.

 
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Nope! Did not connect the dimmer or illumination wires, I did my homework. I figured out the problem, it was the aftermarket alarm. I just put it in valet mode and it stopped (had to go to manufacturers website). I do have a question about the ground wires though: should I use both the ground from the HU and the ground from the harness? Or just 1?

 
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I'm not entirely sure but I can't see having both connected causing any problems.