Easy to be wrong

[Danglerb]

For months the front speakers on my wife's car have been cutting in and out, both of them at the same time. I had a top local shop do the work, but they are a top local shop, busy, need appts, and can be expensive, so I've been dragging my feet about taking it in since it could be some part of the system they have no responsibility for. I haven't been doing anything myself since the install is buried under interior panels in the trunk. Climbing into the trunk and removing a bunch of panels has been too low on my priority list, but I took a swing at it the other night.

First round I couldn't get the stereo to not work, so not much I could test, voltages look fine, connections solid.

Two or three rounds later it is not working consistently, so I put my son in the front seat to listen to the speakers and start checking stuff. Power, ground, and control voltages look fine, so I start messing with the input signal wires. Factory radio head is speaker level and maybe not ground referenced, so there is a little box that converts to RCA and adjusts level. Crimps from speaker wires to box are solid, RCA from box to amp also seem fine, but when I move the box the sound cuts out.

Bingo, move the box, sound cuts in and out, box is very much the installers baby, so off I go today to show them their mistake and get it fixed. Shop guy is skeptical, am I sure both speakers work? Many times people think both work, and when one stops working they think both have stopped (different class of failure indicating different items in the chain). Finally he is willing to come out and take a look, sure enough, move the box and sound cuts in and out.

Now I get my education, very carefully he isolates the motion to just one segment of the signal chain. Wiggles the crimped speaker output wires from the head unit to the level box, wiggles just the wires going into the box, just the RCA connection out of the box, and finally the RCA connection into my amp. Its my amp, and for some reason I am sure will be obvious when I open it up, wiggling just one of the RCA inputs makes the sound cut out.