Rear speaker wiring issue.

[LukesCougar]

To clarify first.. i know little about wiring.. but the only way my rear speakers work is grounding out the positive..? Why would this happen.

Front speakers work fine, rears dont but i noticed it would play music if the wire made contact with the chassis specifically the postive cables?

I dont have a multimeter.. originally thought the speakers i had were blown but they all work just fine when grounded out.. even the ford oem ones i thought were bad.

 

[Grog6]

You either have killed half the out put chip in the deck, or you have a really weird deck. Measure the output voltage with a meter; if i says 6V, half the chip is dead.

 

[LukesCougar]

The speakers up front have plenty of sound, and the rear ones do to but only when i manually ground them. Just wiring them up to positive and negative theyre silent but second i ground them to chassis it works. It didnt seem like an issue with power but more of an issue with ground just not sure where it would be at because the deck is brand new and ive double checked that its hooked up properly.
I dont have a multimeter at the momment but will get one.

 

[LukesCougar]

the car did have premium sound.. so there should be an amp for the rear speakers in the trunk right? Could that have something to do with it. I did install an aftermarket head unit.

 

[Kidd-7]

I’m not familiar with the premium sound wiring so that could be the issue here.
The root cause here is there’s no return path back to the head unit for those speakers so when you touch the wire to chassis you’ve complete the circuit and thus sound.

 

[Grog6]

The amps in the trunk are BTL amplifiers; neither speaker wire is supposed to be grounded, and it will kill it to do that. Both wires are at half battery voltage, and move in opposite directions to make up tp a ~8V max signal to the speaker. This allow a amp to put out twice as much power as it would with only 12V. You can get a max of about 36 watts at clipping from a 12Vbtl amp, in a 4 ohm speaker. Now that car speakers have moved to 2 ohms, it can be a max of 12^2/2=72W. This is at clipping, so probably more than 10% distortion; it would sound awful at that level.
Real amps have switching power supplies to make more supply voltage. Doubling the voltage increases power by 4x.
My amp has +-120Vrails, so 120^2/4=3600Wmax, per channel! lol. it uses a different audio stage, that wastes more voltage, to prevent Distortion; not running "rail to rail" makes audio amps "hifi"amps, and drops distortion below 1%, which most of us will never notice.
Grounding a speaker wire in a 'bridged' system runs one of the rails to ground. assuming it doesn't immediately kill the chip, it's running 36W of dc power thru your speaker. That pop you hear when you ground it is the speaker moving all the way one direction, just like hooking a battery to it.
Don't do that, it will kill it eventually. You have something wired wrong, I'm guessing it's a wire at the deck/amp connection.
Both speaker wires for a channel should go the the two terminals of the speaker. Decks can be "differental" out, same as described, or they can be single ended, which uses ground for one wire. Amp inputs usually want the single ended signals, that's why there are converter boxes to add an amp to a stock factory system. If you run a speaker level signal into an rca input, it will sound really bad. Hope this helps!

 

[LukesCougar]

The amps in the trunk are BTL amplifiers; neither speaker wire is supposed to be grounded, and it will kill it to do that. Both wires are at half battery voltage, and move in opposite directions to make up tp a ~8V max signal to the speaker. This allow a amp to put out twice as much power as it would with only 12V. You can get a max of about 36 watts at clipping from a 12Vbtl amp, in a 4 ohm speaker. Now that car speakers have moved to 2 ohms, it can be a max of 12^2/2=72W. This is at clipping, so probably more than 10% distortion; it would sound awful at that level.
Real amps have switching power supplies to make more supply voltage. Doubling the voltage increases power by 4x.
My amp has +-120Vrails, so 120^2/4=3600Wmax, per channel! lol. it uses a different audio stage, that wastes more voltage, to prevent Distortion; not running "rail to rail" makes audio amps "hifi"amps, and drops distortion below 1%, which most of us will never notice.
Grounding a speaker wire in a 'bridged' system runs one of the rails to ground. assuming it doesn't immediately kill the chip, it's running 36W of dc power thru your speaker. That pop you hear when you ground it is the speaker moving all the way one direction, just like hooking a battery to it.
Don't do that, it will kill it eventually. You have something wired wrong, I'm guessing it's a wire at the deck/amp connection.
Both speaker wires for a channel should go the the two terminals of the speaker. Decks can be "differental" out, same as described, or they can be single ended, which uses ground for one wire. Amp inputs usually want the single ended signals, that's why there are converter boxes to add an amp to a stock factory system. If you run a speaker level signal into an rca input, it will sound really bad. Hope this helps!

There are radio wires that go to my trunk but i cant find an amp, unless its hidden under the carpet somewhere i havent looked. It almost looked like the factory amp had already been bypassed or its hidden but its 3-5 degrees here right now so i havent been outside the car looking around much or working on it.
I do have a multimeter so next time its a little bit nicer outside i can check for output and continuity check when the weather is a bit nicer.

 

[Grog6]

If you have premium sound, you had a small square plug that has the inputs to the amp. Amp is either under the radio, or under the rear deck, in the trunk. Yeah, fuck working on ANYTHING metal when it's that cold.
Hey, at least you wont drop the wrench, it'll be stuck to your hand, lol.

 

[LukesCougar]

If you have premium sound, you had a small square plug that has the inputs to the amp. Amp is either under the radio, or under the rear deck, in the trunk. Yeah, fuck working on ANYTHING metal when it's that cold.
Hey, at least you wont drop the wrench, it'll be stuck to your hand, lol.

Yeah damn right i changed the alternator when is was 4 ish degrees outside and had enough of working on the car for the day.. i still have yet to check voltage or do a continuity check but i do now own a multimeter! Just so i dont mess anything up i unhooked the rear speakers. When its a little warmer (wednesday is supposed to be like high 30s) im going to look around for a possible amp. If there is an amp is there any point in messing with it in the meantime? or can i just cut the wires at the deck for rear speakers and run new cables and bypass it? either way if my issue is being caused by a deck not operating with my radio or because of a short and lack of a full loop it would make sense to run new wires to bypass stock amp/ stock speaker wires anyways right?

 

[Grog6]

I put a heating pad on the bottom of the toolbox trays with rubber cement; they keep the tools warm, but you have to put them back in a lot.

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[LukesCougar]

The weather finally got nice enough to where i can work on the car a bit more. Now that i got a multimeter i found out pretty quickly wires are shorted. Nothing comes through the wires until i give it extra ground so gonna run new wires to the rears.

installed some schoche speakers up front just to test out because they were cheap and they have done me well in the past. The radio itself works just fine and with the new speakers it sounds pretty good vs the 28 year old premium ford speakers. Theyre not the best but its still a world of difference vs what was in it. Once i run new wires to the back i got more laying around to throw in. I will have to cleanup some wiring for the front speakers i borrowed one of my buddies strippers and theyre the dial adjustment ones.. took way too much wire off. Never used them until now so ill have to figure out how to adjust the thing correctly it was pissing me off. Ended up stripping too much off a negative cable and a positive cable on both sides . . so theyre crimped to the butt connectors by like 2 strands of speaker wire.. but they have solid connections just i wanna bet one bump breaks whats left of the wires. Forgive me lol id like to mention im a lot more mechanical than i am electrical