The speaker level input on my Kenwood amp has only 3 wires... L+, R+, and a wire that is supposed to go to the radio chassis ground.

Behind the drivers kick panel I can access the rear speaker wire pairs.
Can I just use one of the grounds from one of the speaker wire pairs to connect to the chassis ground input on the amp?
Or do I connect the grounds from spkeaker -'s to the chassis ground input on the amp?
Or will I have to actually get to the radio. I assume it would be located behind the touchscreen? It isn't a conventional DIN type radio.
A more expensive solution would be to get a speaker level to line level converter, but that would be a last resort.

Thanks for any help

 

Do not use the speakers - supply wires for any chassis grounding or you will likely burn out the head units output amplifier. Wire it as the Kenwoods directions say and just use the + leads for the input signals and a dedicated ground line to the head unit's chassis for the input signal ground.

 

Do not use the speakers - supply wires for any chassis grounding or you will likely burn out the head units output amplifier. Wire it as the Kenwoods directions say and just use the + leads for the input signals and a dedicated ground line to the head unit's chassis for the input signal ground.

Ok, so this weekend I removed the radio, which was actually very easy to do, and found that the radio chassis is in fact connected to the vehicle chassis. So following instructions in the installation manual, it would have me connecting the + leads from the R & L speaker and a wire from the radio chassis (also the vehicle chassis) to the ground input to the sub amp... this seems wrong to me.

 

The people who design these things tend to have a pretty good reason for showing how they hook up the way they do.

Mostly with running a dedicated input ground line from the amplifiers audio inputs to the head unit is to help eliminate ground loop noises like alternator and motor whine and clicking sounds in the speakers due to lights and other electronic loads cycling on and off that can cause ground voltage variances between the head unit and the amplifiers internal input ground reference point.

Connect it as shown and don't worry about it.

 

It makes PERFECT sense.

In automotive amps it;s typical that R+ is 180 degrees out of phase with R- and the speaker is NOT connected to ground.
This is called bridging. So, a typical car channel is a low resistance speaker and runs with an EFFECTIVE +-12V power rail.

In a home amp, usually L- and R- are connected to ground.

To raise the power, you have to lower the resistance of the speaker or raise the supply rail. When you say have a 100 W car amp, it behaves like a non-bridged home amplifier.

See: https://en.wikipedia.org/wiki/Bridged_and_paralleled_amplifiers