Stereo Amp 12v Remote-On Wiring?

[takeyourmarx]

I have a smallish amp that i'm planning to use via bluetooth so I don't need a headunit.

Looking for suggestions on the best place to tap into to get a 12v signal that will power the amp on and off based on the key position.

Normally called remote on/off: it detects a hot 12v signal when the car is on, and when it goes cold, its turns the amp off.

I want to place this underneath the rear bench seat ideally, where getting power from the battery will be easy (battery is in the trunk).

But if the only solutions is to run it up the the front thats fine, in that case, what makes the most sense to tap into.

 

 

[bergie33]

There isn't anywhere in the back half of the car to pull that from. Best to use a splitting spade connector on the ignition, or maybe there is a connection under the dash. I know there is a grey/purple open connector near the steering column but I can't remember if that's constant 12v or switched.

 

Also, some of those Bluetooth adapters without a head unit have an amp remote trigger wire that turns the amp on when the Bluetooth is active.  It eliminates the need for a switched 12v from the car.

[Son of Marty]

On 12 fuse cars there's a 3 wire connector under the dash in it is a switched lead for the tii fuel pump tap off that.

[Mike Self]

You'll need to run a wire from a switched source that's hot only with the ignition on--there's one on the back side of the ignition switch--test with a voltmeter.   And if you have a 72-73 roundie or a 74 squarelight (not sure about earlier or later cars) there's an unused wire ending in an insulated female terminal that can be found under the extreme left end of the dash, in the vicinity of the turn signal and wiper relays.  It's the switched power source for a tii fuel pump and connects through fuse 11--at least on roundies.  From there you can run it down the side cowl panel and under the carpet edge and back seat to the trunk and your amp...

 

mike

[visionaut]

There’s also the factory connection for the radio - it’s a purple/white wire on the hazard button harness. It will supply +12V when the ignition is on (accessory and ignition)…

[John76]

2 hours ago, Son of Marty said:

On 12 fuse cars there's a 3 wire connector under the dash

Here's what that 3-wire connector looks like under the dash.

Connection 7-C is the green/white wire that is +12V only when the ignition is ON.

Connection 7-B is the Grey/white wire that is +12V only when the headlights/parking lights are ON.

Neither of these will provide power on the Accessory position of the ignition switch (R).

 

Here's how I would hook up your amp:

1) Run a wire from the female connector (radio plug) on the hazard switch to the back seat location for your amp.

2) Plug this new wire onto the #86 tab of a 4-pin 12v 30A relay.*

3) Run a 10 or 12 gauge red wire with an inline fuse from your trunk-mounted battery (+) to the #30 tab on the relay.

4) Use a 10 or 12 gauge red wire from the #87 tab on the relay to your new amp (+).

5) Find a good solid ground location under the back seat and connect to the #85 tab on the relay and your amp (-).

 

This will power your music system when the ignition is on the accessory mode (radio) and the driving mode (ignition on).

 

* Always good practice to use a relay on large power consumers e.g. power amps, fog/driving lights, big horns, etc.

 

#7 3-wire connector under dash. Not good for amp/radio.

 

 

 

[visionaut]

27 minutes ago, John76 said:

1) Run a wire from the female connector (radio plug) on the hazard switch

Ditto (just missing all the great additional wiring advice).

 

lol

[takeyourmarx]

Thanks all. Pulled it from the hazard switch/stereo (and put into the blue pictured below). It’s working well. I don’t have it into a relay, but the amp is fused up, maybe I’ll change it over eventually.

 

Also I need to sort out my horn, so I appreciate the diagram!!

 

 

[bergie33]

On 6/8/2024 at 2:49 PM, John76 said:

Here's what that 3-wire connector looks like under the dash.

Connection 7-C is the green/white wire that is +12V only when the ignition is ON.

Connection 7-B is the Grey/white wire that is +12V only when the headlights/parking lights are ON.

Neither of these will provide power on the Accessory position of the ignition switch (R).

 

#7 3-wire connector under dash. Not good for amp/radio.

 

 

 

 

 

John, do you have the legend that does with the under dash picture above to describe what each of the numbered items is?

[visionaut]

2 hours ago, bergie33 said:

do you have the legend

It was a PDF. He’s a master — diagrams and photos  - collect ‘em all!!

 

 

UnderDashRelaysPlugsandTaps (John76).pdf

[Redtail]

On 6/8/2024 at 4:30 PM, takeyourmarx said:

I don’t have it into a relay, but the amp is fused up, maybe I’ll change it over eventually.

Every car audio amp that I've ever seen has a built in relay so you shouldn't need an external one. 

 

The large fused power cable (constant 12v) that runs directly to the battery is where the amp will draw power while operating. The small switched 12v wire (remote) only turns the amp on and off with the ignition and doesn't see much power draw.

 

If you look at off-the-shelf amp wiring kits the power cable is often 2, 4 or 8 gauge and the remote wire is 14 or 16 gauge. They also never contain an external relay since it's redundant.

Edited June 10 by Redtail

[takeyourmarx]

52 minutes ago, Redtail said:

 The large fused power cable (constant 12v) that runs directly to the battery is where the amp will draw power while operating. The small switched 12v wire (remote) only turns the amp on and off with the ignition and doesn't see much power draw.

 

If you look at off-the-shelf amp wiring kits the power cable is often 2, 4 or 8 gauge and the remote wire is 14 or 16 gauge. They also never contain an external repay since it's redundant.

 Ok great yeah this what I thought and where my head was at. I can see how a head unit that uses the stock stereo wire to power the internal amp

might benefit from one. I’m just using that 12v spade as an on/off signal for the amp. Not to draw power to drive the speakers.