MikkiJayne wrote: Thu Jun 18, 2026 5:17 pm Odd that this is even necessary, but glad it worked

I specialise in odd and unnecessary

Nice. Good job for reusing an old relay, its proably better made than whatever gets made today.

Correct although ultimately I would connect it to that adapter you bought as well (so relay output 87 going out to amp and adapter) to avoid speaker pops which will damage them over time. For testing purposes amp itself is enough.

You get a 5.99 relay from halfords:

https://www.halfords.com/motoring/tools/fuses-electricals-and-fixings/electricals/halfords-relay-12v-40a-4-pin-elec258-725494.html

connect ground from bose connector to pin 86 of relay
connect constant 12v from bose connector to pin 30 of relay
connect switched ...

what about using a relay? maybe leakage current of that switched ignition intended for bose is too much for the converter and the amp?

Thats it.
You can see the caps, voltage dividing resistors and 2 small transformers (one channel each) that will step down the signal at a cost of signal degradation, loss of deep bass frequencies and other things dependant on how its designed internally.

It should also have a small flat head ...

Connecting speaker ground to rca ground is a very bad idea, your amp may be damaged now.
High > Low converter as MJ suggested is probably the most economical workaround rather than rewiring the whole car.

link?

There is just one fill port thats accesible and everything can be done through it. Most cars have 2 and most mechanics have only seen cars with 2.

Your amp is incompatibile. Chassis ground and floating bose ground have difference in potential.

You could ground amp RCA to car's ground but then you'd end up with a massive pop sound each time you start the car which is not good for the speakers.

The solution i arrived at is to completely ...