Hi , help !
I just did the garmin upgrade from factory sat nav. I took it a step further by removing the speaker and mike from the garmin and extending the wires and positioning the mike on the right where the switches were behind some roof lining material and the speaker fitted really well where the Multi switch used to be on the left. My issue is the speaker sound is so tinny it's difficult to hear on Bluetooth calls. How can I get this sounding a little richer ?. Thanks, Alan

 

Try feeding the audio into some cheap amplified 12v speakers hidden under the dash such as:

Motorcycle Car MP3 iPod Amplifier 2 Speaker 180W 12V | eBay

You will really only need to use one channel. You might need to attenuate the signal from the Garmin with a couple of resistors connected as a resistive divider if the input level is too high and it distorts.