You can not. Speakers do not supply a voltage they need a voltage to operate correctly.
v=ir 12=i20 i = 0.6 Amp
Could be the relay or switch at steering wheel Check to see if there is 12volts coming from the fuse. If there is power (12volts)on both sides of the fuse, then it might possibly be the horn switch. Is there 12volts at the horn when the horn button is pushed?
One speaker not working:80% chance the wiring is disconnected or broken15% the speaker is damaged or electrically failed inside5% the stereo amp failed on that output onlyIf it is a SUB with its own amp and power supply look for out put from stereo and power supply as well as the list above.
Typically, the speaker cabinet is powered by the Amplifier. It's the amp that is raising the volume and power to make the speaker move. "Combo" amps have the amplifier and speakers in one box.
can't be done using just resistors
No, you need to supply the correct 18V to your speakers.
no, theres nothing there to amplify the guitar signal. ive plugged directly into the speaker cab and nothing happened
12Volts
You cannot increase voltage by adding amps.
No, it will short out. You can however expose it to water as in washing off an auto battery.
Check the fuse for the sunroof. if it is good check for power (12volts) at the motor when using the switch. if there is power most likely you'll need a motor if you have the means you can also put 12volts to the motor to see if it operates.
2/12volts batteries