Where do i ground my vm9215bt

First things first my friend. You must test the gage to be sure it is good. Normal procedure is: Switch off, unplug the wires from the sending unit at tank, connect jumper between the power wire and ground wire in the connector block, go to the switch and turn it to run position. If the needle goes to full, the gage is good. Turn the switch off. Now, be sure the connection is plugged in completely and you've a GOOD ground on the sending unit tab on the top of sending unit. No ground, no working needle. Use the test light to find if there's continuity with ground tab using power wire and touch the ground. No light, work with it till you do. Clean stuff to make the ground on tab work. Once test light does light between power and ground tab, your good. Gage should definitely be working now. If it doesn't work, this calls for replacing the sending unit in tank by dropping the tank first. Then it's easy to replace the sending unit.

From all electronic spare part selling shops. An easy to get replacement part, indeed.

Here is a quick video tutorial for Model VM9725BT.
https://youtu.be/kNHDkZu4pos

I got pretty frustrated until I finally found the option. Hopefully it is in a similar spot.

Are the fuses okay? With the ignition switch off, you could hook up a temporary wire from the chassis of the car (the outside metal part of a cigarette lighter is a good ground) to the backside of the radio. Once secured, you can try the stereo again.

Just ground the wire for the parking brake to anywhere on the frame of the car.

Most amplifiers have a common color code to hook them up. On your head unit, there should be a blue wire. That is your amp. Turn on lead. The positive + symbol goes to your battery +. And that lead is usually red. Your negative terminal - is this symbol and the wire s usually black. That either goes to the - side of the battery or grounds to car chassis. The sound inputs to your amp. either by RCA cables or high speaker level input. That depends on your amps. set up. If you have any questions, post back and I'll try to reply by next day or two.

Did this work? none of the codes (543210 / 1264) work for me. I dont want to hardwire it.

Too many subdirectories is most likely the problem.

The stereo may have limitations like 8.3 standard. That means a file can only be 8 characters long with a 3 character extension. Or 256 for folders, including paths. This is old school naming restrictions.

If your head unit powers off at high output it could be several things.
1. check ALL your grounds (head unit, amp, etc..)
2. it could be a a short.
3. head unit could be defective

disconnect the amp power/signal and see what hapepens.
If it doesnt happen you probably have an open ground or short in your amp power or signal cables. Amp could be defective but that is unlikely

If it still dies when the amp is disconnected it is isolated to your head unit. Check your head unit's ground/power/fusing or swap in another head unit to eliminate wiring faults.

Good Luck!

12/29. I actually figured this one out myself after reading posts concerning parking brake over rides. It turns out that the Boss BV9055 will not powerup if the pink parking brake wire from the units wiring harness is not grounded. Once I grounded that pink parking brake wire the unit did power up.