Road Glide banner

Head unit power oddity

530 views 5 replies 2 participants last post by  lonestardiver 
#1 ·
2011 FLTRU stock head unit.
I replaced an amp that had blown for the front speakers and now after putting the fairing back together the head unit stays powered on even though every thing else is powered off.

Is the head unit negative switched and I have something grounded against it?

Only connections to amp are main power (positive/negative), switched power to cigarette lighter, and speaker out from head unit. No wiring changes to head unit other than speaker out to amp.
 
#2 ·
Do you mean you can still play music with ignition power off ? Try pulling the cigarette lighter fuse .if the power on the HU goes out, the amp is your culprit.
 
#3 ·
With bike in “off”, the head unit is still powered but no controls, no amp, no sound, etc. I guess the amp may be backfeeding “ground” to the head unit through the speaker lines. I have yet to see a schematic to show how the head unit gets it’s power and whether the positive or negative is switched. If it is switched on the negative line then backfeed of the negative on the speaker ground makes sense. Which means I’ll need to consider a separate relay to control power to the amp.
 
#4 ·
You shouldn't have to do that, somethings not right. Your amp should shut down with the motorcycle's ignition.
 
#5 ·
The amp does shutdown with the ignition as expected.

I need to pull the outer off again this evening and see what I disconnect that reverts the situation. If there is indeed a “ground” connection between the negative power lead and the “ground” or negative speaker (input and possibly output) lines that could be interesting.

If that is doing it then it may require an additional relay.

The older amp (soundstream) didn’t do that. They wired up the same way.
 
#6 ·
Okay I have the mystery figured out.
The old amp was anodized and painted so the point where the bolts attached to the mounting plate were insulated.

The new amp is cast aluminum so there is electrical contact. The Negative line is grounded to the chassis. The mount being metal and attached to the metal brackets that the head unit attaches to allows for continuity from the negative to the radio all the time. It appears the radio is switched on the negative side so it allowed it to power the head unit. Nothing else was on so the only clue was the display.

So at this point I will be adding a relay for the negative line to the amp to resolve this.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top