Creating a switched Ground...
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Joined: Sep 2009
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From: NE Georgia
Creating a switched Ground...
Bought a head unit this afternoon for a great deal (link.
Only paid $450 for it brand new.
I've run up against an odd situation though. In trying to bypass the DVD/parking brake feature I've found that you can't simply ground the PB wire, it's looking for a switching -12v source, it can't stay grounded all the time. There are writeups online on using a physical switch to trick the unit, but I'd like something automatic. Here's my idea:
Use a relay to create this switching feature. Run it off of a 12v source that triggers in the truck is cut on, providing a -12v ground to the PB wire that goes away when the truck is cut off. This would give the radio what it needs, and keep things automatic. I've run normal voltage through a relay like this, but never a ground...will this work? What size relay? Is there a better way?
Only paid $450 for it brand new.
I've run up against an odd situation though. In trying to bypass the DVD/parking brake feature I've found that you can't simply ground the PB wire, it's looking for a switching -12v source, it can't stay grounded all the time. There are writeups online on using a physical switch to trick the unit, but I'd like something automatic. Here's my idea:
Use a relay to create this switching feature. Run it off of a 12v source that triggers in the truck is cut on, providing a -12v ground to the PB wire that goes away when the truck is cut off. This would give the radio what it needs, and keep things automatic. I've run normal voltage through a relay like this, but never a ground...will this work? What size relay? Is there a better way?
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Joined: Jun 2002
Posts: 10,511
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From: Under the flightpath of old ORD 22R
That would work.
The relay coil is setup like any other normal relay, and the normally open contacts ( pin 30 & 87 ) have ground to them, rather than power.
Pin 30 had a ground, pin 87 to the head unit.
I am guessing the trigger is a low AMP requirement, so any relay ( usually 20 A is the normal off the shelf size ) will be fine.
The relay coil is setup like any other normal relay, and the normally open contacts ( pin 30 & 87 ) have ground to them, rather than power.
Pin 30 had a ground, pin 87 to the head unit.
I am guessing the trigger is a low AMP requirement, so any relay ( usually 20 A is the normal off the shelf size ) will be fine.
