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Old 10-26-2015, 07:22 AM   #11
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Re: Stereo isolator

A plus to the relay option, is that it allows you to add the led LED indicator to tell you it is on house power. You could hook the LED to the output of the switch, but it would be on when either the van was running or it was switched to the house. It would be more of a power indicator, rather then switch indicator. In most cases this would probably be fine, although the accessory delay could make it confusing.

In theory you would use the relay option to minimize the length of wire, sportsmobile does not or didn't do this on mine, must have been 50 to 60 feet of wire for this mod as they originally did it.

The original SMB Radio switch does not change the always on power to the house battery. It does not sound like Boywonder's switch mod does either. You can move that input to your house battery also, if you were going to use a switch for it, you could use a make before break switch to not loose any power to the preset memory.


There are two other inputs from the Ford fuse panel; one unused and the other is for illumination.



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Old 10-26-2015, 10:07 AM   #12
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Re: Stereo isolator

Quote:
Originally Posted by Viva
That sounds slick. Is the "always on" wire that powers the presets/memory and etc. on the start battery? Or?
Quote:
Originally Posted by JWA
Most automotive-type radios have two power connections, one switched and one constant to the head unit which keeps memory and pre-sets alive.
Hi JWA,
It's the constant one I was asking about. I was wondering if BoyWonder moved that one to the house bank as well. I had the SMB "radio switch" in my '97 SMB, and it would drain the start battery if used a lot while camping. I guess from the constant on wire (?).

Now in my current rig I have sort of the "opposite" situation: A complete second stereo head unit was put in the "house" of the rig. Still, one of the power wires went to the start bank. I moved them both to the house bank, however, it's time to buy a new one and I'm really questioning the need for two separate stereos five feet away from each other. So thinking about going back to a more SMB style with just the dash radio, but powering it entirely from the house. I typically have plenty of house power for that, and if I lose presets when I (very rarely) turn off the house bank altogether, that's fine. Since I travel a fair bit, they are not typically set anyway. I usually have the house bank "on" when driving, so the dash radio would still function.

The downside is having to stoop into the cab to use the radio when parked, but it would likely have a remote, and too, with Bluetooth maybe I'd be controlling it with the phone somewhat.

Still, BoyWonder's setup is intriguing, and I'm still at the stage of planning/pondering, so I was thinking about if I'd want to set mine up that way vs. just purely house power. I just don't want it to be like my SMB radio that would drain the start battery when camping (on either setting). Maybe that was just messed up.[/quote]

Scalf: Thanks for the ideas on switching. I think my SMB originally had the same ~60' of wire, as I believe the radio switch was near the aft end of the couch. However the PO had moved it to right behind the driver's seat, so he could reach it from there. So I'm not positive he re-wired it same as SMB did, although probably. The PO's put the fear of God in me about even using the darned thing, so I rarely used the radio at all. However my buddy who bought it from me found that over a couple of days of camping and radio use, it would drain the start battery. We measured and yep, amp draw.

Quote:
Originally Posted by Scalf77


There are two other inputs from the Ford fuse panel; one unused and the other is for illumination.
I was just looking at this last night, because a friend put a head unit in the house section of his large RV. But it illuminates without that wire being connected. We were surmising that the purpose of it is to dim the display along with the dash lights if you have it hooked up (in a cab where you want that feature)?
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Old 10-26-2015, 10:13 AM   #13
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Re: Stereo isolator

Sorry, dup.
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Old 10-26-2015, 01:14 PM   #14
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Re: Stereo isolator

I am considering house power only for my dash stereo on an upcoming build. I too would love to hear if others have any concerns with that. I imagine you will have to turn the stereo off manually each time you leave the vehicle. I don't know if modern stereos rely on CAN bus info for speed dependent volume, reverse cameras coming on automatically, etc. Maybe you could still be on the CAN bus either way.
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Old 10-26-2015, 04:06 PM   #15
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Re: Stereo isolator

Quote:
Originally Posted by Viva
That sounds slick. Is the "always on" wire that powers the presets/memory and etc. on the start battery? Or?
Yes.

I don't see any reason why the "always on" power couldn't be provided by the house batteries. I've always assumed that the "always on" power was negligible, like keeping the preset memory alive, etc.

Alex.....you could certainly connect you amp and "always on" power from the head unit to the house batteries and use the switch config above to have the radio either power off with the ignition or stay on with the key off.

Here is a pic of the switch......switch to the right is always on; to the left the radio and amp shut off with the ignition (actually when the door is opened....my van is a 2008)



I put in a single DIN media only radio....no spinning disc. These are cheap and very cool, Android control on the radio via bluetooth, aux in, USB, and radio.
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Old 10-30-2015, 12:38 PM   #16
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Re: Stereo isolator

Mine is wired the same as Boywonder's
I've got a SPDT switch that feeds the 12+ to the head unit. The always hot 12V is fed off the the factory harness.

When I get to camp, flip the switch and the stereo is running off of the house batteries.

It's as simple as pulling the wires to where you want the switch. Mine is in my overhead console with the battery isolator switch so that I can combine banks if needed..
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Old 06-06-2020, 10:42 PM   #17
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Bringing this thread back from the dead as I'm attempting a homebrew solution similar to whats described above. I have a few questions, if someone could clarify for me it'd be much appreciated.

-I'm running an external amplifer for front component speakers and a subwoofer that I do NOT want on when running the radio from the house battery. My plan is to tap into the factory ignition switched power lead for the amp turn on as opposed to using the remote lead off my aftermarket headunit.

-I installed speakers in the three factory barn door locations that'll be power direct from the headunit in either scenario

-For switching the power sources, I am putting a 30a relay in the dash and running the factory constant power wire through the 30 and 87A (NC) terminals, and bringing a circuit from my house panel to the the 87 (NO) terminal in additon to a trigger wire from a switch in the rear of the van I'll use to switch power sources at the relay.

First question is, does switching the constant power affect the radio memory settings? I read a relay switching time is between 5 and 20ms, think there's enough capacitor reserve built into an aftermarket headunit to cover this gap of no power?

Second question, now that I've switched my constant power source I need to send current to the switched input of the radio. Can I just run a jump wire from my switch trigger lead in parallel with the factory switched wire? Would back feeding voltage into the factory switched circuit cause an issue? Would it be safe just to put a diode inline?

Thanks in advance.
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Old 06-07-2020, 08:55 AM   #18
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Here's a diagram I whipped up to better convey what I'm describing. From everything I've found online, it seems car stereos (especially aftermarket) use the constant wire for the main source of power for the unit. While the switched ignition wire is just a low current feed to wake the stereo up. Toggling the source for the switched power will indeed turn the radio on, but most of the current will still be drawn from the start battery.

I've also read that it isn't wise to use a different power sources for the constant and switched leads. It seems it may potentially cause issues with internal circuitry. I don't know how much validity there is to that statement, but I don't want to blow up my stereo testing the theory.
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Old 06-07-2020, 05:25 PM   #19
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So I got all my stereo gear installed and wired today and discovered turning the amplifier on with the igniton source creates an undesirable sqeal through the speakers till the head unit powers up. Come to discover there is a turn on delay built into the amp turn on lead in the stereo. I've updated my drawing to add a 2nd relay that will leave the remote amp lead connected until the radio power switch is toggled, much like how I'm planning on connecting the constant power. Except for the turn on lead there will be no 2nd power source.
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Old 03-14-2022, 07:57 PM   #20
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Hi Boy wonder wanted to thank you for this info and ask if there is any way you could send me a simple diagram i get the gist but want to be sure. I want the same set up yours.
Thanks in advance.
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