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Radio install electrical issue
Hi all! I'm looking to access the collective electrical wisdom of the forum with my radio install. I will share the full story once completed.

My current roadblock is that the radio only works on ACC from the car battery and I and the good folks at Crutchfield can’t seem to find a source of the constant “hot” from the coach batteries. I spent a couple hours with them on the phone hunting down where I might be able to tap in to with no luck.

I’ll start from where I think things may have gone wrong then update as we move forward.

I disconnected the negative from the chassis batter per Crutchfield instructions. I then pulled out the radio and cut the wires on the harness as I had to connect them to the new harness. One of the wires sparked as I cut it (I’ll get back to this in a minute) and then I proceeded to attach all the wires to the new radio.

I then found out that the radio has two sources of power, one is temporary and turns on when you turn the key to ACC. The other is a constant 12v “hot” connection.

We connected all the lines and…nothing. To troubleshoot, we found that the radio works when ACC is on, so we isolated the issue to the constant "hot". I also checked the house fuses and the #3 and 22 chassis fuses to see if I had blown anything when I cut the wires (above). All fuses look fine.

I need help finding the constant among all the wires that are running behind the instrument panel. Complicating things are the wiring for the hydraulic levelers which might also be tapping in to power. The wire that seems to be the constant is also wired to the electric step (which is working), but it doesn’t give a consistent reading on the multimeter - it jumps all over the place from 0 to 180 etc. (Crazy, right?)

I called the radio repair guy who said I "just" need to go back to the ignition and find the 12v constant around there. I said that I wanted to be able to run the radio off the coach batteries so I wouldn’t drain the chassis battery. Using the 12v constant from the chassis would not allow for this. When I called the RV repair folk, they told me they will not touch the chassis, only the coach & suggested a radio repair person.

I have 2 concerns at this point:
1. Finding 12v constant from the rv battery
2. Understanding why I don’t get consistent 12v readings on the multimeter (is this part of the problem?)

If I can figure this out, I’m confident that I can finish the install which includes a back up camera mounted on the license plate (a temporary solution) and one last connection to the parking brake (needed to allow for video on the receiver to work - in the unlikely event we’d want to watch something on that 7” screen).

I've attached a couple of photos just for reference.

Thanks in advance!
Ray
2003 MB
Formerly 1997 TK
Re: Radio install electrical issue
Reply #1 –
"the radio has two sources of power, one is temporary and turns on when you turn the key to ACC. The other is a constant 12v 'hot' connection."

Right. In a typical car radio installation, the constant 12 V connection is a "keep-alive" for the radio's clock and settings memory, while the ignition-controlled one is what powers it up when you turn the key to ACC or start the engine. For your RV installation, I believe you want to tie those two together and power both from the house batteries.

"the good folks at Crutchfield can’t seem to find a source of the constant 'hot' from the coach batteries."

One place under the hood where you can find an always-live connection to the house batteries is the isolator. It's been a few years since I owned a Lazy Daze, so I can't tell you which terminal is which, but I'm sure somebody here can. You should be able to run a line from that terminal back through the firewall to the radio and accomplish your goal.
Andy Baird
2021 Ford Ranger towing 2019 Airstream 19CB
Previously: 1985 LD Twin/King "Gertie"; 2003 LD Midbath "Skylark"
Re: Radio install electrical issue
Reply #2 –
Hi Ray;  I'm pretty sure that you have a diode isolator to separate the chassis battery from the house batteries.  That wire from the engine alternator goes to each battery(s) through a diode. (two diodes, one for each battery). At the terminal that goes to the house battery are two yellow wires going to the two fuses (also a yellow case). One that goes to the CB radio, and one that goes to the car radio.  That one fuse may have blown. This is located on the driver side under the hood, near the diode isolator. A bit under the fender next to the radiator reservoir. The #4 red wire off of the isolator goes to the house battery through a (in my '99 TK) 100 Amp circuit breaker located in the battery box, way in the back at the top center.  It has a little black button that pops out. Press to reset, but it likely is ok.  I think the car radio fuse was 10 Amps, in the yellow holder.   RonB
RonB (Bostick) living in San Diego
Original owner of "Bluebelle" a '99 TKB
Re: Radio install electrical issue
Reply #3 –
Thanks Andy & Ron, I'll take a look this weekend and hope that another few hours of work will result in a done deal. I'll post results.
2003 MB
Formerly 1997 TK
Re: Radio install electrical issue
Reply #4 –
Can a 12V “cigarette lighter” outlet be tapped for constant 12V power? I think most LD’s have at least one in the dash.
Greg & Victoria
2017 Mid-Bath  “Nocona” towing a manual 2015 Forester
Previously a 1985 TK
SKP #61264
Re: Radio install electrical issue
Reply #5 –
Quote from: HiLola  - 
Can a 12V “cigarette lighter” outlet be tapped for constant 12V power? I think most LD’s have at least one in the dash.

Except those 12V outlets in the dash are connected to the chassis, not the house, as per the companion:

     “ The 12-volt plugs cab dash are powered by the cab battery located under the hood.”
Dave

2017 TK
Re: Radio install electrical issue
Reply #6 –
Turned out to be a pretty obvious fix. The blown fuse was in the chassis (thanks Ron & Andy for pointing me in that direction). That was an easy fix and I was able to route the remaining wires to set up the license plate frame-mounted back-up camera. Full report to follow whenever I finish the job.
2003 MB
Formerly 1997 TK