GMT800 Radio Reception Issues with Aftermarket Radios - Solution

I shared this information on another forum, but thought I would put it here, as this is something that I had to figure out on my own recently. To make a long story short - I recently decided to put a backup camera on my 2006 Silverado 1500 WT (work truck). Not that I need it, but its the truck my kids and family borrow, and with the long 8 foot bed, a toolbox that obstructs vision, AND a Tommy Gate lift gate adding almost another foot to the length, I always worry about someone backing into something with it. Once I got into it, I kinda was excited to replace the factory AM/FM radio, which has served as my sole sort of on-road entertainment all these years. I went with a Sony unit from Crutchfield, as I am picky about radio tuner performance, sensitivity, and such, and on paper, it was top notch. The kit from Crutchfield gave me a prewired harness, antenna adapter from the mini-barb GM uses to a more standard Motorola plug, and supposedly, everything I needed.

Once I spent several hours doing the install, which was mostly tied up in installing the backup camera under the lift gate and running the wire up front, you can imagine my surprise when I found nothing but static and noise across the AM band (yes, I actually listen to a couple of AM stations), and half the FM stations I listen to were missing! What the heck!

Well, a few weeks of research into the issue reveals something that Crutchfield and pretty much anyone else selling radios to GMT800 owners should know. Specifically, the factory radio sends 12V power up the center antenna conductor on that little mini-barb connector the factory antenna cable uses, to power an antenna amplifier in the base of the antenna out on the passenger fender! Without that 12V - no AM, and spotty FM performance!

No aftermarket radio provides that 12V power to the antenna unfortunately. Most as you probably know use a Motorola plug on the back of the unit.

So I went in search of a solution to this issue, but unfortunately, NO ONE currently sells an adapter that supplies power to the antenna that has the GM mini-barb socket on the antenna side, and a Motorola plug on the radio side. So... I had to improvise.

So to inject power, the ONLY suitable device I found was the Metra 40-EU55. This has a Motorola plug to go into the radio, and a separate blue power lead to connect to switched power (such as the blue & white wire coming from most receivers, or red switched accessory power), BUT the antenna side is a FAKRA connector, used on newer vehicles than the GMT800. So I had to find a FAKRA to Motorola plug adapter as well.

So we have, from antenna to receiver:

1. Metra 40-GM10 (mini-barb to Motorola plug) - Metra Part # 40-GM10 | Aftermarket Antenna | Metra Online (Mine came from Crutchfield)

2. Fakra Z Female to DIN Socket cable -
Amazon
(I used the one with the female Motorola plug and female Fakra).

3. Metra 40-EU55 (Fakra to Motorola plug + 12V power) -
Amazon


Here is a picture on the seat of the Silverado before I installed behind the radio. I added this between the radio and the Metra 40-GM10 that was already in there from the prior nstall.



I ended up connecting the blue wire on this to an unused red accessory wire in the pre-made wiring harness from Crutchfield, that was for a dangling connector to steering wheel mounted controls my truck doesn't have. Otherwise I would have cut the blue/white wire from the radio and spliced to it. Crutchfield had routed that to the connector for the factory harness, but it was an unused pin. I just skipped it as it was buried in the braid/wrap around the harness they made.

I hope this helps someone else who wonders why their AM radio stops working when they replace the factory unit in their GM truck or car! And I am kinda ticked I had to research this and work on it, and that Crutchfield, Metra and other folks that DEAL with car audio for a living don't know to give us a harness that supplies the 12Vdc to the antenna wire that the factory radio supplied.

To be honest, I could probably have built something with an inductor and capacitor, maybe a diode or two, but was too lazy to deal with that.

Hope this helps someone else who is having this issue. After this - all my AM and FM stations are back, and better than before.

Wow, I have replaced several factory radios in my GM vehicles with units from Crutchfield. I haven't lost my AM reception, but I have had weaker reception and couldn't figure out why. Thank you. I will be trying this out!

Wademo said:

Wow, I have replaced several factory radios in my GM vehicles with units from Crutchfield. I haven't lost my AM reception, but I have had weaker reception and couldn't figure out why. Thank you. I will be trying this out!

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I could pull in 3 or 4 strong AM stations without doing this, but not my normal talk radio station about 30 miles away, and most of the band between the 3-4 that did come in was just loud buzzing. Adding the power to the antenna made a HUGE difference on AM, and pulled in FM stations I was completely missing with the antenna unpowered.

My son likely has the same issue on his 2005 Colorado which has an aftermarket radio, but I think he only listens to Spotify from his phone when driving...

Excellent fix!

This is a new phenomenon to me. Any reason why a dedicated 12V antenna amplifier wouldn't work? https://www.amazon.com/KSaAuto-Universal-Amplifier-Reception-Connector/dp/B09CYJ3FBJ/

CPB said:

Excellent fix!

This is a new phenomenon to me. Any reason why a dedicated 12V antenna amplifier wouldn't work? https://www.amazon.com/KSaAuto-Universal-Amplifier-Reception-Connector/dp/B09CYJ3FBJ/

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Actually - that solution won't work as well, as the problem is that there is already an antenna amplifier built into the base of the GM antenna on these trucks, and if it is unpowered, you get barely any signal from the antenna itself, so your dedicated booster would not be getting any signal to boost. Without power to the factory antenna, you probably have less signal available at the dash end of the cable than if you had an old school antenna without such a booster built in.

As I researched the issue, some folks who ran into it had tried boosters like that, and they made little difference - due to the fundamental issue of the unpowered built-in antenna amp effectively attenuating/blocking signal from the antenna itself.

You really do need to send 12V up that center conductor.

This is technically what is needed, but this one is not for automotive use - an RF bias tee:


Something like that is built into the little cylinder in that Metra 40-EU55 that I linked. Power can feed to the antenna, but not back into the radio.

@jfmorris I know this is an old thread, but I recently swapped out an aftermarket radio for a different one, and noticed iffy reception on either. Then I found your post and installed the Metra adapters (wired it to the 'power antenna' in the harness for 12v). I am not noticing any improvement in reception - granted I live in a mountainous area, but other radios in my fleet don't seem to have any issues.

I'm wondering if the 12v adapter is hooked up to the wrong wire, or it's junk, or something else is going on - I'm using an old antenna pulled from a yard that is 6m mounted on an adapter to fit my 7m base (2001 Yukon). I doublechecked my grounds and they all look good so I am wondering if the antenna is shot? I see aftermarket ones proclaiming better reception via a 'tuned coil' but that kind of sounds like snake oil to me.

yukon-coRn said:

@jfmorris I know this is an old thread, but I recently swapped out an aftermarket radio for a different one, and noticed iffy reception on either. Then I found your post and installed the Metra adapters (wired it to the 'power antenna' in the harness for 12v). I am not noticing any improvement in reception - granted I live in a mountainous area, but other radios in my fleet don't seem to have any issues.

I'm wondering if the 12v adapter is hooked up to the wrong wire, or it's junk, or something else is going on - I'm using an old antenna pulled from a yard that is 6m mounted on an adapter to fit my 7m base (2001 Yukon). I doublechecked my grounds and they all look good so I am wondering if the antenna is shot? I see aftermarket ones proclaiming better reception via a 'tuned coil' but that kind of sounds like snake oil to me.

Click to expand...

Sorry to hear you are having issues. I would confirm that there is 12V on the wire to the Metra adapter when the radio is on, just to be sure. If your truck didn't have a power antenna originally, I am wondering if that wire in the harness has power to begin with. As I noted, I went with a red switched accessory power wire, that is on any time the key is in the ON or ACC position.

To be honest, I've not seen too many vehicles with a power antenna at all since the 90's, and certainly not a GM truck or SUV, so choosing that wire might be the issue.

That said, as you mention - the antenna itself, or the amplifier in the antenna base, could be messed up.

I switched the wire from the 12v adapter to the ignition wire and it didn't improve the reception. On a whim I went over to a car audio shop today to see if they had an antenna to test, and ended up talking to the owner....he assured me that my antenna didn't need 12v, so that left two possibilities - the base and/or antenna or both were shot.

He actually had a GM OEM base in stock so I bought it and then proceeded to destroy my forearms and my neighbors ears (from my cursing) getting it swapped out. Of course, at the last stage of tightening the antenna down, it sheared off the 7 to 6mm adapter so I couldn't test fully with the junkyard antenna I had.

I've got another adapter and a new antenna coming in a couple days, hopefully that all works.

Good luck! Let us know what happens.

I've replaced the antenna base and antenna and still have pretty poor reception, so I think the radio is junk. What do you expect for $49 right? Fancy screen and android car playstation etc. / whatever, but this thing kind of sounds bad and it doesn't even have an AM band. Time to send it back and start over....

Yeah I imagine a $49 radio likely does not have much shielding or awesome performance in many areas. I’ve never cheaped out on my radios when I go to the effort to do an aftermarket one. The only reason I upgraded the factory unit though was to get a backup camera and Bluetooth for hands free. Ended up with a Sony I’m fairly happy with.