Metra 40-GM21 Antenna Adapter

Works with select 1987-up General Motors vehicles — factory male to female Motorola antenna connector

Item #: 12040GM21

In Stock

12 Reviews | Ask Questions

Your price: $7.99 Earn up to 8 Rewards points

Add to Cart

+ Add to wishlist + Email me alerts for this product

View all associated offers




Does it fit my car?

Select your car

Find what fits your car


Metra 40-GM21 adapter

The Metra 40-GM21 adapter lets you connect an aftermarket antenna cable to the factory radio. It has a female Motorola plug on one end and a right angled male GM antenna plug on the other. This adapter can also be used when installing a wired FM modulator with the factory radio. Please enter your vehicle information or call an Advisor at 1-888-955-6000 to find out if this adapter is compatible with your vehicle. Warranty: 60 days.

Note: Most vehicles will require additional installation parts — please identify your vehicle if you haven’t done so, then check here for a list of parts. You can also call an Advisor for more information.

Hands-on research

What's in the box?

Download owner's manual

  • 6.438" antenna adapter cable (one end terminating in a female Motorola plug and the other end terminating in a right angled male GM antenna plug).

Product Research


Compatibility: 1987 and later GM factory radio with mini connector to universal antenna adapter cable (factory radio to universal antenna)

Our Product Research Team

At Crutchfield, you'll get detailed, accurate information that's hard to find elsewhere. That's because we have our own in-house Product Research team — they open the box, verify contents, check the owner's manual, and record dimensions, features and specs. We stay on top of new products and technologies to help people make informed choices.

Metra 40-GM21 Antenna Adapter Reviews

Average Customer Review:

12 reviews
Review this product
Great Gear Giveaway

Submit a review and then enter to win a $500 rewards card


Review this product:

Thanks for taking the time to share your experiences about this product. Please be sure to focus your comments on the product itself. Read our Review Guidelines for more information.

Your email won't be visible. Please use the email address that is associated with your order.
(e.g., JohnD) Your review will be signed using the display name and location
(e.g., Charlottesville, VA)

Click on a star to rate the overall product on a scale of 1-5
1500 characters left
  Attach a YouTube Review
Crutchfield Video Review Guidelines
  • Only submit videos that you made or are authorized to use.
  • Do not submit videos that contain music, video or visuals that are copyrighted and belong to someone else.
  • Please see our Review Guidelines for more information.
500 characters left
500 characters left


Written By Anonymous, Indiana on Tuesday, January 20, 2015

Crutchfield Customer Review (What's this?)

Did not fit. The connections were backwards.

Cons: Did not fit, connections were the opposite of what my GM car required.

perfect fit

Written By jroman, rockford,il on Sunday, September 07, 2014

Crutchfield Customer Review (What's this?)

perfect fit adds satelite to factory radio using xm module

Pros: keeps factory radio adds satelite with module

Cons: none

worked like a charm

Written By joe, fredericksburg on Saturday, February 22, 2014

Crutchfield Customer Review (What's this?)

my only gripe with gm vehicles is their ant. cables.does anybody know the reason for using small cables?

Simple and easy

Written By AlcoholicProgram, Pittsburgh, PA on Sunday, September 01, 2013

Crutchfield Customer Review (What's this?)

Possibly the easiest thing to install so far. The GM Antenna adapter by Metra could not be any better. It does exactly as intended. If the low price scared you, or might even have you jump right into purchasing it, think again. The GM Adapter by Metra is the best product for its use and makes installing a new system that much easier and better.

Pros: Works perfect, simple install, very inexpensive.

Cons: Absolutely none.

Metra 40-GM21 Antenna Adapter

Written By Timi, San Mateo, CA on Saturday, August 17, 2013

Crutchfield Customer Review (What's this?)

Good product but couldn't use it because I did not specify which one I needed.

Just the ticket too

Written By Hap, MT on Thursday, July 04, 2013

Crutchfield Customer Review (What's this?)

This fits the radio and lets a regular antenna work on GM products.

Too long

Written By Ken, Saint Paul, MN on Sunday, May 19, 2013

Crutchfield Customer Review (What's this?)

Worked like a charm

Pros: Plugged in tight.

Cons: Too long. Had issues with stuffing it an all the other wires back. behind stereo.

Great Adapter

Written By C P, Tuscaloosa, Al on Monday, May 06, 2013

Crutchfield Customer Review (What's this?)

Great adapter, had no problems installing in my 2002 Chevy S-10.

Pros: Great adapter, easy installation

Cons: None

Metra 40-GM21 Antenna Adapter

Written By John W., Cuba, NY on Tuesday, March 26, 2013

Crutchfield Customer Review (What's this?)

Easily attached to my FM modulator.

Worked great

Written By TSub, Central KY on Tuesday, January 29, 2013

This worked great for taking my Suburban back to a stock radio. The adapter made it easy to put a factory style radio back in since the antennas are somehow different. Had no issues with loose connections either.

Don't Know Yet

Written By Billy M, Sumrall, Mississippi on Wednesday, January 02, 2013

Crutchfield Customer Review (What's this?)

Had to use this with an adaptor for FM modulator of iPod. Did not fit very tight on a GM radio. Still works, but it seems like if ever hit a large bump in the road it's probably going to come out. But I may be wrong.

Pros: Works, so far.

Cons: Fits loosely in GM radio.

Metra 40-GM21 Antenna Adapter

Written By Michael, Flagstaff AZ on Saturday, February 21, 2009

Crutchfield Customer Review (What's this?)

Why does GM use a weird miniturized Motorola antenna connector? Dunno, but they do. This is the answer (or if you are installing an XM modulator in-line, it is half the answer.)

Questions & Answers Ask the community. Share your knowledge.

Searches related to the Metra 40-GM21 Antenna Adapter Works with select 1987-up General Motors vehicles — factory male to female Motorola antenna connector