understanding gmc control head

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yeldarb32

Member - Posts: 2

Joined: March 13, 2009

Location: Nova Scotia, Canada

Posted: March 13, 2009 at 11:17 AM / IP Logged

I wanted to replace my plain AM with AM/FM in my '94 chevy C-1500 truck.

I got what looked like the exact fit AM/FM from a '91 at the 'junk' yard.

When I got home I discovered that the '94 AM had two rows of pins that accepted two plug at the back, as well as a coax port that accepted a standard auto type antenna coax plug.

The '91 AM/FM only had a two foot pigtail with a six pin plug at the end.

I've since come to understand that the some of these trucks have the amp/tuner under the dash and separate from the 'control head'. Why does one have an antenna connection and the other not? Am I going to be able to adapt the pigtailed wires to the newer styled harness? Or does the absence of an antenna connection suggest that I'm dealing with an entirely different animal here?

This is pretty confusing to me. Here I thought a car radio was a car radio and pretty much exchangeable.

Thanks for any explanation.

KPierson

Platinum - Posts: 3,527

This member consistently provides reliable information

Joined: April 14, 2005

Location: Ohio, United States

Posted: March 13, 2009 at 11:36 AM / IP Logged

I can only make guesses here, but I would guess the AM unit was made as cheaply as possible and they were able to fit everything in to one box.

The AM/FM unit required more space so the "brain" under the dash was added. It should, theoretically, be possible to add the "brain" and that is where the wires and antenna that connect to your AM unit would go. The 2' pigtail from the "radio" you have now would then connect to the "brain".

It's been years since I messed with on of those, but I would think that would be the solution.

Kevin Pierson

sparkie

Platinum - Posts: 2,061

Joined: November 06, 2003

Location: Canada

Posted: March 13, 2009 at 4:09 PM / IP Logged

The factory AM/FM radio is comprised of 2 parts. The control head which mounts in the dash and a receiver box which mounts under the dash. The receiver box has the necessary plugs for the power and front speaker harnesses as well as the antenna. The control head will plug into the receiver box. The box is designed to mount to the bracket just above the gas pedal and extends from the firewall to the dash below the ashtray. Be advised that GM had problems with the antennae on these trucks. If the antenna lead tip or the connector under the hood is corodded, you need to replace the antenna. The receiver box should also be inspected when you find one. If there is any rust or corrosion on the antenna jack or the opposite side of the box, the receiver box is probably junk. The antennas wouild allow water into them and corode and act as tubes to allow water to damage the reciever boxes.

sparky

yeldarb32

Member - Posts: 2

Joined: March 13, 2009

Location: Nova Scotia, Canada

Posted: March 13, 2009 at 9:56 PM / IP Logged

Thanks. I'm still a little unclear. The AM/FM is the older unit. It has a single pigtail, and I recall that I indeed had to unplug it from the box described below and behind the ashtray. I could go back and get the box from the truck and attempt to install it in my truck along with the '91 AM/FM unit that mates with it. However..

... the AM radio that came out of my '94 has quite a few more pinout connections to it's corresponding plugs, and also has its own antenna plug. If I located a '94 AM/FM would it not simply hook right up to these plugs now dangling out of my dash? Is the '94 radio a self contained unit complete with amp/tuner?

If I am able to simply hook a newer year radio up to the existing harness, do you happen to know what years would fit, or who I could call/email to find this information out? (i checked and both speakers are installed in the dash altho currently the am radio plays through the left one only).

Thanks so much.

Ween

Platinum - Posts: 1,366

Joined: August 01, 2004

Location: Illinois, United States

Posted: March 14, 2009 at 1:07 PM / IP Logged

hi,

the existing harness in your '94 has two connectors that plug into the radio. one connector is a 6 pin, the other is a 4 pin. the 6 pin connector is the power for the radio, the 4 pin for the speakers. wiring as follows at the 6 pin...orange--battery power, yellow--accessory power, black--ground, grey--illumination, dark brown--parking lights. for the 4 pin...light brown--LF spkr +, grey--LF spkr -, light green--RF spkr +, dark green--rf spkr -. as far as i know GM didn't have specific connectors for each of the radios, but you may have to extend the wiring to reach to the lower side of the tuner/amp module. the wiring locations should be stamped on the case of the tuner/amp module also. model years '88 through '94 all had the same style dashes hence the same goes for the radios.

mark

sparkie

Platinum - Posts: 2,061

Joined: November 06, 2003

Location: Canada

Posted: March 15, 2009 at 6:54 PM / IP Logged

You won't have to extend any wires, just reroute them. The harness that plugs into the AM radio is long enough to plug into the receiver box. You may have to get your hand inside the dash and pull them down as they are usually routed through a strap on top of the ashtray. They will plug into the receiver box along with the antenna. Mount the receiver box with these plugs on the top side of the box. You need a GM clip/stud to clip into the box to allow you to secure it to the bracket between the firewall and dash. The control head portion of radio will plug into the bottom of the box. There is a long square hole in the bracket that allows the plug to insert into the reciever box. The extra plugs in the receiver box are for rear speakers (top of box) and the remote cassette deck (bottom plug).

sparky

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understanding gmc control head

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