Topic: 1977 stereo wiring on a 79 speaker set up

[medicman]

Hey everyone,

I have found a stereo that will fit in my new dash. It is a 1977 stereo but with this comes a few slight problems, I know that the stereo only supports 4 ohms and my speakers in my 79 t/a are 10 ohms and that could damage the drivers in the stereo.

The plug on the stereo 1977 has the basic 5 wires, ground, +12, lamp, R-spkr, and f-spkr.

Here are my questions, 

1) Since my speakers have two wires on each one + and - what do I do with the - wire off each speaker?? Should I gound them to the body? (only thing that makes sense to me)

2) If I join both + speaker wires from the rear to each other, would this reduce the ohms enough for the    stereo to handle??

3) what do I do with the front speaker to reduce it to 4 ohms, I believe it is 10 ohms since it has two wires coming off it also.

4)If I was to buy 4 ohm resistors and tie them into each + wire of the speakers. would that work??

Cheers,

Medicman

[kc79ta]

The problem is the other way around. It's when the speakers (mostly aftermarket) are 4 ohm, and you hook them into an original factory radio that was made for 10 ohm speakers. If this is the case the fix is simple.

For the rear: (+) from the radio to the (+) of first speaker... (-) of first speaker to (+) of second.. and (-) of second to ground. I recomend all grounds (radio & speakers)  tie at one point to the chassis.

Front: You will need to get a resistor/s to get the ohms at 8 or better. Don't use a small cheapy. Use something like in the link below. I would use 2 wired together in parallel to the (+) of the front speaker, and the (-) to the same point as the other grounds.

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=004-10

Other wise running speakers with a higher ohms will not damage anything. It just won't play as loud....Well, unless of course you just kept turning up the volume to try and make it play super loud.

[ta78w72]

77 used grounded speakers, 78 and thereafter didn't.  I've never done it, but I would think the ground wire should attach to the speaker at the metal housing....but I'm not sure if there's something unique about the older speakers.  If you try connecting a 78 radio to 77 grounded speakers you'll blow the radio.  I'm not sure about the other way around.

[medicman]

Ok, I know the speaker are original from 79 and they have two wires and the stereo is from a 77. the 79 speakers are 10ohms.

So what you guys are saying is that the speakers wont hurt the stereo. right?? I guess I have to figure out how to wire a two wire speaker to a single wire stereo.

Hate to kill stereo by wiring the - to the speaker its self. I could not see why it it would not work.

Wounder how I can find out if this will work or not.

[medicman]

I found this write up on the 70-77 harness, does this make sense?? does anyone have a wiring diagram to confirm it??

http://www.firebirdtransamparts.com/techinfo/harness/optionwire/optionwire.htm#ra

thanks.

[kc79ta]

The speaker (-) just go to ground. The (+) goes to the radio. The reason I like all the grounds at one point on the chassis is this is this helps cut down on noise. You can ground them anywhere if you like. Do you have 1 or 2 rear speakers as this radio was only made for 1 rear and 1 front. If you have 2 rear you can get that to work as well. Just have to wire a little different.

Using 10 ohm speakers will not hurt anything. I thought they used 10ohms on earlier modles as well. Speakers don't care if the radio is a 1 or 2 wire setup. because the speakers them selfs still have 2 wires going to them (+) to the radio and (-) to a gound that feeds through the chassis to the radio.

Is the 77 radio a stereo or mono? I didn't think the stereo came out till 78?

[medicman]

For some reason, Firebirds and Trans Ams used 1960's style radios up to 1977. Trans Ams featured separate console-mounted tape players and single speakers long after the rest of GM had changed. The 70-77 I.P harness only needed two wires to accomodate a radio, for the power and lamp. T

The front speaker used a single green wire (no ground) with a large plug. This plug allowed the IP harness and a rear speaker (if used) to piggyback on it. The rear speaker had two wires (including a ground) which gave a total of 5 wires in this plug. As far as I know the radio was grounded only through its rear brace.

This is what I found on the net about the wiring about the 77 stereo. The part about the rear speaker having two wires confuses me, I thought the 77 did not need a ground to the rear speakers??