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db 06-22-2004 21:43:40 64.12.116.204 10559 Report to Moderator	I picked up the speaker wiring harness for my 1975 GMC that runs from the back of the radio to run 4 speakers along with the original 4 speakers. That is the kind with the big push buttons, pre digital. I have a GM digital radio from the 1980's vintage which the speaker wires I bought plug into. The problem I have is, I don't have any pin out diagrams in my manuals for the radios, so I don't know if they are plugging into the correct positions, for example, will I be plugging power wires into a speaker outlet on the radio? I don't think that would be the best idea. Also, there is an extra wire out of the back of the digital radio, what is that for? [Reply]  [No Email]
db 06-27-2004 18:46:58 64.12.116.204 10600 Report to Moderator	Re: Newer GM radio in 1975 GMC in reply to db, 06-22-2004 21:43:40   Thanks, everything helped. I just bought the accessory parts book for all 1975 GMC trucks on Ebay, it is supposed to have part numbers. I'll be able to round up all the right stuff with that book to straighten out little things that are wrong with my truck. right now, I'm building an air compressor and torch set into it's utility bed. The radio will be nice since I spend a lot of time in the truck.   [Reply]  [No Email]
Tim Shaw 06-23-2004 11:33:23 209.74.226.29 10567 Report to Moderator	Re: Newer GM radio in 1975 GMC in reply to db, 06-22-2004 21:43:40   If the digital radio has a clock then there would need to be an unswitched hot wire so the clock will keep time. That could be the extra wire. The Delco radios had 3 plugs, black plug is for power, ground, light in the dial, and power antenna (usually not used). The white is front speakers and the blue is rear speakers. Years ago you could buy a little kit from GM that contained all 3 plugs, ends for the wires, and a wiring diagram.   [Reply]  [No Email]
John ne. 06-24-2004 13:31:24 209.74.227.248 10574 Report to Moderator	Re: Re: Newer GM radio in 1975 GMC in reply to Tim Shaw, 06-23-2004 11:33:23   If the radio is from a very new vehicle, the you may run into trouble making it function, as more and more vehicles are keying the radio thru the body control computer, remove the radio once, and one needs a code to reactivate it. Some radios cannot be crossswapped between lines of cars period.   [Reply]  [No Email]
Tim Shaw 06-24-2004 20:28:39 209.74.226.32 10577 Report to Moderator	Re: Re: Re: Newer GM radio in 1975 GMC in reply to John ne., 06-24-2004 13:31:24   I believe db probably has a mid-80s shaft type electronically tuned radio since it plugs into his '75 harness. My brother has one from an '87 PU in his newly refurbished '79 Silverado and it was an easy swap. He also added the '81 - '87 factory cab corner speakers which were also available from GM in a kit if you wanted to upgrade a pickup that wasn't equiped that way from the factory.   [Reply]  [No Email]
John Van Valkenburgh 06-23-2004 04:41:27 216.187.239.226 10561 Report to Moderator	Re: Newer GM radio in 1975 GMC in reply to db, 06-22-2004 21:43:40   Try this site: http://www.installdr.com/QuickWiring.html Click on GM/Saturn and it will open an Adobe Acrobat file that shows various pinouts. I'm guessing the extra wire on the Digital radio is power for the Electric Antenna. Usually provides power when the radio is turned on. Good luck, John   [Reply]  [No Email]