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78 wiring schematic

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Old 07-13-2018, 09:16 PM
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Rebuck33
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Default 78 wiring schematic

anyone know where I can get a hold of a wiring diagram for a 1978 pace car? I知 putting an aftermarket radio in and want to disturb as little as possible. I will need power to the radio and the power antenna lead identified. The old speaker wires and harnesses I知 gonna just leave as is Incase I want to ever put the factory stuff back in.
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Old 07-13-2018, 09:49 PM
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gdm78vette
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See this post
wiring diagrams
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Old 07-14-2018, 06:31 AM
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hunt4cleanair
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Originally Posted by Rebuck33 View Post
anyone know where I can get a hold of a wiring diagram for a 1978 pace car? I知 putting an aftermarket radio in and want to disturb as little as possible. I will need power to the radio and the power antenna lead identified. The old speaker wires and harnesses I知 gonna just leave as is Incase I want to ever put the factory stuff back in.
You have a couple options, maybe three in addition to the electronic version offered by the poster above. Frankly, I don't care for electronic versions and find their use limited. I like a schematic in front of me that I can lay out on the fender, and vendors now offer them in color which makes their utility much more user friendly.
So both Olsen Engineering and dr Rebuild offer a 1978 schematic with color coding. I think the Dr Rebuild uses images of components as well. He did not have his ready and I got an Olsen schematic that is large and laminated...I love it.

Another option is that in 1978, GM printed A 14 X 11 schematic that shows a circuit functionality, component location along with the wiring schematic. This is the ticket for a 78 owner and antenna is a good example. The radio is in the dash while the antenna (power) relay is under the driver's console and the antenna body is tucked up under the driver's side rear fender. One of the members here posted pages he scanned from this schematic...do a search and you may find it. The cover has a Pace Car on it. I'll use it interchangeably with the Olsen depending on what I'm tracking down.

Hope this helps!
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Old 07-14-2018, 08:53 AM
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Duke94
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I've found these vary useful. Having full color makes it easier.

https://www.classiccarwiring.com/197...iring-diagram/
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Old 07-15-2018, 05:24 AM
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Stephen Irons
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Originally Posted by Rebuck33 View Post
anyone know where I can get a hold of a wiring diagram for a 1978 pace car? I知 putting an aftermarket radio in and want to disturb as little as possible. I will need power to the radio and the power antenna lead identified. The old speaker wires and harnesses I知 gonna just leave as is Incase I want to ever put the factory stuff back in.
I'd get hold of a copy of the (period) GM publication "1978 Corvette Electrical Touble-shooting Manual". There are always a few on Ebay and it has proved invaluable to me. Large format (not often obvious in the Ebay ads!) and very clear diagrams. I used it to do just as you are ding, replace an older aftermarket radio with a newer one, and return the fade/balance controls to correct functionality.
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Old 07-15-2018, 03:41 PM
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SwampeastMike
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Wiring for the radio is easy:

Presuming a factory stereo radio with four speakers is installed, there are three connectors at the radio each of which has four wires.

Connector 1: tan (L front +), grey (L front -), light green (R front +), dark green (R front -)

Connector 2: yellow (L rear +), brown (L rear -), dark blue (R rear +), light blue (R rear -)

Connector 3: yellow #1 (+12V hot with ignition "on"), grey (dimming instrument lamps--likely not needed for replacement radio), yellow #2 (power antenna lead +12V when radio is "on"), black -12V

Use a voltmeter or test light to distinguish the two yellow wires in the "power" connector. With radio disconnected find which one goes hot with the ignition at "RUN" or "ACCESSORY". That is the lead the powers the radio.

Be aware that the stock radio fuse is only 10A and that the +12V and -12V "power" wiring are only 20 gauge. You can probably use a new radio that draws 15A or so max, but don't go any higher or you risk overheating the wiring!

Every modern radio/head unit I've seen also requires constant +12V power for memory (like station presets, etc.) You can safely tap in to any orange wire you find in that area as in our cars orange always indicates fused, constant +12V. The current draw for the radio memory is inconsequential. The best type of splice to use for such is called a "Western Union Pigtail". To make this splice carefully split and remove a small section of insulation on the wire to be tapped. DO NOT CUT THE CONDUCTING WIRES! Strip off a decent amount from one end of the new (pigtail) lead. Tightly wrap the pigtail around the stripped main wire section. SOLDER! Tape nicely. This makes an extremely secure connection that doesn't change the cause problems when the main wire is part of a harness and in the very unlikely even that it's stressed and comes loose the main is likely to stay intact. Whatever you do, NEVER use twist-on wire nuts in a car as the constant vibration WILL loosen them.
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Old 07-15-2018, 08:59 PM
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Originally Posted by SwampeastMike View Post

Every modern radio/head unit I've seen also requires constant +12V power for memory (like station presets, etc.) You can safely tap in to any orange wire you find in that area as in our cars orange always indicates fused, constant +12V. The current draw for the radio memory is inconsequential. T
The "modern" radios use the +12 constant not just for memory but to POWER the radio. The red (ignition)wire is just a trigger wire and does nothing but turn on the radio.

This was done for two reasons-

1) To help keep noise out of the audio- as the battery - constant +12V is usually cleaner- and if noise is present in the system -a simple solution most of the time is run a wire directly to the battery. This helps eliminate the noise as the battery acts as a filter. Using the ignition as a power source- isolating it is a lot more involved. Also a winner for the manufacturer - as only one noise filter is required- where as previously (15-20 years) two were needed. As in the C3, the wiper is on the same circuit as the radio (yellow wire) and noise could easily be introduced into the power line.

2) In most installations- the constant source is usually a more "robust" circuit- or a higher current- larger gauge wire used -as in the cigarette lighter/courtesy lights as on the C3.

I'd run a 14Gu wire to the battery-fuse it a couple inches from the terminal. 3M Scotchloc the yellow wire to the radio's ignition connection (red) and the power antenna out of the radio (blue) to the yellow wire for the antenna. (see pic center armrest 78-80 or jack compartment 81-82 ) Then just run new wires to the speakers- and no cutting is involved.


Here's wiring diagram for the 78- in PDF

http://www.keystonestatecorvetteclub...tte%201978.pdf



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Old 07-16-2018, 10:38 AM
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Rebuck33
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I can't for the life of me find in these schematics where the connects for the radio is.
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Old 07-16-2018, 11:07 PM
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Willcox Corvette
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Don't use the PDF diagrams from the Chiltons.. use this one below. First click on the picture below to enlarge. then right click on the picture below and the select copy.... open your paint program that comes with all pc's and paste it in there and save it to your desktop.... you'll have the factory schematic that you can save and once you do this then you can trace out a circuit and save it as a separate file...

Willcox


Last edited by Willcox Corvette; 07-16-2018 at 11:08 PM.
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