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1972 Corvette Scarlett Project Car - Dash Wiring Harness Installation

Custom wiring for a 1972 Corvette Stingray

Jeremy D. Clough Mar 9, 2015
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In our last installment on Scarlett, our ’72 coupe project car, we routed all the engine wiring through a single circular connector on the firewall in preparation for integrating the LS3 wiring and computer into our new factory harness. The alert reader will notice that although we’ve installed the front and rear lighting harnesses provided by Zip Corvette, as well as assembled the major dash components (such as the gauges in their housings), we haven’t done the dash harness yet. While the other factory harnesses were largely a plug-and-play affair, since we’ve gone non-factory with the radio, tach, and many of the smaller gauges, there’s a lot more to do than just plug connectors together. You have to actually modify the factory harness.

If you don’t plan the wiring—really, the whole car—with serviceability in mind, you’re only doing half of the job. Any car, especially one destined for the track like Scarlett, is going to have to come apart again, so you may as well plan for it. In our case, this came into sharp focus when we removed the dash from Tray Walden’s ’67 coupe at Street Shop, Inc., where Scarlett is being reborn. One look at all the individual wires that have to be unplugged, often blindly, and re-plugged later in the same fashion sent us back to Mark Stielow’s Pro Touring book, as well as Custom Auto Wiring & Electrical by Matt Strong, for ideas. Both books cover ways to put all your dash wiring into a single plug, so after adjourning to Waytek Wire’s website, we found the appropriate Molex connectors and terminals to complete the job.

If you just cut the wires and put a plug and socket where you cut them, you may only have one plug to deal with, but you’ve shortened the wires and given yourself less to work with. Unfortunately, you’ve got to add some length to the wires and that’s where it starts to get complicated—especially since we never, ever splice anything if we can help it.

We have a large selection of factory terminals and connectors on hand, so with many wires we could just cut off the terminal that plugged into, say, a gauge, and then re-terminate that wire into the Molex connector, and use the correct color 18-gauge wire to make a new wire to go from the other Molex connector to the wire’s original destination.

Basically, you’re swapping out the plastic connector (and the metal contacts in it) on the harness side of the Molex connector and making a new harness on gauge side. If a wire had a type of terminal we didn’t have (such as the dash bulb sockets), we didn’t cut those off at the end of the wire, instead we backtracked into the harness to get the length of wire we needed to go from the gauge to the Molex connector, and cutting that much out of the factory harness. Then, rather than splicing in a new length of wire, we used the factory wiring diagram to follow the wire we had cut short to where it terminated on the other end (often at the fuseblock/bulkhead connector) and replaced it completely, terminating it into the Molex connector.

We did both the tach/speedo and the gauges in the center console, so that each will install easily. The only wires we didn’t plug into a Molex connector were major grounds: one for the gauge console and one each for the tach and speedometer. Since these are larger 14-gauge wires, we used large 280 metri-pack connectors rather than the small Molex pins. Inadequate grounding is the most prevalent cause of electrical problems, so when in doubt, overdo it.

Stock Reproduction Harness 2/23

01. As with the forward and rear lighting harnesses, we started with a stock reproduction dash harness that was made by Lectric Limited and supplied by Zip Corvette. Anytime you’re this deep into a car this old, there’s no sense in repairing the original harness: they had a limited service life when they were made back during the Nixon administration.

1972 Corvette Dash Guage Custom Wiring Fuseblock 3/23

02. Along with the harness, you’ll need the wiring diagram, and, as we did with engine wiring, we used a separate spiral notebook to keep track of every change made to the factory harness. The bulkhead connector that goes through the firewall is on the back of the fuseblock. It connects to the front lighting and engine harnesses under the hood, and uses Packard 56 terminals to make the electrical connections.

1972 Corvette Dash Guage Custom Wiring Mounting Screw 4/23

03. One of the original pieces you’ll want to hang on to, assuming you don’t replace them as well, is the long, hex-headed screws that hold the fuseblock to the firewall. It’s one of the few things we’ve actually reused from the factory electrical system.

1972 Corvette Dash Guage Custom Wiring Hanging 5/23

04. While not fully mocked up, we started by hanging the dash wiring harness to get a sense for where everything is located and to make sure the plugs connected to all the right things.

1972 Corvette Dash Guage Custom Wiring Gauge Lights 6/23

05. The back of the original speedometer housing, with the bulb sockets that plug into it. Note the holes that are marked with the color of the matching wire, another good reason to keep your colors straight when rewiring things. While it’s easy to plug them all in now, imagine trying to do it in a confined space where you may not be able to see them.

1972 Corvette Dash Guage Custom Wiring Center Gauge Console 7/23

06. Here’s the group of wires that plug into the back of the center gauge console. Some of these are unnecessary, such as the ones that plug into the ammeter, which we replaced with a voltmeter. Other will need to be added, such as a signal input for the now-electric oil pressure gauge that replaced the factory mechanical one. Note the LEDs in place of bulbs—more on that later.

Custom Wiring 8/23

07. All the white-light bulbs in the dash harness (including those for the gauges and radio dial) are powered by grey wires, which all connect to one another. Our Antique Automobile Radio requires an input to turn on the dial light, so we checked its wiring schematic and then removed the factory grey wire for the dial light from its factory connector and reterminated it in the Molex connector that came on our radio. We did the same for radio power and ground.

Wiring Harness Bulb Sockets 9/23

08. Opening up the harness is one thing, but this is officially the point of no return. Since we didn’t have the bulb sockets on hand to create our own harness, we couldn’t just clip them off and discard them and then rebuild that part of the harness. Instead, we did the opposite, cutting them off with enough of a pigtail to terminate them into the gauge-side Molex connector, and then replacing the original wires on the harness side of things.

1972 Corvette Dash Guage Replace Wires 10/23

09. It only hurts the first time. Since we chose to replace wires that we cut off short with a new one (instead of running the risks of splicing the wires together), that required removing the harness tape and removing the wire from the harness all the way where it’s terminated. Similarly, wires that we didn’t need any more were removed all the way to the firewall. Note the harness tape isn’t traditional electric tape: it sticks only to itself, not the wires, and that’s what you’ll need when you rewrap the harness later.

1972 Corvette Dash Guage Custom Wiring Connector Assembly 11/23

10. Most of the electrical connections in Corvettes of Scarlett’s vintage (such as this female one) are Packard 56 terminals, which generally plug, singularly or in groups, into plastic connectors such as the single shown here. Fortunately, both the metal terminals and plastic connectors are readily available. We ordered ours from Waytek Wire.

1972 Corvette Dash Guage Custom Wiring Connector Assembly 1 12/23

11. Like most other terminals, the first crimp is to the wire, which we made using a set of Packard crimpers, and it should roll the metal of the connector around the wire from either side. The second crimp is on the insulation. While a female terminal is shown, the male is crimped the same way.

1972 Corvette Dash Guage Custom Wiring Shrinkwrap 13/23

12. While not absolutely necessary—they didn’t come that way, and we didn’t redo all of them—if we were building a harness, we generally used adhesive heat shrink to seal the connection. More than just weatherproofing it, heat shrinking both strengthens the connection and helps protect the quality of the connection between the wire and the terminal from degrading over time.

013 1972 Corvette Dash Guage Custom Wiring 14/23

13. The terminal plugs into the connector from the rear, and is held in place with a small metal tang. To remove it, insert a metri-pack tool (or a small, flat jeweler’s screwdriver) into the front of the connector to depress the tang, then pull the terminal out from the rear. Male Packard 56 terminals install the same way, but remove differently: the tab must either be compressed from the sides or cut to be removed.

1972 Corvette Dash Guage Custom Wiring Factory Connectors 15/23

14. After terminating the correctly-colored wires with new factory connectors, we simply plugged them into whatever gauge they went to, and left enough extra wire to route the wires together and get them to our Molex connector. Note that on the male connector, which is held in place with a nut, the upward-bent dogleg can easily get bent or broken so make sure to check the integrity of the terminal before plugging it together.

1972 Corvette Dash Guage Custom Wiring Back Of Gauge Panel 16/23

15. As we built each new wire, we plugged them into their appropriate hole (or terminal), and then routed them towards where we wanted the connector to be. Although we’ll put loom on them later, we used small zip ties as we went to keep them bundled together for neatness sake.

Molex Connectors 17/23

16. Molex connectors come in several different sizes. We used the 20-pin for the gauge console and a smaller 16-pin for the speedo/tach assembly. The radio came with one already installed, instead of the factory-style plug, and we’ll use another when we install the switchplate that will control most of our aftermarket accessories.

1972 Corvette Dash Guage Custom Wiring Terminals 18/23

17. Like most other connectors, you need both the terminals—the actual electrical contacts—and the plastic housing into which they seat. Terminals can either be ordered individually (like the female ones on the right) or on a reel, like the males ones on the left. Reel is often cheaper, and can be easier to manage when you’re working with them. These are very small terminals, and require a great deal of care when being crimped.

Gauge Console Wiring 19/23

18. Starting to pin out the connector for the gauge console. Keep good notes and match the factory wiring colors. It’s not as critical here—the wires are short enough to see exactly what they go to—but it’s the best practice and makes it easy to tell if you’ve plugged a wire into the wrong spot in the connector.

1972 Corvette Dash Guage Custom Wiring Wire Covering 20/23

19. We used split braid to protect the wiring once everything was together. Less voluminous (and to us, neater) than the common corrugated loom, it can expand or contract as needed and it’s easy to pull out individual wires when necessary. Available from many places (and under several different names) we ordered it by the roll, and in a few different sizes, from Waytek.

1972 Corvette Dash Guage Custom Wiring Cluster Slits 21/23

20. All the wires routed and secured in place. We cut small slits in the braid where the wires needed to come out, and then zip-tied it closed. The keen-eyed will note the brown connector in the middle isn’t correctly assembled. We’ll get to that before it goes in.

1972 Corvette Dash Guage Custom Wiring Finished Molex Plug 22/23

21. The finished Molex plug, shown with the separate ground wire. While we had empty bays in the Molex plug, we chose to go with a heavier connector for the 14-gauge ground wire. Faulty grounding is the number one cause for electrical problems, so when in doubt, go the extra mile—there’s no such thing as over-grounding something.

Molex Receptacle 23/23

22. The Molex receptacle on the harness side of things, along with the separate ground wire. Note the zip ties on the harness. Since we had to unwrap the harness tape from virtually the entire harness, we used the zip ties to keep all of the different groups of wires bundled together in their factory orientation. We’ll rewrap it all later.

Sources

Waytek
Chanhassen , MN 55317
800-328-2724
www.WaytekWire.com
Zip Corvette
Mechanicsville, VA 23111
800-962-9632
www.zip-corvette.com
Street Shop, Inc.
Athens, AL 35611
256-233-5809
www.streetshopinc.com

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