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Electrical - Interior

By Jeff Zurschmeide

Of all your wiring issues, getting your interior working properly can give you a pain in the neck -literally. Legendary contortions are often required to get under the dash and wire up all your gauges, switches, and lights from the backside. Yet this is one place where completely disassembling your car for restoration is a distinct advantage. If everything’s apart, you can do a lot of that wiring work with the dash out of the car, or at least partially removed.

No matter what, you’re going to want to handle this wiring with the seats, interior panels, and carpet out of the car. You are almost certain to have to route some wires behind and under those parts. Overhead dome lights don’t just glow by themselves! Plus, for the work that you really must do under the dashboard, it’s more comfortable to have room for your body to stretch out.

There are a couple of handy tools you’ll want to have. The first is a headlight - not the kind up at the front of the car, but a flashlight attached to a pair of safety glasses or a headband. Getting a good look at your working area when you’re under the dash is next to impossible, and sitting there with a hot droplight next to your cheek is even worse. You need a light that illuminates where you’re looking and doesn’t require one of your hands to hold.

Take your time under the dash and make sure each wire is solidly connected to its assigned post. Pay special attention to your grounding points, especially when there are multiple ground wires attached at a single point.

HINT Hint...
You can use twist-ties to hold wires in place if they have a tendency to flop down. A twist-tie is reusable and easy to install and remove.

By far the most critical restoration points for your interior are your gauges. These instruments are delicate and must be restored by a specialist. Frequently, gauges such as speedometers and tachometers use magnets that may need to be freshened, and other gauges may include pressure switches and sealed tubes. Send all your gauges to a reliable restorer. Your marque club and national owner’s club should know who specializes in your car’s particular gauges.

HINT Hint...
If you’re having a temperature gauge (for water or oil) restored, be sure to also include the temperature sender. The gauge restorer can calibrate your gauge to your particular sending unit for accurate readings.

When you’re having your speedometer restored, be sure to note the original mileage (if that reading is accurate) and then decide if you want the odometer to be zeroed or kept at the original mileage. Note that depending on the age of your car, it may be illegal to roll back the odometer for any reason.

Finally, if you’re converting your older 6-volt car to 12-volt operation, note that virtually all of your gauges will need at least a little work. 12-volt bulbs are generally larger than 6-volt, and any internal gauge electronics will need to be examined. Even simple gauges such as fuel level rely on electronics for accurate readings.

Dos and Don'ts
Thumb up  DO
  • Change all the light bulbs in your gauges - It’s easier when they’re out of the dash
  • Have your senders and gauges restored together
  • Have your speedometer calibrated and refreshed
  • Wire up your dashboard carefully

Thumb down  DON’T
  • Don’t expect 6-volt gauges to work with a 12-volt system
  • Don’t let your underdash wiring become a mess
  • Don’t reuse abraded or cracked wiring under your dash
The Popular Restorations Feature Car
Author photo

1946 Packard: Interior electrical system



The Popular Restorations feature car has a fairly basic interior electrical system. It has the usual switches for exterior lighting, turn signals, windshield wipers, instrument lighting and a clock. This Packard was originally ordered with no radio so there is a fair amount of empty space under the dash. Where it differs from most cars is that it has four heaters, six courtesy lights, and three cigarette lighters.

Back of dashboard - while still out of the car

The majority of the in-cabin wiring is handled by the “main” harness. The “body” harness is a long loom of wires that goes from under the dash, up into the ceiling above the driver’s door, and then all the way to the back of the trunk. The power for the rear courtesy lights, heaters, and cigarette lighters runs in the ceiling on the other side of the car.

When I purchased the car the gas gauge did not work properly. It read accurately until it got down to about three-fourths of a tank and then the needle would drop to empty. I took the sending unit to Abbott Instrument Restoration and had it rebuilt. Later on, after the car was running, the oil pressure gauge needle got stuck to one side so I had it rebuilt too. Now all the gauges work perfectly.

In a couple of cases the harnesses from Rhode Island Wiring did not include wiring components such as the wires that solder on the windshield wiper motor or the wires that go into the turn signal switch. The existing wires were in reasonably good shape so I put clear shrink tubing over them to ensure they were insulated properly and to keep them from breaking apart later on.

None of the switches needed to be replaced and all of the heater motors work well, so all in all the interior electrical restoration went very well.



Abbott Instrument Restoration

By Jeff Zurschmeide

Bruce Abbott, Owner
10860 SW 74th Avenue
Portland, OR
(503) 246-1287

PR: Most people, including restorers, have no idea what happens inside gauges. Can you walk us through some of that?

BA: There’s a lot to it. There are many totally dissimilar types of engineering to give you a gauge. There are a lot of different manufacturers, particularly early on in the 1920s. The gauge industry mirrored the auto industry before the depression. You had all these different automakers and they were all striving for their niche in the market. Same thing with the instrument manufacturers -there were tons of them. Early on, cars really had no gauges, or just two gauges and that was it. There was no established standard for how to make those gauges -they could be anything anyone thought up. So if you get back to early gauges, you get some really goofy designs, and maybe they were only around for a year or two, until people figured out that they didn’t work.

PR: Take us through your restoration process?

BA: In the initial process, I like to find out what the customer wants. I assume they want the gauges to be functional, but sometimes people don’t care about the clock, for example. They just want it to look nice and stick it in the dash. But the fuel gauge, the speedometer, the temperature gauge or oil pressure, in order to have a functional car you need those things to work. So we go in with the assumption that you want the instruments to work. Then there’s the cosmetic aspect -how perfect do you want the gauges to look? You tell me if you think they look pretty good or if you want them to be perfect.

PR: How do you approach cosmetic issues?

BA: I can usually look at the faces and tell you whether or not we can go in there and clean them up. There are a number of techniques we use to brighten them up and freshen them up. Most people are quite pleasantly surprised at how good we can make an original gauge face look. They thought they were going to go through the expense of having the faces refinished. If we can brighten up the originals, that’s quite a bit of savings for them. But it’s all up to the customer. If someone says they’re taking their car to Pebble Beach, they’ve just answered all my questions.

PR: Can an amateur doing a restoration expect to work on instruments themselves?

BA: Frankly, no. They don’t have the equipment or the expertise and it’s just beyond them.

PR: What advice would you give to an amateur restorer - should they pull all the gauges and the gauge sending units and send them together?

BA: You can have fuel senders, oil pressure senders, and temperature senders all with separate electrical gauges. With old cars, many of the sending units have been switched, and the car owner doesn’t know it. Both ends of the gauge have to be correct for it to work. A lot depends on what we’re doing. If we have 6-volt gauges and they’re going back into a 6-volt application, that’s one thing. But if it’s a custom application such as a 12-volt conversion, we may need a higher temperature gauge range, higher oil pressure range, and all of that.

Click on any item below for more details at Amazon.com

Peter Wallage, John Wallage
Repairing and Restoring Classic Car Components
Haynes Publishing, Hardcover, 2002-01-17
This book will show you basic workshop techniques, such as welding, grinding, riveting and soldering. It walks you through specific restoration tasks such as restoring door locks, fuel pumps, distributors, speedometers, and much more. It has a full chapter on windshield wipers and their motors. The focus is on British cars.

Jim Horner
Automotive Electrical Handbook
HP Trade, Paperback, 1987-01-01
This is the fundamental book on automotive wiring and electrical systems. All the bases are covered here for restoration or custom work. If you need to completely rewire a car, this is the book to have.

David N. Wenner
Petersen's Basic Ignition and Electrical Systems
Green Hill Pub, Paperback, 1977-11

This is the classic work for understanding older automotive electrical systems and components. With chapters on ignition and generators and starters, it’s all covered in detail in this book. Plus, this book was written long enough ago that things like points and DC generators are covered in detail - down to the level of brush replacement and reassembly.

Haynes' Automotive Electrical Manual
Thomson Delmar Learning, Paperback, 1999-01-15
A complete guide to electrical system troubleshooting, repair, maintenance and rewiring. Clear step-by-step instructions and hundreds of photos show you how to do a professional job yourself.

Matt Strong
Custom Auto Wiring & Electrical HP1545: OEM Electrical Systems, Premade & Custom Wiring Kits, & Car Audio Installationsfor Street Rods, Muscle Cars, Race Cars, Trucks & Restorations
HP Trade, Paperback, 2009-04-07
This book covers electrical theory, wiring techniques and equipment, custom wiring harnesses for racing, hot rods and restorations, pre-made wiring harnesses, special electrical systems (navigational, audio, video), troubleshooting common electrical problems, dashboards and instrument, and trailer wiring.
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We have used Abbott Instrument Restorations (featured above) and can recommend them. Here are some other businesses that do instrument restoration:

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