resto series number 5: Electrical Gremlins


Story and Photos by John L. Bellah

Perhaps your collector car doesn’t want to start on cold mornings, runs roughly, or some electrical systems refuse to function. Perhaps it may be time to replace the wiring harness, or convert the vehicle over to 12-volts. On the other hand, especially if you intend to keep the vehicle in original condition, a 12-volt conversion, complete with an alternator, may not be the way to go.

Automotive electrical #101:
Automotive electrical systems are usually either 6 volts or 12 volts, with the exception of many military vehicles which are 24-volts. Most older U.S. vehicles manufactured prior to 1956 are 6-volts. A 6-volt vehicle will have three vent caps on the battery. There are exceptions to every rule, and the exception is some imports (along with some GM and Chrysler vehicles) beginning around 1953 that were 12-volts. Volkswagen continued with 6-volt systems up to 1967. A well-maintained stock automobile that was originally 6 volts will probably function well on the stock electrical system. However, if you plan to install a lot of modern accessories, such as an 800-watt super-mega sound system, or to restify a 1952 Chevrolet Bel Air by installing a 454-cubic-inch Chevrolet engine, you should consider converting over to 12 volts as the 6-volt electrical system will not have the required energy to handle spark requirements on a high-compression engine.

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 On 12-volt vehicles, the battery will have six vent caps. A 12-volt battery installed in a 1948 Hudson is a sure sign the vehicle has been converted over.

Six volts or 12 volts, what does it all mean? Voltage is similar to water in a garden hose — it is the amount of pressure that is pushing the water out. Amperage would be the amount of current, or the size of the garden hose. Multiply the voltage times the amperage and you have wattage. A 100-watt light bulb in your house will draw less than an amp, as household electricity runs about 117 volts. A low beam head lamp on a 6-volt vehicle rated at 40 watts would require about 7 amps, while the 12-volt bulb of the same wattage would require only 3.5 amps. Thus, the 6-volt wiring is thicker to allow more current (or amperes) to handle the electrical load than the 12-volt system.

Electricity travels in a circuit and will eventually return to ground. This is why there is a wire leading to the electrical component supplying power and the return current is connected to the body or frame, to return to the battery. One of the battery terminals will be connected either to the engine block, body or frame. On most 12-volt systems the negative (-) post is grounded. However, foreign — especially British — and some earlier U.S. vehicles had the positive post (+) grounded, while others grounded the negative (-) post. Not knowing which terminal is to be grounded can be a source of headaches, so a good place to start is with the appropriate shop manual or wiring diagram for the vehicle application. If one is considering a modern 12-volt conversion on an older vehicle with positive ground, consider the fact that the stock gauges, radio and other accessories may not function properly due to the difference in polarity.

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Another polarity issue concerns the ignition system, which must have the proper polarity to operate properly. Reversed coil polarity will show up as hard starting and misfiring at high speeds and loads, because the reversed polarity is causing the spark at the spark plugs to jump in the wrong direction, requiring 40 percent more voltage to fire the plugs. Some of this problem can be traced to aftermarket components. An aftermarket “universal” (applicable to many makes and models) ignition coil may have the primary terminals marked with a plus (+) minus (-) or “Batt” and “Dist” wires. Hooking up the primary or “hot” wire to the + or “Batt”. terminal would be fine on a Chevrolet, which is negative ground, but would be wrong on a 6-cylinder “flathead” Dodge or Plymouth which is positive ground. A quick check for correct coil polarity can be made using an ignition oscilloscope. Most tune-up shops will have this diagnostic tool, and the charge to “scope-check” the engine should be nominal. An upside-down pattern indicates the coil polarity is reversed. Changing the primary ignition wires is the quick cure for this problem.

Twelve-volt ignition systems usually only operate on about 7 volts, because 12 volts will burn the ignition points out in short order. Most 12-volt vehicles either have a ballast resistor, or resistor wire, built into the wiring harness to reduce the voltage to the points. Constantly burning up points, or point contact surfaces appearing to be blue, are indicators that too much voltage is reaching the points. While 12-volt ignition systems only require 7 volts, the added draw of the starter reduces available voltage to the coil when the engine is started. Some manufacturers engineered circuitry that over-rides the ballast wire or resistor and will shunt 12 volts directly to the coil when the ignition is in the “START” position. Sometimes this is built into the ignition switch itself or is the extra terminal on the starter solenoid. Twelve-volt vehicles that are hard to start should have this circuitry checked. Anyone contemplating converting to a 12-volt system, with standard ignition, needs to keep these facts in mind. When converting over to a pointless system, it would be wise to consult with the ignition manufacturer to find out what is required.

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Aftermarket electrical components can also be a cause of headaches. When a new model vehicle is introduced, the aftermarket manufacturers will begin production of their own line of components based on the original manufacturer’s specifications. Sometimes, the specifications are revised later in production. (How many times has a parts counterperson told you that a certain component has been superseded?) The problem is that the aftermarket manufacturer may still be producing components to the original set of specifications. Another problem with aftermarket components is the proliferation of off-shore or the out-and-out counterfeiting of components, which are often of inferior quality.
Ancient wiring and dirty, corroded connectors can develop into major problems over time — especially if the vehicle has been sitting for long periods and rodents have gnawed at the insulation. Another source of problems can occur when mechanics probe electrical wiring with a pointed circuit tester through the insulation. This practice can cause unseen internal damage to the wire by breaking the stranded conductors or causing moisture to enter the insulation and causing corrosion. If a pointed probe is used, try to have it only touch the connectors and don’t poke it through the insulation.

Any replacement wiring should be of the same color as the original wiring to avoid confusion, and the conductor (wire) needs to be of the same thickness or gauge as the original wiring. One of the problems on a 6-volt system is when a replacement battery cable is installed. Some people will trot to the local auto parts store and find a cable that “fits.” While the terminal and connector appear “right,” in all probability, the replacement cable will be much thinner as it was intended for a 12-volt system. (Twelve volts are better than 6 volts, right?) This is a guarantee of problems and can be the reason why some vehicles are needlessly converted to 12 volts. A 6-volt electrical system requires twice the amount of current to do the same amount of work as a 12-volt system.

Also be cautious as some inferior wiring may have very thick insulation, but inadequate current capacity. A quick way to check is to feel the cable after cranking the engine for several seconds. If the cable is hot, it is either inadequate, or there is a bad ground connection somewhere. 12-volt battery and ground cables run from 2-6 gauge, with the larger number being the smaller conductor. A car with a low-compression engine and few electrical accessories can get by with a 6-gauge battery cable. Four-gauge is considered standard and a large car with a lot of electrical accessories will require 2-gauge cables. A correct 6-volt battery cable is either 0-gauge or 00-gauge and will run about 1/2 inch in diameter (including insulation), with 5/8-inch-thick cable preferred. If your 6-volt vehicle has battery cables that are less than 1/2 inch in diameter, those cables need to be replaced. 
The best method for attaching electrical connectors to wire is to crimp and solder. The next best is to crimp, provided a quality crimping tool is used with quality connectors which are crimped properly. Do not use connectors crimped onto an existing wire with a pair of pliers, except in an emergency. Such connectors can damage the existing wiring and are subject to internal corrosion — especially in areas with high humidity and salt, as near the ocean.

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Poor grounding is another source of electrical gremlins. Your collector vehicle may have had dozens of mechanics, or so-called mechanics, working on it during its service life. Over that time, the engine, transmission and other components may have been removed and replaced with grounding straps, which connect the engine to the frame or body.
These eventually may become frayed, ignored or discarded during re-assembly.

Another possibility is when the vehicle underwent a ground-up restoration and the body and chassis were flawlessly painted to perfection. When the vehicle was reassembled, were the grounded areas stripped of paint and the surfaces cleaned before the ground straps installed? Or were they installed at all? One should consult with a shop manual or wiring diagram to determine what is required for your collector car to ensure happy motoring.

Old wiring harnesses can become brittle and the insulation chafed, causing short-circuits. Another problem is corrosion which can develop internally, causing poor electrical contact.

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A word on batteries. Battery technology is constantly changing and batteries are considerably better than the batteries that were manufactured in the past. Today’s batteries, while far better, do not like to be “flattened,” or to be completely run down as would happen when the dome light, or other electrical item, is left on for several days. Back in our school days, when your old ’59 VW Bug wouldn’t start, a push start would get it going, provided you parked on a hill or had a sufficient number of friends to help push it (one could seemingly complete the school term this way). With today’s batteries, “flattening” a battery takes a considerable amount of life away from it. “Jump-starting” the car and charging the battery will appear to cure the problem, but the damage has already been done. “Flatten” a battery several times and it will become useless. The problem is when the owner takes the vehicle to a repair shop. The shop will recharge the battery and load-test it, but unless the battery is really on its last legs, the load test will show the battery is fine when it really isn’t. So it is important to tell the technician the history of the battery.

Another problem is in “jump-starting” a vehicle with a dead battery and then driving it several miles to recharge it. This practice is extremely hard on generators and alternators. It is best to have the battery recharged slowly, or invest a few dollars in a home charger. While newer cars have slight electrical drains from the sound system memory, or on-board computer, older cars can also have drains from the electric clock or a short in the wiring. For long-term storage it is best to invest in a battery disconnect switch, or to remove a battery cable from the terminal. Some will completely remove the battery for long-term storage and either periodically charge it or place it on a trickle-charger. Long-term storage of a partially-discharged battery will lead to sulfating, making the battery useless.

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Keeping the terminals clean will also reduce starting problems. The charging system will kick up extra voltage to overcome the resistance of dirty connectors, and excessive voltage will quickly burn out light bulbs. If bulbs are frequently burning out on your vehicle, it would be advisable to have the charging system checked.

Automotive Electrics #102:
An automotive test light is one of the most basic pieces of test equipment. It appears to be a pointed screwdriver with a length of wire sticking out of the handle, and an alligator clip on the end of the wire. The alligator clip is attached to a grounded surface and the probe is touched to a power source. If the bulb lights, that is an indication that power is getting to the component. Prices for test-lights vary from those available at discount stores to more professional models. My advice is to stay away from the cheap units as the bulb filaments easily break under hard usage and the internal connection can pull apart.
A Volt-Ohm-Meter (V.O.M.) is another useful tool; in addition to indicating the circuit is “live,” it will also tell you how much voltage is available. The V.O.M. can also measure resistance, thus pinpointing poor connectors and grounds. Digital V.O.M.s can be found in the $10-15 range, if one shops around.

Inexpensive hand-held battery load-testers can be obtained for less than $50. These devices connect to the battery and place an electrical load, which will give indications on battery condition and charging system performance under load. Specialty companies sell a wiring harness tool that will unlock the tabs which secure the connectors inside the plastic wiring harness connectors. Absent such a tool, a very thin and narrow-bladed screwdriver, such as used for eyeglasses repair, can pop back the little connector tabs.
Other miscellaneous tools include a hand-held wire brush or battery-terminal brush to clean terminals and connectors. Induction ammeters are handy as they can be placed parallel to a wire to determine current draw. A can of contact-cleaning spray, such as WD-40 should also be included. As well, a shop manual or repair manual and/or wiring diagram are useful.

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In tracking down electrical gremlins, start with the battery. Are the terminals clean and tight? Is it fully charged? How old is the battery? If it is more than three years old, it may be due for replacement. Fully charge it and load-test it to determine its health. If the case is cracked, it should be replaced. If the battery has been overcharged long enough that the electrolyte has boiled out, it should be replaced, but after the cause for overcharging has been corrected.

Be careful when working on a battery as the battery contains sulfuric acid, which will burn holes in clothing and can cause severe burns and eye damage if splashed.  While being charged, a battery will generate hydrogen gases which can explode. Wear old clothes, use eye protection, and have running water handy in case any acid is splashed. If splashed, you should seek medical attention.

Care should be used when removing and installing battery terminals on battery posts. Do not twist them off or pound them on with a hammer. This rough treatment will loosen the terminal post from the battery, and will possibly crack the case, causing acid to leak.

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Take the time to use a terminal puller to remove the cable. The same goes for re-installing the cable to the battery. Take the time to ream the terminal or expand it, rather than pounding on it with a large hammer. To clean corrosion from a battery, use baking soda and water, taking care not to allow any baking soda to enter the cells. This will neutralize the electrolyte in the cell(s), ruining the battery. Batteries don’t like excessive vibration, so make sure the battery is properly secured with a hold-down.

Check the connections going to the starter to see if they are clean and tight, and that the wiring is the proper size. Often the starter solenoid can be the culprit on an intermittent “no-start” condition. If the starter drags and the battery is in good condition, it may be time to pull the starter for replacement or to be overhauled. Many auto parts stores have the equipment to test batteries, starters and alternators and will test them for free.

Going on to the charging system, the first thing that should be checked is belt tightness. Just because the engine spins the alternator, doesn’t mean it is charging adequately. With the engine off, try to rotate the generator pulley. If the pulley slips when the pulley is rotated by hand, the belt is too loose. If the belt is glazed, it should be replaced. Consult your shop manual as to how tight to tighten the belt as over tightening will quickly ruin the bearings.

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Strange noises coming from an alternator, along with lowered output, may indicate a faulty alternator diode. On cars equipped with a D.C. generator, if the generator or voltage regulator have been disconnected from the electrical system, the voltage regulator will need to be re-polarized. Consult a shop or repair manual for the proper method.

A common cause of problems is the electrical connector from the engine compartment to the rest of the vehicle, which connects at the firewall. In many vehicles, rain water will run down the back of the hood and down the firewall. The problem becomes more acute as the vehicle ages and the weather-stripping ages and deteriorates. Water gets into the firewall connection and soon corrosion develops, causing problems. Carefully disconnect the connector to inspect the condition of the contacts. Clean off whatever corrosion has occurred on the contacts and ensure they are straight and tight. Prior to re-assembly, a spritz of contact cleaner, such as WD-40, will help prevent further problems.

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Sometimes a problem can be corrosion at a fuse connector, or the fuse itself is bad internally. If a fuse continues to burn out, do not replace a fuse with a fuse of a higher amperage rating until the reason for the failure has been determined.

Some vehicles manufactured from the 1970s and later use fusible links within the wiring harness. Some of these links are marked, and some aren’t. If there is power at the battery, but none reaches the ignition switch, suspect the fusible link has been burned out. Consult your shop manual for proper repair/replacement procedures, and determine what caused the link to burn out.

Intermittent electrical problems can be most frustrating to try to track down. They require patience and perseverance and sometimes it is necessary to reproduce the actual conditions before the problem will present itself. Be persistent!

The author, John L. Bellah, has an extensive background in automotive repair, having worked as an automotive technician/mechanic for several dealerships in the Los Angeles area. He is a member of SAE International and has written numerous articles for automotive publications. Currently, he is technical editor for a fleet publication.


While this terminal appeared to be in good condition, over a period of time, heat vibration and internal corrosion caused it to deteriorate to the point where a light pull would separate the cable from the battery terminal.
Some of the common tools used to maintain and check electrical systems.
Battery/charging system load testers are inexpensive and can usually be obtained for less than $50.
This inexpensive wiring harness tool is useful in disconnecting terminals from plastic wiring harness connectors. In a pinch, one can use a small screwdriver, such as used in repairing eyeglasses.
An induction ammeter is inexpensive and clips around one of the main battery cables. It can offer information on charging system output or starter draw.
A test light is very useful in tracking down problems and checking fuses. Use a good-quality test light as inexpensive ones can be unreliable.
Corroded battery terminals can be an indication of trouble.
Clean battery terminals using a cleaner or wire brush.

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