Electrical Safety in Your Model A

by John McMillan

Most of the following are faults and/or safety hazards that I’ve encountered in Model A’s and other less worthy vehicles. The cures are neither expensive nor technically difficult.



Hold Down: Without a hold down, the battery can bounce around, resulting in case cracks and acid leakage or cable shifting and abrasion resulting in a possible short. Easy to correct.

Ground Strap: Attachment to frame should be to BARE METAL. We usually apply lots of paint to the frame and unless some is removed where the ground strap attaches, then a solid ground cannot be achieved. A coat of dielectric grease helps to promote good contact and slows rusting when applied to bare metal. With a poor ground, the starter will turn real slow, and draw far more current than it should. Easy to fix.

Cable Size: Modern cables that you can buy at your local auto shop are too small. Small cables cannot carry the current draw of a starter motor safely. They will overheat and the starter will turn slowly. The cable size should be No. 1. These can be special ordered at the local parts house, or buy them from a vintage Ford dealer.

Caps: Make sure the battery vent caps are not plugged. If they’re plugged, and the charge rate is high, the battery can explode from gas buildup inside the battery. Very exciting, very messy and very dangerous. Plugged caps are caused by dirt and, I suspect, by using hard water in the battery. Clean caps and distilled water are the inexpensive answer. I had one blow up in a German Model A (VW) and the clean up alone took about 8 hours.

Cable routing: The negative cable to the starter MUST be routed according to Ford’s plan. See illustrations in any of the Ford repair manuals. Other routings most likely will cause cable insulation chafing and a resulting short circuit. Even if you installed a fuse, this is not a fused cable, and a fire is very likely. I’ve seen this several times, the last time at Big Bear when a member complained of white smoke every time he stepped on the brake. The pedal pushed the battery cable against the bellhousing and shorted out. If a fire starts here, you need to disconnect the battery to stop the fire source. Very hard to get to, you might wind up watching your car burn while you try to remember if your fire insurance is paid up. This kind of fire can also happen after you’ve parked the car in your garage. Real easy to fix. Note that no safety switch or fuse installation will eliminate this hazard, the only way to cure the problem is to "do it right the first time", and it takes no more effort than to do it wrong.



Grounding: Must have a good ground for proper operation. A slow grinding starter is a hot starter and hot cables are not healthy cables. If your starter spins real slow, you may need to add a second ground strap from the starter mounting bolt or a transmission bolt to a bare spot on the frame. If you have Float a Motor mounts, I think this secondary cable is almost required.

Starter Switch: This is one of the items that must have been designed by an incompetent engineer. Check yours for bad insulation and shorting against the body of the switch, both very common faults with this switch. Another fault is that the switch can "weld" itself to the starter contact and keep on cranking even after you’ve removed your foot from the starter rod. If this happens, reach down and try to pull up on the starter rod. Sometimes this doesn’t stop the cranking, and the starter will continue running until the battery dies or the starter burns out. The only way to stop this if you’ve installed a mater cut off switch, more about this later.



28-29 Switch: The original switches are usually only a problem in that they can be a pain to adjust so that they work. The reproduction switches are for the most part a real problem. Actually, most that I’ve seen are a fire waiting to happen. The problem is in the insulation around the studs. A lot of the repops have poor quality red fiber that cracks easily. If this happens on the hot terminal, a short will occur that can set the input wire on fire. Symptom is a discharge reading on the ammeter and poor running engine because all the power is going into melting the wire. If the secondary terminal shorts out you’ll see a high discharge reading whenever you step on the brake. To check the switch, remove it, hook an ohmmeter from stud to ground and force the stud in all directions. If it shorts out on either stud, replace the switch. Check new switches as well. I’ve seen them in failure right out of the box. Sample melted wire available for inspection. This is another fault that can start a fire when your car is parked. A fuse MAY protect you, but 25 amps is still enough to start a fire. I fixed mine by taking it apart and machining new insulators out of delrin plastic.

30-31 Switch: Although not a safety issue, operation can be improved and squeak eliminated by silver brazing and reaming the operating rod hole in the switch body.



Points Stuck Open: This is the more common failure. Points won’t close, battery won’t charge, battery dies, and your generator fries because it’s trying to charge the whole universe. Not a safety issue, but very unpleasant when it happens away from home. Short term fix is to install a jumper wire across the cutout terminals so that the generator works properly. Just remember to disconnect the wire when you shut off the engine. If you’ve installed a master cut off switch you can just shut the switch off.

Points Stuck Closed: This is another problem, less common, but a real hazard. When they stick closed, the generator functions normally when the engine is running, When the engine is shut off, the battery feeds the generator, which now thinks it is a starter motor and tries to turn the engine over, resulting in a burned out generator, a melted out charging wire, a dead battery or a burned out car. This is another garage fire potential. If you see a heavy discharge on the ammeter when the engine is off, look for this problem. Disconnect the wire form the "batt" side of the cutout. A fuse helps here because it will usually blow. Best solution is to install a diode kit in the cutout.



Cap Nuts: Using plain nuts on the back of an ammeter is an invitation to a short circuit against the fuel tank. Use the plastic cap nuts that Ford designed for that use.

Meter Shorts: Check that there is no possibility of a short on the studs to the ammeter case back, especially on original meters. I had a near mint meter short out due to 70 year old insulation failure. This stuff does not last forever. The short melted the insulation from the wire that runs from the meter to the junction box. This is one part where a repop may well be better than the original.



Sockets: Check that the spring- loaded contacts inside the bulb sockets do not contact the wall of the socket. Some reproduction sockets can be pretty sloppy in this area. Contact will result in a short circuit whenever the lights are turned on, either in one or both high and low beam settings.

Connectors: These are the little troublesome connectors at the base of the headlamp buckets. Probably the best solution is to hardwire the lamps thereby bypassing those little rubber gizzies.



Grommets: If a wire is going to pass through sheet metal, always use a rubber grommet. If not, vibration will wear through the insulation and a short will result.

Frayed Wires: If the insulation is frayed, replace or tape the frayed area.

Wire Routing: If you are routing wires, use common sense. The worst example I have seen was a fuel pump wire strapped to a fuel line. The fuel line was leaky (Model A, big surprise}, the fuel dissolved the wire insulation so that the wire became bare. Use your imagination as to what could happen if a spark occurred.

Electric Fuel Pump: If you add one, don’t forget to add a regulator so that the pump pressure isn’t so high that fuel comes out of the carburetor. Old carburetor fuel valves cannot handle the pressure of an unregulated pump. Although not an electrical item, I did see what happened when fuel from an unregulated pump met a stray spark from a magneto on a 1913 Mercer.

Good Rule: Always check the ammeter when you shut off your engine. Never walk away from a Model A that registers a heavy discharge. If you can’t fix the problem, then disconnect the battery ground cable.

Hint: A light coating of dielectric grease on all electrical connections including light bulb bases will promote good electrical contact and inhibit corrosion. It is available at most electronic supply houses under various brand names and from your local auto parts house as Permatex #67V Dielectric Tune-Up Grease. If this grease is used on light bulbs, fuses, connectors etc., then removal is easy, without the usual sticking and subsequent breakage.



Fuse Holder: These are available from all Model A suppliers for a few dollars and are very easy to install. They provide a lot of protection from the bad results of electrical faults. Pulling the fuse when you park your car shuts off most everything and helps prevent theft as well.

Master Cut-Off Switch: Probably the best safety investment for an antique car. About $25 to buy. Cuts off all power past the battery. An additional benefit is that the battery will maintain a charge longer if you make a habit of always turning the power off whenever you stop the car. Everything connected to a battery will draw small amounts of current even when "off" due to resistance at the connections. If the switch is off, the battery does not discharge. I would not have an old car in my garage that did not have a power cut off switch, unless the battery was disconnected.

Fire Extinguisher: When all else fails and fate is working overtime, an extinguisher is really nice to have. Lacking one, try to smother the flames with sand or a blanket, jacket or whatever. If you can’t put out the fire, enjoy the spectacle, plan the restoration of your next vehicle, and figure out where you can put the hard luck trophy.