Electrical Stuff

We plan to add to this page often; if you have a question about the operation of a car, or about an import marque in general, submit it using our contact form. If it looks like it would be of interest to others, we’ll discuss it here. 

In general, chassis wiring is as likely to go bad (if not more so) as electrical components, so be suspicious — be really, really suspicious — of wires and connections before you start replacing expensive parts.

Some cars are worse than others; many of the European carmakers don’t understand insulation, especially Volvo; and my cousin’s Mustang II literally had the insulation dry up and fall off of some of his wiring, leaving the copper wire showing through.

Look particularly at connections that appear not to be original. “Scotchlock” connectors are fast and easy, but they don’t hold up forever. I’ve had to rewire things (like foglights) that were added on with Scotchlocks. Crimp-on connectors can be a problem as well, as it’s not easy to get a good solid crimp and then the wires pull out easily.

Tip from my friend (and former technician) David Doiron: “When doing electrical connections, use ‘electrical contact compound’ if you can find it. (try Eastwood). A poor cousin is Vaseline. Not as good, but MUCH better than a dry connection. Never use ‘grease’, though.”

I recall one poor customer who complained that something I had sold him didn’t fit what it was supposed to plug onto. Come to find out, there was the remnants of an old corroded connector still stuck onto the terminal he was trying to connect to…

Most ignition circuits from the early 1970s & up have two feeds for the distributor — one from the switch to the coil through a “ballast resistor” that drops the circuit voltage down to a level that won’t fry the points (if any), and a second one from the starter circuit that bypasses the ballast resistor while cranking, giving the system a little more power for those few seconds.

If you have a car that starts when it is cranked, and then immediately dies, you may have a ballast problem. We occasionally see distributors that eat points for lunch, sometimes in a matter of a few blocks. That is usually a short through the ballast, which feeds a full 12v to the points, which will often burn out on the higher voltage for more than a few seconds.

A bad condenser will also burn points; the purpose of the condenser is to drink up the electrical backlash between the coil and the points, allowing the coil to build up for its next spit, and control arcing on the points.

We once replaced a bad starter solenoid on an MGB that had had an alarm system installed and then removed, and then the car wouldn’t run! Come to find out that the main feed for the ignition had been disconnected, and the car had been running on a short through the solenoid into the ballast bypass line. When we put on a solenoid with no short, there was no power to the coil at all.

The heart of a car’s electrical system is the BATTERY. Batteries are meant to be recharged regularly, and they don’t do well sitting for long periods of time. On boats and other vehicles that are only used seasonally, it is recommended that the battery spend its off season connected to a trickle charger so that it doesn’t run down and destroy its plates. The charge will dissipate slowly even without a drain, but of course even a small drain makes it much worse. In general, a long slow trickle charge is more effective than a quick recharge.

One fairly common cause of battery problems on 1970s vintage MGs is the anti-run-on solenoid, which turns on when the car is turned off and is grounded through a reversed oil pressure switch. (Note: if you ever run onto an oil pressure switch that looks exactly like the common one but is painted red, it’s backwards.) If the switch shorts to ground, or somebody replaces it with a normal oil switch, the valve draws some current and can pull down a battery in about 3 days.

Oddest one I ever saw was our church’s previous minibus, which we got free from another organization who couldn’t use it any more. Our shop did the maintenance on it for the ten years that the church had it, and we were constantly fighting a battery problem. Did put a battery cutout switch on it, allowing the drivers to easily disconnect the battery between uses.

We accidentally found the problem. At one point the heater blower switch went out, so the guys took the switch panel out of the dash to replace it, and way down behind the dash, they saw a little firefly gleam. Turned out to be a dash-type light on a little pigtail stuffed way back where it couldn’t be seen with the dash intact. It had probably been burning away, eating electrons for years.

COILS often get a bad rap. It seems obvious that a no-spark situation is a bad coil, because after all, the spark comes from the coil. I got a call from someone this morning who was suspecting a bad coil — after all, he had power to the coil, but no spark coming out.

The problem is that it takes more than just power to the coil — it takes power with a signal from the points or module to fire the coil. A coil is essentially a transformer, that takes a 6-9v current at reasonable amperage and transforms it into a high-voltage, usually 20,000v or more, milliamp spark.

What happens is that the current through the primary winding, the circuit that the points or module (also known as an amplifier or igniter) control, creates an electrical field within the coil.

The points or module then open the circuit, causing this field to collapse — and this collapse induces a high-voltage surge in the secondary winding –the one that comes out of the large terminal of the coil and eventually goes to the spark plugs. The best coil in the world is not going to fire if the primary circuit doesn’t make it fire.

In most cars, turning the ignition on and off will trigger the coil for one spark. If it does, then you can go back into the other components with your troubleshooting.

Also on LUCAS distributors, 1974 and earlier, the condition of the pigtail lead that connects the small coil wire to the points is critical. It consists of a plastic or nylon insulator block that fits into a slot on the body of the distributor and has a terminal for the wire from the coil on the outside and a very flexible wire on the inside with a terminal that fits under the insulator on the post on the points. (see below).

If the insulator is cracked, the signal that normally goes through this wire will be grounded and be lost. If the wire on the inside of the distributor is imperfect, again the coil will not get the signal to fire.

Trying to connect standard primary wire usually doesn’t work as it isn’t flexible enough (the plate that the points mount to moves as the advance mechanism does its thing, so that wire has to flex).

There are some kinds of really flexible wire that usually work, but the leads are still available fairly reasonably priced. There are two basic styles, the difference being the shape of the insulator. Both originally came in screw and spade terminals, but only the spade push-on type is currently available. According to the old books, ’61 and earlier are the early type, ’64 and up are the later type (’62–’63 could be either). We have both in stock right now.

On LUCAS distributors ’74 and earlier (and sometimes found as a transplant on newer cars), it is not uncommon for someone replacing points to stack up the pigtail (Brit: low-tension lead) and the lead on the condenser on top of the insulator under the nut holding everything to the post on the points.

This does not work. This is a dead short. The car does not run. Those leads — from the coil and from the condenser — have to touch ONLY the spring on the points and NOTHING ELSE.

In other words, they belong UNDER the insulator on the post. Any time a Lucas distributor of the 23D or 25D type doesn’t run after you’ve done a tuneup, check this out.

NEVER test an alternator by pulling off the battery cables while the car is running. It may quit, if you’re lucky, because the alternator fields are not being energized by the battery, or it may charge its little heart out trying the charge the battery that isn’t there. This is a trick that worked fine with old-fashioned generators, but that was a generation ago.

The best alternator in the world will not charge a flat or low battery. It has to have enough power coming in to energize the alternator fields. A good first step is to give the battery a long, slow charge from an outside source, and get it all the way up. If it doesn’t accept a full charge, you may have found your basic problem.

Sometimes the only thing wrong with the charging system is that something got left on and drained the battery below the line. We had a car come in that kept running low on battery power — the driver had unknowingly and inadvertently bumped the fog light switch, and her fog light covers were so dense and heat-resistant that she didn’t know they were on.

One common problem with VW, BMW, and some other German alternators is that they have rubber or plastic bushings on their mounting ears, so the case is not grounded through the mountings. Check for a small ground strap on these alternators; if it is gone, corroded, loose, or otherwise less than perfect, it can prevent the alternator from charging.

Also check the plugs in the back of the alternator to make sure they are clean, tight, uncorroded. The main power line from the alternator usually connects at the top terminal on the starter solenoid, and these connections have to be clean and tight. (The alternator and the starter are electrically separate circuits, but that solenoid post where the battery cable connects is a really handy place to connect anything that needs a good positive battery connection.) Some alternators use the warning light circuit as power source for the fields, so if this light is burned out or loose it can turn off the alternator.

Don’t forget that the starter, alternator and anything else connected to the engine is grounded through the ground strap between the engine and the body, which is usually grounded to the battery. These can get corroded or loose or fall off, and should be checked out when you are trouble-shooting an electrical failure. (Some cars have a ground cable from the battery to the engine, and then engine to body. In either case, all the ground straps need to be good.)

If the engine ground cable fails, something else will try to play ground strap, and this can cook an accelerator cable or clutch cable, or any other metallic thing connected to both the engine and the body. An accelerator cable that looks fried is a tip to check out the grounding.

Individual circuits often have their own ground connections, and these need to be clean and tight. Often these are not insulated at the factory. I recall a Mercedes with intermittent fuel injection system failure, which turned out to be an uninsulated ground connector right under the battery, with the battery leaking onto it.

Most generator-equipped British cars (pre-1970) were originally positive ground. This means that the positive post on the battery is connected to ground. This has the advantage of minimizing terminal corrosion, but it’s awfully hard to find radios that work this way any more.

(You can hook a negative-ground radio up by totally insulating the chassis of the radio from the car, and connecting the radio power lead to car ground, and vice versa. It works, but if you hit a bump and the radio touches the body, bad things happen. We had a customer do this in an older Jaguar — his girlfriend had given him the radio. She knew nothing about electricity, but insisted that he use her beautiful present.)

If the charging system is not polarized correctly for the car, it either doesn’t work or burns out the regulator. To polarize a Lucas generator, briefly connect the two posts on the generator. The only other things that are polarity sensitive are the coil (remember that the distributor is the ground, so a positive ground system has the positive side of the coil going to the distributor), and the tachometer on an MGB (which needs to be reversed internally if the car is changed to negative ground).

In the “tales from the grease pit” department: “Remember the A-H 100 that came in with the flat battery and dead electrics? I found that although the battery was still correctly connected pos gnd, someone had force-fed reverse current into it with a big enough charger that the battery became gender-confused…

“We let it trickle charge correctly for 2 days, re-polarized the generator, and it came good! It was the only case I ever saw of non-explosive reverse charging.” (Thanks to David Doiron)

I have seen a few cases of negative ground systems with a massive short go flat so fast that they lose their polarity and appear to want to work backwards. Again, the only cure is a long slow recharge.

Don’t overlook the possibility of vermin — both two- and four-legged. We just finished a wiring loom replacement, and he’d had both kind. The half-eaten walnuts and chewed wires were signs of one kind, and the way his new radio was wired in was a sign of the other.

If you have electrical problems shortly after you’ve had some electrical gizmo installed, check the installation. We once saw strange things go on in the back end of a Jaguar after somebody installed a phone in the console, and ran a long screw into the loom going to the back of the car. We have also seen problems related to alarm or radio installations.

Don’t stop looking when you find a probable cause for a problem. There is no rule that you can’t have more than one problem at a time, just like you can have measles and chickenpox at the same time.

Whenever someone tells me that “I’ve already done this, and this,and this, so it HAS to be this”, my answer is that there is no such thing as “has to be this”. It can always be something else. You’d think that a car is a straightforward mechanical/electrical object, but it is amazing how weird they can be. Almost as weird as people.

All information here is offered as suggestions only; the final decision as to any car repair is that of the installer and/or the owner of the vehicle. This information is the result of our own best research and experience, but we make no guarantees or warranties of any kind as to its applicability to any specific situation.