Yeah, it might be a nerdy gearhead thing, but as enthusiasts we want a lot of information about what our cars are doing. Unfortunately, the manufacturers don't quite see it our way, so cars are equipped with instrument clusters about as informative as a utility company's customer-service recording. We understand--they have to make cars for people who care more about their appearance in the rearview mirror or the latest tweet from the Kardashians. Bummer, because there is way more cool stuff going on under the hood than on reality TV. If you're saddled with a car bereft of all but the most basic instruments, you're going to want to add some gauges. Most people start with a tachometer, and that's exactly what we did, but how do you hook one up to the car's distributorless ignition system? We're glad you asked. Electronic Ignition Tach: How It Works In a Distributorless Ignition System (DIS), each coil is responsible for firing one or a pair of plugs, so they fire less frequently. This allows the coils more time to charge up, meaning they are able to deliver a hot spark, even at high engine speeds. In addition, electronic control allows for very precise spark timing. In the case of the coil on plug ignition in our Crown Victoria, system voltage is fed straight to the coils via a relay near the battery. A single wire from this relay ends in a splice near the top of the engine, from which eight wires branch out to the individual coils,through the primary windings of the coils and out into eight more wires that go to the ECM, which provides the ground path for each coil. With the key on, current is flowing through the relay, the coils, and to the ground path provided by the PCM, energizing the primary windings inside the coils. To cause the spark plugs to fire, the PCM breaks the circuit to each coil individually according to the engine's firing order, stopping the current flow. This causes the energy built up in the primary windings to jump to the secondary windings, which are made with loops of much finer wire. The smaller diameter allows much more wire than that used to make the primary windings. The result is a multiplying effect, as a system voltage of 12 to 14 volts increases to nearly 40,000 volts, or enough to jump the gap of the spark plug. The electronic ignition tach adapter reads the amount of current passing through the system as the engine is running and generates an analog signal readable by most aftermarket tachometers. That signal comes out on the grey wire. Parts Description PN Source Price VDO Performance electronic ignition tach 333 942 eBay Motors $25.50 Autometer electronic ignition tach adapter 9117 Summit Racing 73.95 40-watt soldering iron 3055439 Fry's Electronics 34.95 Rosin-core solder 4455316 Fry's Electronics 2.49 Total $136.89 Always set the redline near 7,000. This tachometer comes with a five-wire pigtail, -12V power, ground, a signal from the distributor, illumination, and illumination ground. Power and ground are easy to hook up, as is the distributor signal, as long as you have a distributor. But in cars built since 1997 (or so) with distributorless ignition, you need an adapter. This tachometer comes with a five-wire pigtail, -12V power, ground, a signal from the dist The illustration MSD provided (above), shows the adapter wired in series to a single coil. But, our VDO tach can’t read the signal from just one cylinder and accurately interpret it to display engine speed for all eight, so we needed to wire the adapter into the wire that feeds all eight coils. In the case of our Crown Victoria, we cut this wire (circuit 34 coming out of connecter 1026) just before the splice where system voltage branches out to each coil. Power then goes into the adapter’s red wire, through the adapter, and out to the car’s ignition system via the red/green wire. The illustration MSD provided (above), shows the adapter wired in series to a single coil. If our Crown Victoria had been totally optioned out, we would have had buttons for the height-adjustable pedals and traction control in this piece of trim next to the steering wheel. Even though our car doesn’t have those options, the connectors are still there, giving us a convenient source for 12-volt power for the tach and dashboard illumination (those buttons would normally illuminate with the gauges). We removed each of those wires from the connector and attached them to the tachometer. The gray wire from the adapter connects to the tach’s green wire. We grounded the tach to a nearby ground on the steering column. If our Crown Victoria had been totally optioned out, we would have had buttons for the hei Before mounting the tachometer, we made sure it was calibrated for eight cylinders. These three small slider switches can be adjusted to also read four- and six-cylinder engines. Before mounting the tachometer, we made sure it was calibrated for eight cylinders. These Note that we chose to solder all the connections and cover them with heat-shrink tubing. This ensures 100 percent connectivity and a weatherproof seal. Note that we chose to solder all the connections and cover them with heat-shrink tubing. T After much thought, we decided to mount the tach here rather than on the A-pillar or on top of the dashboard. It completely covers the coolant voltmeter and partially covers the fuel-level gauge. That’s OK, we’d be able to tell if the battery is about to die. After much thought, we decided to mount the tach here rather than on the A-pillar or on to Using some short sheetmetal screws, we permanently mounted the adapter to the driver-side wheel liner and zip-tied the wires together. Using some short sheetmetal screws, we permanently mounted the adapter to the driver-side SOURCES eBay Motors http://hub.motors.ebay.com/ Auto Meter Products 413 W. Elm St. Sycamore IL 60178 815-899-0801 www.autometer.com By John McGann Enjoyed this Post? Subscribe to our RSS Feed, or use your favorite social media to recommend us to friends and colleagues!