The primary winding of your ignition coil is the first to receive voltage from the battery. Find the resistance specifications for your car's primary coil winding in your repair manual
. Then using a multimeter, place the leads on the smaller, outside poles if you have a traditional round coil, or on the indicated poles if you have a newer enclosed unit. If the reading is within the range indicated in your manual, your primary winding is ok and you can go on to the secondary test. if it is even a little out of spec, the coil should be replaced.