There are two types of glow plugs used on General Motors Corp. diesels; the fast glow type and the slow glow type. The fast flow type use pulsing current applied to 6 volt glow plugs while the slow glow type use continuous current applied to 12 volt glow plugs.
An easy way to tell the plugs apart is that the fast glow (6 volt) plugs have an 5 / 16 in. wide electrical connector plug while the slow glow (12 volt) connector plug is 1 / 4 in. wide. Do not attempt to interchange any parts of these two glow plug systems.