Are there different types of glow plug relays ?

I was changing my glow plugs out on a 1985 300SD(5 in total) and was checking the Glow plug relay.

The glow plug harness had a connector with 5 female "holes" going to each of the glow plugs. The glow plug relay had only 4 contact points(Male) or "prongs" that connected to the glow plug harness (female) connector.

The glow plug harness fit onto the glow plug relay OK. There seemed to be no missing or broken pins on the glow plug relay.
However no voltage was going to the 5th glow plug (ie the "missing" pin)


I have had this car a bit over a year and was changing the glow plugs as the glow plug light went out and several plugs tested open.(Batt ground to connector with 5 female "holes")

Glow plug light now lights and car starts, but...