This message was previously posted on alt.auto.mercedes,
> sci.electronics.components, sci.electronics.repair
>
> The glow plug relay on my diesel Mercedes, an 83 300SD has two sets of
> parallel contacts but only uses one because the other has a gap of about
> 0.035" when the first set closes. I thought this was due to improper
> alignment and I bent the other arm so that both would make contact. The
> other day I found another relay and noticed that it had one set of contacts
> spaced so they didn't close. Are there any experts out there that can tell
> why they do this? My guess is that the open set is a spare for when the
> first set wears too much. But that doesn't make sense because two sets
> working in parallel wouldn't wear as fast. Also would like to know if
> anyone has reversed engineered the circuit as it has an IC and a couple
> transistors. The circuit acts as monitor to make sure glow plug no. one is
> drawing current and then turns a dash light indicating that the plugs are
> heating and when it goes out in a few seconds it OK to hit the starter.
FWIW, only one set looks like full current contacts. IMO, it may be a relay used for other purposes and they don't want to run current through the light duty points.
N