Here is a problem that occurred when I added a "slave relay" to my
82 Westy Diesel starter circuit.  I've looked in the archives and seen
the issue of using a relay, or "solenoid" to avoid excessive voltage
drop key-to-starter discussed, but did not see any mention of rapid
failure of the diesel glow timer relay after.

    After experiencing several failures of the starter to engage(only a
slight click upon turning the key) I checked the voltage at the starter
solenoid terminal and found it less than 8 volts.  I obtained one of
those old style, ford truck type "starter solenoids" (actually a relay)
which is meant to take the small current from the key and use it to
actuate a very big switch  which handles the high current  from battery
to starter.  The wire that led to the starter from the key was wired to
the "solenoid" and the terminals on the solenoid were wired from the
battery to the terminal on the actual starter solenoid.  All was well as
the starter now engaged instantly since it had the full battery
potential delivered to its' internal relay and pull-in coil.

    About  6 starts later, the glow plug relay failed in the ON mode and
I had to quickly open the back deck, pull the relay to avoid destroying
the glow plugs.  Replaced the glow relay.  Same thing, only in the OFF
mode.  Can you guess what is happening?

    When I installed that big ford "solenoid"  I  had not considered
that  it would generate a huge voltage spike when the field collapsed at
turn off.  Each time I started the vanagon, that spike went downline to
the SOLID STATE glow timer relay and soon destroyed a  tiny part in it.
The problem was solved by adding a diode, connected from the ford
solenoid switch terminal  to ground.  The 200 volt, 1 amp diode blocks
normal current flow but allows the back voltage from the coil switching
off to go harmlessly to ground.  This is called a "clamping diode", I
believe.  I could have saved some grief by using a $6  VW load reduction
relay as most of these have the diode built in, I'm told.

    Gas  vanagons have a lot of solid state parts too  and could suffer
such mystery failures if an unprotected relay is similarly used.

Thanks to all  and hope you can use the info

Ed Lowe
82 Westy Diesel
85 Golf Diesel
92 Cabrio