re: Relay Problem

["Tony Sims" <simstony@domain.elided>]

No disrespect intended to Dean Cains, but I'm guessing from reading the note
below that Ralph's car has a relay that was installed to provide power to the
Bosch fuel pump in the rear of the car near the tank, that feeds gas to the
Spica injector pump, rather than to any of the electrical components of the
Spica injector pump itself.  IIRC, this is a pretty common modification, as
the wiring feeding the pump is a little undersized and with the length of the
run, the voltage drop leaves the pump with less that 12v to run on.

I don't know how many amps that fuel pump draws, so I can't say for sure if
the relay is too small, but depending on where the relay is mounted, the gauge
of the supply wire to the pump and the distance it runs, either the heat or
the voltage drop could be stressing the relay.  Once you determine your wiring
is OK, it would be cheap to swap in a 30 amp relay, and that should be big
enough for the job.

Ralph, without more info on how the relay is wired, it's tough to say if it is
correct, but I can offer my opinion on how it could/should be wired.  One
option -- the original power wire to the pump would be the "switch" wire for
the relay, going to the 86 terminal on the relay.  The 85 terminal should be
to ground (earth).  The high-power source (battery or alternator) should feed
into the 30 terminal, and this feed to the relay should include a fuse or
circuit breaker.  The 87 terminal feeds power to the pump positive (+)
connection.  Then the pump ground (-) connection goes to ground.  The wire to
the 30 terminal and from the 87 terminal to the pump should probably be 12awg
to be sure you are delivering a full 12v, as should the pump ground wire.

Another option, which would be safer in an accident, would be to choose a
"switch" power source (the wire to the 86 terminal) that's only hot when the
engine is running.  That way if you have an accident that kills the engine,
the relay shuts off the fuel pump and it won't pump gas from a broken line.
Right off the top of my head I can't think of a source for this on a '74 GTV.
Hot rod suppliers sell fuel pump shut off kits that provide this safety kill
function too.  Simpler and somewhat better than the original circuit would be
to put a switch in the cabin for the fuel pump, so you could shut it off.

Hope this helps.

Tony
74 GTV 2000
70 2800 CS
72 Bavaria (the grosser berlina...)


At 04:33 PM 8/25/2002, you wrote:
>Date: Sun, 25 Aug 2002 14:34:43 -0400
>From: ralphone@domain.elided
>Subject: Relay Problem
>
>I'm the proud owner of a great 74 GTV which I plan on using as a daily
>driver.   I noticed the PO installed a Relay for the Spica Fuel Pump.
>The relay is Bosch rated at 15A.  I noticed the relay is always pretty
>hot to the touch. I was wondering if the relay was rated to small for
>the FI pump or are the wires screwed up?
>
>Thanks in Advance.
>Ralph DeLauretis
>1974 Alfa GTV
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