[I apologize for the long reply, but I was on a roll...]
I can't remember seeing 3-prong automotive relays, but 4- and 5-prong ones
are pretty common. Bosch make the best.
These aftermarket "generic" relays are pretty simple. Inside -- on one hand
-- you have a low current solenoid designed to "pull in" when power is
applied across it. This requires two terminals (or prongs) -- one for the
power and one for ground. This circuit requires very little power to
trigger so small gauge wire will be fine.
On the other side of the relay circuit is the switch part. It is
magnetically activated by the solenoid side and also requires two terminals.
Like any switch, it is placed inline with the power going to whatever you
are switching on and off. The wiring connected to these two terminals can
vary. "Direct to ground", "direct to +12V", "hot side of load", and "ground
side of load" are all possibilities. With a 3-prong relay, it is possible
that one these two terminals could be connected to either +12V or ground,
thereby duplicating one of the two terminals on the solenoid side and making
it redundant.
Many generic automotive relays have five terminals. The four we've already
talked about, plus a fifth wired into the "switch" side of the relay. When
power is applied to the solenoid side, it pulls on the switch, closing it
and completing a circuit across the other two terminals. But when that
relay is in a "relaxed" position with no power applied to the solenoid
circuit, the switch is in a different position. Some electrical
applications could very well require the relay to transmit power when it is
"off" -- hence the need for a fifth terminal.
(5) --------+
\\\
: +------- (3)
:
(4) --------+ :
:
:
(2) ---------{ S }-------- (1)
#1 and #2 make up the solenoid-side of the circuit. When power is applied
across these two terminals (it doesn't technically matter which way in this
example), it pulls down on the linked semi-colons, toggling the "\\\" so
that it completes a circuit path between #3 and #4. When the relay is in a
relaxed state, however, with no power applied across #1 and #2, the "\\\"
bridges across #3 and #5. Many times terminal #5 is never used, and
sometimes *both* #4 and #5 are used. Occasionally, you might have a need to
use *only* #5 and leave #4 unused.
Example #1: Hooking up a set of aftermarket fog lights would require
terminals 1, 2, 3, and 4. #1 could be connected to +12V, while #2 would
connect to a toggle switch (who's other terminal would connect to ground).
#3 would also be connected to +12V via heavy gauge wire, and could
conceivably connect to #1 at the same time. Maybe your 3-prong relay does
this internally? #4 would then connect to the fog lights, which then
connect to ground.
Example #2: Fabricating a quick and dirty hi-beam/lo-beam "switch" would
involve the use of all five terminals. #1 and #2 would be hooked up to some
sort of momentary switch just like in example #1. The output from your
stock headlight switch would connect to #3, the hot side of the hi-beam
circuit to #4, and the hot side of the lo-beam circuit to #5. With a
momentary switch and your headlight switch turned on, you'd have lo-beams
for standard driving and a quick "flash" of the hi-beams at the touch of a
button.
Example #3: Ignition and/or fuel pump kill with aftermarket alarm systems
would involve terminals 1, 2, 3, and 5 (but not "4"). Many aftermarket
alarm systems come with a terminal that provides positive power to either
the ignition system or fuel pump, but only when the alarm is armed. That
signal would connect to #1, while #2 would go to ground. +12V power would
connect to #3, and then connect to the ignition system or fuel pump from #5.
When the alarm is armed, power at #1 pulls the switch away from #5, allowing
no power to reach the ignition system or fuel pump. When deactivated, the
relay is relaxed and the circuit across #3 and #5 is complete. Smarter
alarm systems (ie: less power draw) provide power at #1 when the alarm is
DISARMED, and would require using #4 instead of #5.
-James
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of asad ishaque
Sent: September 1, 2007 12:34 AM
To: [email protected]
Subject: Re: [vintagvw] 68 bug Headlight problem
While on this subject, what is the difference between three and four prong
relays??
Im comfortable with the three prong ones but the fourth prong leaves me a
little lost.
Asad.
Karachi, Pakistan.
>From: Glen Hadley <[EMAIL PROTECTED]>
>Reply-To: Air-Cooled Volkswagen Discussion List <[email protected]>
>To: Air-Cooled Volkswagen Discussion List <[email protected]>
>Subject: Re: [vintagvw] 68 bug Headlight problem
>Date: Sat, 25 Aug 2007 16:15:02 -0500
>
>In the US at least, you can pick up a 30 amp relay
>at most any parts store, no need to buy a special
>kit. They work just fine, and the previous
>instructions look good to me. I've 'relayed'
>quite a few loads, like fog lamps, etc. and
>they'll work. I would surely think they have
>these little 'ice cube' style relays there, too.
>
>glenh :<)
>
>Bert Knupp wrote:
> > Hi, Asad,
> >
> > You've already read the other replies by now. They're all correct.
>Your
> > switches and wires can't handle high amperage (current) draws. Using
> > separate power relays (Arbeitsstromrelais) is one option. There are
>also
> > several manufacturers -- both American and European -- that make
>two-channel
> > headlight relays. Your switch merely activates the channel relay, and
> > there's a direct 30 + battery feed that is then switched straight to the
> > selected headlights. I install emergency equipment (sirens, red lights,
> > blue lights, etc.) and use them occasionally.
> >
> > If you cannot find one locally, let me know. Maybe we can use the Uncle
> > Express or a similar system to get one to you. They are not expensive.
> >
> > Bert
> >
> > |__n__
> > (_____):
> > (T\_|_/T)
> > | 0 0 |
> >
> > Volks,
> >
> > I had fit a brand new headlight relay earlier for the probs I
>described.
> >
> > Still there was a smell of overheating while driving the bug at night.
> >
> >
> >
> > _______________________________________________
> > vintagvw site list
> > [email protected]
> > http://lists.sjsu.edu/mailman/listinfo/vintagvw
> >
> >
> >
>
>
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