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Old 07-10-2012, 06:49 AM
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S.P.D.T. relay question

Can I use a S.P.D.T. relay to turn on a N.O.Pressure sw. when a N.C vaccum sw turns off.What I have is a 700r4 trans.,the 4th. gear pressure sw. & soli.valve are n.o. & grounded to the case.Im using a ome vac.sw. that is n.c.The vac.sw. turns it self off when engine vac. gets to7.0 ins. of vac. that when I need the relay to send voltage to the pressure sw.In other words the relay sees that the vac.sw. has turned off and now switchs on the pressure sw.Can one relay do this or is it going to take two.This is the relay w/ 87 & 87a.Im just not seeing this in my head.

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Old 07-10-2012, 08:19 AM
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I do not quite understand your exact needs about want you want to happen, but I think I can help.
If the switch is on, and you actually want an off condition, hook the switch to the coil, and hook the load to the 87A pin on the relay. 87A is NC, (on) without the coil energized, so if power is applied to the coil, 87A is open.
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Old 07-10-2012, 06:35 PM
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I think I do understand what you're saying, and DanielC is right on the money.

I would do it like this:


Hope this helps.....
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Old 07-10-2012, 07:02 PM
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Yes,it hard to explain.The trans needs to go into lockup at higher vac.such as above 8 ins.of vac.The OEM vaccum sw. (n.c.)will only turn on at low vac. 0 to 7ins of vac. Then when you have hammered the gas,vaccum drops below 7ins.of vac then turns on the OEM vac. Sw. thus sending voltage to relay to turn off voltage to pressure sw. & soli.valve,(n.o.) Thus turning off lockup.Then when your back to steady cruise vac. goes above 7ins. of vac. OEM vac sw. turns off,relay sees no voltage an turns on pressure sw. & soli. valve an now were locked up againe.So in short OEM vac.sw. (n.c.) im guessing will be connected to n.c. contacts of relay? And pressure sw. & soli. valve (n.o.) will be connected to the other contacts on relay.I guess I should of spended the 100.00 or so for the kit,yes...yes.. I know I should have done it,but its like everything I do ” the hard way”.
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Old 07-10-2012, 09:10 PM
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Quote:
Originally Posted by dogwater View Post
....So in short OEM vac.sw. (n.c.) im guessing will be connected to n.c. contacts of relay? And pressure sw. & soli. valve (n.o.) will be connected to the other contacts on relay.
Nope. The vacuum switch switches the relay's control (coil) circuit (terminals 85 and 86). The pressure switch and solenoid get their power from the relay's NC (87a) terminal.

In the diagram above:
Relay terminals 85 and 86 are the control circuit. If you power one and ground the other, it will trip the relay.

Relay terminals 30, 87, and 87a are where the work is done. Terminal 30 is known as the "common" terminal. When the relay is not tripped, terminal 30 is internally connected through the relay's contacts to the 87a (NC - Normally Closed) terminal. When you 'trip' the relay, the 30 terminal's internal connection changes from the 87a to the 87 (NO - Normally Open) terminal.

In this case, fused key-on power is supplied to both the 30 and 86 terminals. The 85 terminal gets grounded when the normally closed vacuum switch senses vacuum less than 8 inHg. During this low vacuum condition, the relay is tripped, and sends power from the 30 terminal to the 87 (which isn't connected to anything). Meanwhile, the 87a terminal (which is connected to the trans switch) is dead.

When the vacuum increases to the point that the NC vacuum switch opens, the relay coil loses it's ground and the relay un-trips. When this happens, power supplied through the 30 terminal is passed to the 87a (NC) relay terminal, thus sending power to the transmission pressure switch. If the transmission pressure switch is also closed, power passes through it to the lockup solenoid, engaging it.

Hope that makes sense...

Good Luck

Last edited by Joe G; 07-10-2012 at 09:17 PM.
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Old 07-10-2012, 09:33 PM
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Painless #60109 is the whole kit.

The installation manual makes no mention of a relay.

Just a thought ...
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Old 07-11-2012, 06:02 AM
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Thank you JoeG.Working with relays & normaly closed & open switchs makes my head spin. Funny thing is I helped the electriction wire in the house I had built a few years ago,it hasnt burned down just yet.
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Old 07-13-2012, 07:50 PM
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I just got around to reproducing this on my work bench & it worked,I used a blinker bulb as my pressure sw.One other question , my Camaro did come with cruise control that was turned on & off by the brake sw.To cut power to the relay should I use no.30 or no.86 on the relay.The cruise control is out of the car.Thanks for your time.
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Old 07-14-2012, 04:08 AM
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Depending on how you have it wired, removing power from terminals 85 or 86 will de-energize the relay

Terminals...

30 common
85 one side of the coil (either Pwr or Gnd)
86 other side of the coil (either Pwr or Gnd)
87 Normally Open (when relay functions connects with 30)
87a Normally Closed (Is connected to 30 untiil the relay functions)
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Old 07-24-2012, 09:02 PM
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lighting relay

I dig what you are doing - but there may be some people reading this that will grab a lighting relay instead of the one to which you refer....

In which case both of the terminals 87 and 87a will be NO (normally open) and will close when the coil is energized. If the one they pick up is an "unknown" - ought to check it out before having a problem.
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Old 07-25-2012, 03:44 AM
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"In which case both of the terminals 87 and 87a will be NO (normally open) and will close when the coil is energized."?

It has been my expr that if a relay has dual out puts both terminals are labeled 87a or 87b or just 87........ I have never seen a relay where it had dual out puts (both terminals are NO or NC) and labeled 87a and 87
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Old 07-25-2012, 10:38 AM
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mY BAD

YOU ARE CORRECT THE COMMON SWITCHED RELAY TERMINALS ON THE LIGHTING RELAY WILL SHOW AN "87" AND "87b"........

The TROUBLE usually comes from the tiny "87a" and "87b" embossed on the black plastic - and old guys like me with bifocals......
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Old 07-26-2012, 11:41 AM
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This relay has two 87 pins.
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Old 07-26-2012, 04:24 PM
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And your point would be?
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Old 07-26-2012, 04:33 PM
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Maybe someday when you are wiring up two headlights to one relay you will figure it out.
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