just another relay question...

wannabe

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Aug 31, 2009
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since I can not open the pics on the relay post, I am forced to ask yet another boring question. I have tried to look at every aspect of the use of relays and have come up with an observation on the orientation of the way to wire up the five terminal relay. 30, 85, 86, 87 and 87a. the way I see it is, the relay does not care, to some extent, which way it is wired. as in 30 or 87 can be power in and the other, power out, while 85 or 86 can also be either power in and ground out on the other. now if not using 87a terminal, it can be totally left out of the equation, but, if you use 30 as power in, 87a will have power on when the acc is turned off. if 87 is power in and 30 power out, then 87a will not have power when the acc is turned off, correct? my plan is to power in 87, jumper lead over to 85 or 86 and power out of 30, using the ground for on/off switch lead. sorry for not using the correct technical terms, but it is what it is...thx, wannabe
 

Doober

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Jun 2, 2003
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85 and 86 are only the trigger, they do not carry any type of load... I'm not 100% sure that's what you mean though. 30 connects to either 87 or 87a, depending on if the relay is energized or not. If the relay has a layout of the terminals, it should show you which terminals are connected with power off. Yes, you can run power off your constant power lead (i.e. terminal 30) and pigtail to 85 or 85, then run to a switched ground.
 

wannabe

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Aug 31, 2009
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yeah, the 30 terminal is connected to the 87a, when not switched on for the acc, so as long as there is power to the relay, 87a is hot, which can be insulated but if power comes thru the 87 and out thru 30 then the 87a will be dead when switched off. probably not a big deal, just trying to make sure I get it right and as safe as possible the first time. thanks for the reply doob...wannabe
 

LS6 Tommy

MalibuRacing Junkie
May 15, 2004
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The way you want to have it will work just fine in terms of switching, but you should feed your load from the battery, not from the switch that goes to 86/"trigger". Also. 86 should always be 12VDC+ and 85 ground. Many relays have a diode between 85 & 86 that will get blown if you reverse the polarity.

Normally, terminal 30 is "common" (from battery), 87 is "normally open" ("hot" only when the relay is energized) and 87a is "normally closed" ("hot" when the relay is not energized & "dead" when the relay is energized). When you use 30 as the common, you can use the relay to switch between two different items. An rough example would be 30 is fed from your fog light relay. 87 feeds driving lights & 87a feeds fog lights. 86 could be tied to your high beam switch to automatically switch from fog lights to driving lights when you turn your high beams on.

Tommy
 

Doober

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Jun 2, 2003
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Aaaaaand you can do lots of cool little things with relays :D

I haven't wired an alarm in the '78 yet, but plan on a hidden siren or 2 in the cabin. When the alarm is armed, instead of the 30 terminal being constant 12v, it will be ignition switched, so when the alarm is armed the circuit is closed between the siren and ignition switch... would-be thief turns the ignition on, and the siren is constant until the ignition is turned off.
 

wannabe

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Aug 31, 2009
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Tommy/Doob, I think I understand at least part of your explanation. I will use 85 as my switch/ground, power in to 86. I don't know if the relays I am using (tyco/bosch) have a diode but in any case, better to be safe than sorry. I still plan to use 87 as power in and 30 as power out to acc. it is just a better approach as far as putting together a neater appearance, as far as the wiring harness goes. Doob, you got a little over my head with the alarm wiring, I tend to use the kiss principle. if this is not acceptable, please continue my education. thx for help given...wannabe
 

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