relay wiring diagram needed

Printed From: the12volt.com
Forum Name: Relays
Forum Discription: Relay Diagrams, SPDT Relays, SPST Relays, DPDT Relays, Latching Relays, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=80936
Printed Date: May 15, 2025 at 6:10 PM

Topic: relay wiring diagram needed

Posted By: edmitchell
Subject: relay wiring diagram needed
Date Posted: July 29, 2006 at 1:20 PM

Relay added to antique car for fans by amatuer (me). #30 constant power #87a constant power but not being used #87 load to fans #86 to thermo switch which completes ground and turns on fans #85 is hot only when key is on . Car has push button to start after key is turned on. I want the fans to shut off momentarily while cranking car but thermo switch is still activated because car is still warm. Also do not want fans to stay on after key is shut off which works correctly now. Need rookie expllination. Thanks

Replies:

Posted By: the12volt
Date Posted: July 29, 2006 at 1:27 PM

Add another SPDT relay. 85 to output of push to start switch, 86 to ground, 87a from this relay to 87 of your first relay, 30 to fans.

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Posted By: edmitchell
Date Posted: July 29, 2006 at 8:04 PM

Thanks a lot for help, I will try your solution . Ed

Posted By: edmitchell
Date Posted: August 01, 2006 at 1:34 PM

No luck, same problem. Fans still come on during cranking of motor if temp. between 180- 205 from thermo switch.

Posted By: the12volt
Date Posted: August 01, 2006 at 1:38 PM

The additional relay is just to interrupt power to the fan during starting. Please post all connections you have for each relay connected from the power source to the relays then to the fan.

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Posted By: edmitchell
Date Posted: August 01, 2006 at 3:48 PM

Original relay #30 Direct hookup to alternator (fused) always power . #86direct hookup to thermo switch ( ground at 200 opens 180). #85 direct to fuse panel, only hot with key on. #87a empty. #87 first relay hooked to second relay 87a. #30 second relay direct to fan. #87second relay direct to starter where starter button hooks up , open until starter button pressed. Hope this helps .

Posted By: the12volt
Date Posted: August 02, 2006 at 11:00 AM

87 of the second relay should not be used. Move that lead to terminal 85 as stated in my original reply. Here's how they should be wired.

Relay 1
30 to 12V+ (constant)
87 to 87a of Relay 2
87a not used
86 to thermo switch ground output
85 to ignition (12V+ when key is on, not an accessory lead)

Relay 2
30 to fans
87 not used
87a to 87 of Relay 1
86 to ground
85 to starter (12V+ during start)

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Posted By: edmitchell
Date Posted: August 02, 2006 at 2:05 PM

PERFECT, Thanks Ed

Posted By: the12volt
Date Posted: August 02, 2006 at 8:58 PM

You're welcome ;)

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