powering relays and switches

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=120624
Printed Date: July 21, 2025 at 11:23 PM

Topic: powering relays and switches

Posted By: gbodyera
Subject: powering relays and switches
Date Posted: March 09, 2010 at 10:22 PM

I currently have 2 relays in my engine compartment. 1 elec. fan. 1 fuel pump.
Currently I have power from both relays and power from both of their switches going directly to the positive battery terminal. This is just temporary while breaking in my engine. Its not really pretty or smart.

I also plan on wiring in a few indicator lights to the switches which is simple.

Whats a cleaner solution to getting power to everything?

I was thinking of having them powered off of an accesory wire but dont know how. I think they may just drain batt power how they are now.

Replies:

Posted By: howie ll
Date Posted: March 10, 2010 at 1:50 AM

Power the switches from an ignition circuit to trigger the relays. You can feed your indicators from either the switches or the relay outputs. Leave the relays fused from the battery.

Posted By: tommy...
Date Posted: March 10, 2010 at 8:00 AM

Are the relays under the hood "protected" at all...(from weather)...Ignition would be a good source of power...Power when the key is on and cranking...! Accessory if you want power to cut out during cranking...! What type of vehicle is this...Might get some clearer answer's/tech tips.... Here is a basic diagram for switches and relays...It is hooked to constant...but obviously can change source(s)... https://bcae1.com/swrelay.htm

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M.E.C.P & First-Class
Go slow and drink lots of water...Procrastinators' Unite...Tomorrow!

Posted By: gbodyera
Date Posted: March 10, 2010 at 10:41 AM

Its in an 82 Olds Cutlass Supreme

I know how to wire them. I just dont know exactly which wire to use and how?

both of you guys mention ignition power. So so I just splice into the ignition wire in 2 spots (1 for each switch)? I know the ignition wire is on the column, what color is it?

You also say leave the relays wired how they are, directly on the positive batt terminal. ok.

Please correct me if Im wrong.

Posted By: howie ll
Date Posted: March 10, 2010 at 11:54 AM

Can't tell you the colour, but test, it will show 12 volts+ when the ignition is turned to on.
Yes tap off this wire, as a double safety I'd tap (solder into it) once, place a 3amp fuse in line, then split in two, one for each switch.
Tommy made a good point about mounting the relays. Always mount them terminals down. Also I spray with lithium grease or a water retardent. The ultimate for longevity would be a sealed plastic box, grommet the cable entry and seal this with RTVC. You can buy the box from Radio Shack etc.

Posted By: tommy...
Date Posted: March 10, 2010 at 6:42 PM

Here are the colors of the wires...What is the fan for...Do you want the fan to shut-off during crank...If so...Tag power for that at Accessory and the other at Ignition...There is no reason to have them hooked to a constant 12v unless you are using either with the key Off...If only used when car is On or running...Then Ignition for On during Crank and Start... and Accessory for Off during cranking , On with start(like a radio)...Make sure it's fused properly...And you can use the negative for the switch...Instead of positive...

Battery	RED	(+)	IGNITION SWITCH HARNESS...These will be thick wires...Verify with a meter...!
Ignition 1	PINK	(+)	IGNITION SWITCH HARNESS
Accessory 1	ORANGE	(+)	IGNITION SWITCH HARNESS

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M.E.C.P & First-Class
Go slow and drink lots of water...Procrastinators' Unite...Tomorrow!

Posted By: gbodyera
Date Posted: March 10, 2010 at 9:38 PM

i have the fan on my radiator with a temp sender hooked to it. i only have the switch wired into it as a manual override. thats just in case i want to run it when the car's not running for extra cooling.

Posted By: howie ll
Date Posted: March 11, 2010 at 2:33 AM

Isn't there an Otter (thermal switch) for the cooling fan?. If this goes to ground (it doesn't matter if it's 12V+ either) just parallel it back to a switch, that switch can also turn on an indicator. We used to do this all the time on Jensen Interceptors in the 70s.
If I didn't make myself clear, whatever triggers your fan relay now.

Posted By: gbodyera
Date Posted: March 11, 2010 at 10:28 AM

just 1 thermal switch in the intake manifold. triggers the fan at set temps.