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Relay wiring help

12K views 7 replies 5 participants last post by  Ratrag 
#1 ·
Hoping you guys can help me understand how I would correctly wire an ignition kill switch with a relay incorporated. I know the advantages and disadvantages of killing the starter vs. the fuel pump (mine is mechanical) vs. a battery cutoff (don't want to always lose power to certain accessories) or vs. the coil (don't want the starter to be able to crank and burn up). It's a 12V system with a SBC and 80's or 90's GM column.

I believe it's desired to incorporate a relay to handle the load of the starter solenoid, but I am an electrical novice - I have searched and read and need really specific instructions. I keep seeing different and what seems like conflicting diagrams. So here it goes:

I have considered a momentary push switch and would prefer it (have to hold when turning key to start) but on the rare occasion I have to leave the car for work to be done, I don't want to have to tell them about the switch. So I've settled on a toggle-type or dual position push button on/off switch.

Is this diagram with the single relay the correct way to wire it?

If this is correct (I still need help)... Does #30 go through a fuse to the battery via an open fuse in the fuse panel? What size fuse? Does #87 go on the side of the cut wire that continues on to the Starter (should be purple, right)? Does #86 go on the side of the cut wire that goes to the column/ignition, with the switch wired inline? What size/capacity relay do I get? I see other diagrams that are similar but show each of the relay numbers going to different areas... does it matter?

On the diagram with the two relays, why does it take a second relay just for a momentary push button? Couldn't it be done with the one relay? And why are things like the ground connected from different numbers on the relay?

This is probably above me but how much more difficult is it to incorporate the horn so it sounds if the car is attempted to be started with the switch open?

Thanks for answering all my questions!
 

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#2 ·
Hoping you guys can help me understand how I would correctly wire an ignition kill switch with a relay incorporated. I know the advantages and disadvantages of killing the starter vs. the fuel pump (mine is mechanical) vs. a battery cutoff (don't want to always lose power to certain accessories) or vs. the coil (don't want the starter to be able to crank and burn up). It's a 12V system with a SBC and 80's or 90's GM column.

I believe it's desired to incorporate a relay to handle the load of the starter solenoid, but I am an electrical novice - I have searched and read and need really specific instructions. I keep seeing different and what seems like conflicting diagrams. So here it goes:

I have considered a momentary push switch and would prefer it (have to hold when turning key to start) but on the rare occasion I have to leave the car for work to be done, I don't want to have to tell them about the switch. So I've settled on a toggle-type or dual position push button on/off switch.

Is this diagram with the single relay the correct way to wire it?

If this is correct (I still need help)... Does #30 go through a fuse to the battery via an open fuse in the fuse panel? What size fuse? Does #87 go on the side of the cut wire that continues on to the Starter (should be purple, right)? Does #86 go on the side of the cut wire that goes to the column/ignition, with the switch wired inline? What size/capacity relay do I get? I see other diagrams that are similar but show each of the relay numbers going to different areas... does it matter?
I don't know where to start with this (no pun intended)....If I understand you correctly, it appears you are posting two ways to do the same thing.

If your goal is to use a relay to disable starter using either a hidden on/off toggle switch or push-on/push-off button, there are several ways to accomplish that. Here is what I would recommend:



No fuses, no connection to the battery, just a relay that interrupts the starter trigger wire, with the secret hidden switch wired to the ground side of the relay coil. This keeps things simple. The ignition switch is designed to handle the amperage necessary to operate the starter solenoid, so there is no need to power it from the battery as shown in your first diagram.

On the diagram with the two relays, why does it take a second relay just for a momentary push button? Couldn't it be done with the one relay? And why are things like the ground connected from different numbers on the relay?
There are two relays involved because this is a latching circuit. When the right side relay is triggered, it causes it to power it's own coil, keeping the relays activated until the main power from the ignition switch is turned off. This circuit is meant to be used with a momentary switch. When you turn the key on, you only have to tap the secret button once, and it disables the starter interrupt relay until the key is turned off again, then the interrupt relay resets itself.

(link to source of diagram - the12volt.com)


This is probably above me but how much more difficult is it to incorporate the horn so it sounds if the car is attempted to be started with the switch open?
You could simply splice into the wire that goes out to your horn(s) from the horn relay, and connect it to the 87a on the starter interrupt relay, and it would honk if someone tried to start it with the secret switch off.

Hope this helps....:thumbup:
 
#3 ·
Wow. Lot of info there. After reading your post about 4 times it seems the best thing to do is to explain how a relay works and that may help you out a bit. A relay is really nothing more than a switch which uses small amperage to control a load requiring large amperage. The load side of the relay which is 30 - 87 or 87a terminal can generally handle up to 30 amps without failure. The control side which is 85 - 86 operates a small electromagnetic coil which will move the internal load switch from 87 to 87a when the small coil is energized. The small coil circuit 85 - 86 usually will draw about .2 to .4 of an amp. Both circuits(control) and (load) must be protected by a fuse. The control side commonly gets a 5 amp fuse and the load side a 25 or 30 amp fuse.

The idea behind a relay is simply this...small amperage is used inside the car ie:switches(control) and larger amperage stays under the hood(load) ie: electric fan, electric fuel pump, electric choke, etc.

I am not sure what you are trying to build, but I would draw it out first nice and clearly. If it will work on paper, then start to build it on the car. I wouldn't start ripping out the original starting circuit. Maybe adapt a bit but that is all. Push button start??? Why? Is this a race car or street car? May sound cool, but not practical.

Good luck.:thumbup:
 
#4 ·
Ratrag -
Thank you. That is super helpful. I am slowly trying to understand relays.

I am not trying to install a push button ignition. I just want to install a hidden kill switch that interrupts the ignition and starter.

My understanding was that adding a switch between the ignition and starter solenoid required a relay so as not to overload the newly added switch.

So do I need the relay to be protected by a fuse as you state or would Joe G.'s diagram work safely for what I want?

Thanks!

Dan
 
#5 ·
Your ignition switch controls a relay which will send voltage to your starter solenoid. Putting a single pole switch in the ground side is fine and you would not need a fuse for that. Use a good quality switch though. By opening the switch, you will be taking away the ground for the ignition relay circuit....no start. You should be able to locate that relay in your system already and just modify the ground with a switch. No need to add another relay. It is hard to be clear by speculating on a forum, but hopefully this helps out a bit.
 
#8 ·
This is a good idea also except you have to be very aware of switch location. Because if you accidentally hit the switch while travelling it will kill the system. That may not be a good thing. At least in the ignition start circuit it will not affect the run circuit.
 
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