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Unread 08-26-2014, 02:04 PM   #1
TexAg09
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Question about relays

1984 CJ7 258 I-6

I am installing a 3 switch panel on my dash. Running a toggle switch for ignition, push button start, and accessory toggle switch. It says it is a 40 amp switch.



How many relays do I need to install going to this panel?

I was thinking that if I put a 4 pin, 40 amp relay on the supplied power, that might be all I need.

Also, where is a good place to get the relays from? I can't seem to find more than one at my local parts stores. Plus I know they are cheap on the internet and I don't mind waiting on them. This is all new to me so anyone with any expert advice would be greatly appreciated.

I just installed the Painless 10110 wiring harness and this is the last step I have to get my jeep back on the road.

I know it is not what most guys would do, but I like the idea of having a push button start. The PO didn't have a key to the column and all my internals of the column as well as ignition switch were shot. I bought this switch panel and also am installing a keyed kill switch on the battery terminal for a little bit of protection. This is just a trail rig/hunting rig so I'm not looking to spend a bunch on new/rebuilt column, lock cylinder, etc.

Thanks in advance

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Unread 08-26-2014, 02:37 PM   #2
CSP
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I'm not sure where you think you need a relay with that schematic.

Or why a relay is needed. There aren't any relays for those circuits using the stock ignition switch.
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Unread 08-26-2014, 02:43 PM   #3
TexAg09
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When I contacted painless, they told me I needed a relay going to the switch.

I was thinking the same thing about not needing a relay, but I wanted to see what the consensus is before messing something up. I've spent a lot of time and effort so far and don't want to mess it up.
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Unread 08-26-2014, 02:45 PM   #4
Mike Romain
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I can't see you really needing a relay with a 40a switch. The stock key switch has none. Your output from the various switches needs to be full power.

You could set up each circuit on a relay and just use the switches to trigger each relay, but that is just more parts to go bad some day. Folks do that when they want to run low amp micro switches to turn on big power. You are using big power switches already.
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Unread 08-26-2014, 02:53 PM   #5
TexAg09
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Thanks Mike. It was just a precaution and wanting to be sure before messing something up.

This electrical is all new to me.

If someone else needed a diagram for what wires go where, there ya go. I used the Joe's Racing 46100 switch panel
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Unread 08-26-2014, 03:28 PM   #6
CSP
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I agree with Mike and don't quite understand why Painless would suggest that, other than they might think you're using a common parts store switch which doesn't have a very high rating.

I also believe that the correct way to put it would be that a switch would be used to trigger a relay rather than a relay going to a switch.

The former means the relay is downstream of the switch and the latter means the relay is providing power to the switch.
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Unread 08-26-2014, 04:00 PM   #7
JeepHammer
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Depending on wire size and switch capacity, you probably don't need a relay in the 'Start' circuit/push button.
The starter relay on the fender will need about an amp capacity, and most common automotive switches will handle that.

IF you have a factory ignition, you are looking at about 3 amps, so again, most common automotive switches will do that job.

Accessories are another story.
Since you didn't give a list of the things you want to hook up to 'Accessory' we have no idea how much of a load you are going to draw.

High draw will need a relay, low draw won't.

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Unread 08-26-2014, 04:12 PM   #8
TexAg09
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No accessories right now. Will install radio at later date but as of now, nothing.

Thanks for the direction guys
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Unread 08-26-2014, 04:23 PM   #9
dirtdudeaz
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If you connect all your power in series and add a 12V source to it in the beginning, then technically you are reducing the system to a 2-switch system: "ON" and "Start". You would be able to turn over the engine and not be able to get it running if the accessory or ignition switches are off.

These may help...or maybe they don't. Second one is from John Strenk.
untitled1.jpg  
ign_switch.jpg

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Unread 08-27-2014, 09:30 AM   #10
Ken4444
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Since you're new to electrical, keep in mind what a relay does: It is just a switch that is turned on/off by another switch or circuit. Literally, the mechanism "relays" (or switches) your control (on/off) to the other circuit.

Why are relays needed then? Classic example: If you have a high amperage circuit like headlights or a light bar full of lights that create a large electrical load, and you want to switch the lights on/off with a smaller (low amperage) switch, or a switch that can't handle the high electrical load of headlights, then you let the relay do the switching of the lights, and you use your small/tiny/low-amperage switch to turn the relay on and off. One benefit to this (the heeadlight scenario), is that you can avoid having to run thick gauge electrical wires all the way to the on/off switch. Instead, all of the big wiring hits the relay, and you use smaller/thinner/lower amperage wires to switch the relay on and off.

As has been posted already, if you have a 40 amp switch then that is heavy duty and you would be less likely to need a relay in the circuit. I think automotive relays are typically found in amperage ratings of 10 to 50 amps, so your 40 amp switch would take the place of most relays.
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Unread 08-27-2014, 09:35 AM   #11
CSP
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Voltage drop is probably a bigger reason to use relays.

With the light example if you have a switch that can handle the load you're running a long distance of wire from the battery to the switch and then back out to the grille area. With a relay the main power feed can go straight from the battery to the lights, eliminating a lot of wire distance which equals voltage drop from one point to the end.
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Unread 08-27-2014, 09:47 AM   #12
Ken4444
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Quote:
Originally Posted by CSP View Post
Voltage drop is probably a bigger reason to use relays..
Good point. When you're only starting with 13 or 14 volts, even a 5% drop in voltage equates to over half a volt loss. Lose 20% of your voltage and you've gone from 14 to 11 volts. With lighting, that equates to dimmer lights which goes against the point of the lights in the first place
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Unread 08-27-2014, 09:57 AM   #13
grasmo
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Quote:
Originally Posted by CSP View Post
Voltage drop is probably a bigger reason to use relays.
this is not correct at all. you did say probably though.
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Unread 08-27-2014, 09:58 AM   #14
CSP
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So in your opinion, what is correct?
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Unread 08-27-2014, 10:05 AM   #15
grasmo
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there is no opinion as to what a relay is for. it's a switch that uses a low current circuit to CONTROL a high current circuit.
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