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Help!! Wiring relays

Old 10-10-2018, 08:18 PM
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Default Help!! Wiring relays



Working on a 1982 C10 carbureted 6.0L swap. Need help wiring relays for the fuel pump, fans, and 6014 msd box. Do i need a relay for each one?? The relays I have has
1- purple wire for power to the acc
1-yellow wire to ignition source
1- red wire to battery
1- gray wire to ground
Seems simple to me wiring one. But do you wire all 3 the say way?? Thx for any help. If more info needed let me know.
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Old 10-11-2018, 06:33 AM
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A relay for each of those is definitely not a bad idea. The wire colors don't mean anything, you need to look at a wiring diagram. Pretty simple, but the arrangement of contacts can be different with different relays. Fans will need a larger relay than the box or fuel pump

Make sure you put a fuse in the main power wire up stream of each relay. Thus good idea to run the power wires straight to a common fuse box. .
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Old 10-11-2018, 10:53 AM
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I don't like using relays on anything that draws 15 amps or less. Unless your using low amp switches. More connections more chances for problems. We run a A3000 fuel pump. It only draws 10 amps. Fans each draw 10 amps. Ingnition box only draws 8-10 amps. Electric water pump 10 amps. Have always done it this way and have never blown a fuse. Street drive too. We have all that on 20 amp switches with a 20 amp fuse to each. The Moroso switch panels. I label each wire 3 to 4 times depending on length. So if you do have a problem it's very easy to isolate and fix it.
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Old 10-11-2018, 11:09 AM
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Hmmm!!🤔 thatís something I will look into, Preciate it!
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Old 10-11-2018, 05:25 PM
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Most standard automotive relays are 30A, so quite adequate for each of the things you mention.

Whoever is suggesting a cooling fan only pulls 10A...must be running one hell of a small fan.

Relays are a simple and safe way to switch devices off and on, and to reduce wiring for heavy loads. So yes, in many cases they are a good idea. Relays are quite simply a form of remote switching where the switch you use is not designed to carry heavy loads.
And always fuse circuits appropriately etc etc
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Old 10-12-2018, 01:40 AM
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Originally Posted by stevieturbo View Post

Whoever is suggesting a cooling fan only pulls 10A...must be running one hell of a small fan.

c
We run low amp 2200 cfm 12" fans. I'm sure on start up they pull a few more amps but while running they only pull 10 each. Two of them side by side each on their own 20 amp switch with 20 amp fuse. Have never blown a fuse ever. Hook up the battery charger when back to the pits and the fans and the electric water pump run till its cooled down after every pass. Not to mention street driving. Works perfect. I know that reading values on a particular item is highly over rated. But look at electric fans and you will see. Like I already said. Nothing over 15 amps. Gives you a little buffer with a 20 amp switch and fuse.
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Old 10-12-2018, 05:02 AM
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Are you turning everything on manually or using the ignition to turn them on? I wouldn't run all of that stuff directly off the ignition - use relays.
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Old 10-12-2018, 12:27 PM
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I know this will sound odd but use you ignition wire to run another relay to turn on the rest of the relays. In industry this is called relay logic, or use the one wire off the ignition and daisy chain them together(will look like a bunch of U’s between them.). Relays only draw .2 amps each, so 5 relays= 1 amp to pull in all the coils. Do not put them all on one relay this is a no no. Say your fans short and go straight to ground and you have a 50amp fuse on the one circuit the fuse may not blow than you will have a wire fire. You can get relays for dirt cheap it is not worth the risk.

If you have any questions about it pm me I do this for a living in an industrial setting.
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Old 10-12-2018, 02:37 PM
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Thanks for the info guys, really helps me decide what route to take💪🏾
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Old 10-13-2018, 04:29 AM
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Originally Posted by 8.Lug View Post
Are you turning everything on manually or using the ignition to turn them on? I wouldn't run all of that stuff directly off the ignition - use relays.
Yes we are turning everything on manually. If you want to use your ignition switch you just use one relay that will hold enough amps for all the accessories. We use the Moroso switch panels. We don't use our key switch due to it is a crummy switch with a lot of noise for the electronics. Relays create noise too.


[QUOTE=goober35;19984393]
I know this will sound odd but use you ignition wire to run another relay to turn on the rest of the relays. In industry this is called relay logic, or use the one wire off the ignition and daisy chain them together(will look like a bunch of Uís between them.). Relays only draw .2 amps each, so 5 relays= 1 amp to pull in all the coils. Do not put them all on one relay this is a no no. Say your fans short and go straight to ground and you have a 50amp fuse on the one circuit the fuse may not blow than you will have a wire fire. You can get relays for dirt cheap it is not worth the risk.

That's the whole point of running proper sized fuses to each item. Just like you would with any relay. You ever had a bad relay, one that would cut out when hot but work when cold. Or just one that cuts in and out due to a weak coil. Or how about the worst, they hang in when you kill the switch. So many possibilities for failure. Have seen every one of those scenarios. Its not worth the chance to me. I want to know when I flip that switch its on or off. Too many connections. Plus how do you connect them. Butt connectors. More noise, resistance and possibility for failure. I soldier and heat shrink everything only. What is the biggest problem in the pits. Electrical. Nothing is perfect but I have found this is the least way to having any problems.

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Old 10-13-2018, 11:16 AM
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[QUOTE=TTur1996;19984774]Yes we are turning everything on manually. If you want to use your ignition switch you just use one relay that will hold enough amps for all the accessories. We use the Moroso switch panels. We don't use our key switch due to it is a crummy switch with a lot of noise for the electronics. Relays create noise too.


Originally Posted by goober35 View Post
I know this will sound odd but use you ignition wire to run another relay to turn on the rest of the relays. In industry this is called relay logic, or use the one wire off the ignition and daisy chain them together(will look like a bunch of Uís between them.). Relays only draw .2 amps each, so 5 relays= 1 amp to pull in all the coils. Do not put them all on one relay this is a no no. Say your fans short and go straight to ground and you have a 50amp fuse on the one circuit the fuse may not blow than you will have a wire fire. You can get relays for dirt cheap it is not worth the risk.

That's the whole point of running proper sized fuses to each item. Just like you would with any relay. You ever had a bad relay, one that would cut out when hot but work when cold. Or just one that cuts in and out due to a weak coil. Or how about the worst, they hang in when you kill the switch. So many possibilities for failure. Have seen every one of those scenarios. Its not worth the chance to me. I want to know when I flip that switch its on or off. Too many connections. Plus how do you connect them. Butt connectors. More noise, resistance and possibility for failure. I soldier and heat shrink everything only. What is the biggest problem in the pits. Electrical. Nothing is perfect but I have found this is the least way to having any problems.
this is no different than a switch burning out. Relays are designed to handle loads switch are designed to turn on relays. Yes a switch is rated at 10amps, but making a switch at full load will burn the switch out quickly where the relay is made to be cycled 10ís of thousands of times. Donít risk fires in a your car just for the sake of saving 10-50 bucks in doing it the right way. Have you ever seen a car manufacturer run the power of a pump, fan, head lights though the switch, NO. Switches are for relays and light loads, relays are for real loads, pumps, fans, lights.
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Old 10-14-2018, 09:19 AM
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You guys are going off on a bit of a tangent.

Most cars have at a minimum a "horn relay" that switches the power for all the switched loads. From there they can have either relays or switches to control the individual loads. This keeps from having the ignition switch interrupt the 30 amps or so needed to run all the accessories on a carb'd vehicle vs maybe 100 amps or so for a fuel injected one.

Switches can be rated for current interrupting or not, just like relays. House breakers are the same way. So no, a switch rated to some specific current is no more likely to burn out than a relay. One advantage of relays over switches is they can be mounted anywhere thereby reducing the length of high current wire needed. Switches in the dash means routing high current wire from the fuse box to the switch to the load.

My 1970 Datsun has one main relay to power all the loads when the ignition is on (headlights, blinkers, ignition etc). Power from this relay routes back to the fuse box, though separate fuses for each load, than through a combination switch on the column to turn things on and off. No other relays except the one main relay. After 50 years of use the contacts in the combination switch tend to corrode, partly due to arcing from interrupting current but also due to normal oxidation. This causes a voltage drop through the switch resulting in things like dim headlights. Since combination switches for a 50 year old Datsun are pricey, it is a pretty common mod to add external relays to take the load out of the switch and restore the headlights to full brightness. The dash lights do the same thing.

A switch panel would in my opinion be more reliable than relays if for no other reason than less parts and connections to go bad. But not everyone wants a race car light switch panel. Thus relays augmenting the column switches.

By the way, it is pretty common for old cars to not want to start when hot. Heat soak. A common fix is to install a Ford solenoid on the fender. What this actually does is bypasses the voltage drop through the ignition switch (and numerous wiring connectors) by routing the S terminal current through the relay instead. This applies full voltage to the solenoid allowing it to engage more forcefully even when hot. People always use that big *** Ford starter relays for this, but they could just as easily get away with a standard Bosch style relay.

I will also add I have a 25 amp fuse on my Taurus fan that only runs on low speed. I'm sure the high speed setting would blow that, but fortunately the car only needs the slow. The current draw from an electric motor increases greatly if the supply voltage is low. Thus minimizing the number of connectors and wire lengths feeding the fan will in turn reduce the voltage drop allowing a smaller fuse. Being a thermal device fuses have a bit of natural time delay, thus in rush current over the rated amperage may not blow the fuse if it doesn't last too long.
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Old 10-15-2018, 04:11 PM
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Originally Posted by Pop N Wood View Post
You guys are going off on a bit of a tangent.


Switches can be rated for current interrupting or not, just like relays. House breakers are the same way. So no, a switch rated to some specific current is no more likely to burn out than a relay.
(Exactly)

One advantage of relays over switches is they can be mounted anywhere thereby reducing the length of high current wire needed. Switches in the dash means routing high current wire from the fuse box to the switch to the load.
(You still have to run your current wires to the relays. Then there is still a switch to turn the relay off and on.)

My 1970 Datsun has one main relay to power all the loads when the ignition is on (headlights, blinkers, ignition etc). Power from this relay routes back to the fuse box, though separate fuses for each load, than through a combination switch on the column to turn things on and off. No other relays except the one main relay. After 50 years of use the contacts in the combination switch tend to corrode, partly due to arcing from interrupting current but also due to normal oxidation. This causes a voltage drop through the switch resulting in things like dim headlights. Since combination switches for a 50 year old Datsun are pricey, it is a pretty common mod to add external relays to take the load out of the switch and restore the headlights to full brightness. The dash lights do the same thing.
(Perfect example of bad coils)

A switch panel would in my opinion be more reliable than relays if for no other reason than less parts and connections to go bad.
(All I have been saying from the begining).

But not everyone wants a race car light switch panel.
(It was just an example nothing more but you still need switches regaurdless).

Thus relays augmenting the column switches.
(That is why it's a pita to find a problem).

By the way, it is pretty common for old cars to not want to start when hot. Heat soak. A common fix is to install a Ford solenoid on the fender. What this actually does is bypasses the voltage drop through the ignition switch (and numerous wiring connectors) by routing the S terminal current through the relay instead. This applies full voltage to the solenoid allowing it to engage more forcefully even when hot. People always use that big *** Ford starter relays for this, but they could just as easily get away with a standard Bosch style relay.
(Another perfect example of bad coils).

I will also add I have a 25 amp fuse on my Taurus fan that only runs on low speed. I'm sure the high speed setting would blow that, but fortunately the car only needs the slow. The current draw from an electric motor increases greatly if the supply voltage is low. Thus minimizing the number of connectors and wire lengths feeding the fan will in turn reduce the voltage drop allowing a smaller fuse. Being a thermal device fuses have a bit of natural time delay, thus in rush current over the rated amperage may not blow the fuse if it doesn't last too long.
(True but not in our case. We use aftermarket low amp fans for this exact reason. Driving around on the Street would have blown any fuse for sure. That's why you have to pay attention to amps).

This is just the way I do it and the reasoning behind it. Not saying anyone has to do it that way. Just a suggestion that's all. Do it however makes anyone happy. And we can agree to disagree.
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Old 10-15-2018, 04:14 PM
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A switch panel where switches carry the load is about the most simple setup you could get....no harm in that really.

But it does mean more, and heavier wires around the car, and also more live wires around the car.

Using relays allows you to shorten the path any heavy current needs to move, which can reduce the volume of heavier gauge wiring in the car, and relay operation can all be ground triggered, which again, is safer with less live wires all over the car.

And of course if there is an ecu etc involved....relays are almost a necessity in most cases.
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