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Relay wiring help?

dodge68charger

dodge68charger

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Hey Guys,

Looking to wire up some accessories in my 68 charger. Led lights, fans, etc.

I was told to run relays. Just wondering how wire a relay properly to the load? I’d like to use LED Switches so I know when the accessories is on.

Is there a certain numbered terminal on the relay I put the swich on. Gonna use a 12v ign source for my smaller trigger wire

Just looking for a simple diagram. Thanks
 
Speaking of 4 pin relays; Pins 85 and 86 are the control side. Either can be hot or ground. 87 and 30 are the output. Again using either side. However I always use pin 30 attached to the hot feed (see below in 5 pin relay discription for this resoning.). Attach the LED hot to whichever output terminal is feeding the device. Then it will illuminate when the relay is on. 5 pin relays have an additional pin, 87A. This pin has continuity to pin 30 when the relay isn't energized. When it is energized 30 and 87 have continuity and 87A is open circuit.
Doug
 
Most relays come with a diagram. If not, Google it !! Whether you use four or 5 pin relays is neither here nor there - they all work the same.
 
You want to keep the system fused. So use either an inline fuse or cct breaker for each relay. Pick either 30 or 87 as the hot terminal & connect to the alt post. Wire the fuse/cct breaker inline between the alt stud & terminal 30/87.
 
Led lights won’t really need relays. Fan does thought.

I can post a diagram I have made as a suggestion to make work a dual fan system with an automatic temp sensor switch, without using a control module system. And using an override switch with a light which works as a pilot light knowing when is activated (either by the switch or by the temp sensor switch)

As mentioned, tipically 30 is input hot (either positive or negative if is handled by a negative source ), 86 ground, 85 trigger from switch and 87 the output to the device to be switched on

87A on 5 prongs relay Is the extra prong for a dual on system, (I.e. hidden headlights system) what as mentioned keeps a closed circuit with 30 post while trigger is off
 
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This is my suggestion.

Dual fan system with a secondary fan which will work as soon it gets the second temp range (per your own temp sensor selected range) AND ALSO when you turn on the A/C. Also the second fan will be turned on by the override switch on dash in case of emergency.

Of course the light on lighted switch will be turned on just when the second fan is on. That will tell you your AC is working, you reached the second temp range stage, or you turned on the override switch itself. Except if adding a diode (as explained on legend)

Can be used also for dual speed single fan, just need to be sure about what to wire on every speed input on fan.



dual%20fan%20option%20FULL.jpg
 
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dvw said:
Speaking of 4 pin relays; Pins 85 and 86 are the control side. Either can be hot or ground. 87 and 30 are the output.
Click to expand...
Not totally correcr, it depends on the type relay. Bassically 3 different types.
Basic= it makes no difference
resistor damped= makes no difference
Diode damped= polarity makes a difference. If hooked up the wrong way the relay will act as a dead short in the trigger circuit
Offhand I don't remember which terminal is neg and which is pos. I need to look it up.

EDIT: with a diode damped relay terminal 86 is positive, and terminal 85 is neg. If you wire the relay terminals this way, you can use any bosch relay without any issues.

Automotive Relay Guide | 12 Volt Planet

Read our guide to relays found in vehicle electrical systems. How they work, why they're used and some example applications
www.12voltplanet.co.uk
 
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Anything you ever wanted to know about wiring up relays with tons of diagrams.. Relay Wiring Diagrams | the12volt.com Electricial is something where there is more than one way to skin a cat.

And if you want the simple way out for doing headlights, there are plenty of companies that sell pre-made harnesses that plug into your existing headlight harness and draw power directly from battery..
 
Charrlie_S said:
Not totally correcr, it depends on the type relay. Bassically 3 different types.
Basic= it makes no difference
resistor damped= makes no difference
Diode damped= polarity makes a difference. If hooked up the wrong way the relay will act as a dead short in the trigger circuit
Offhand I don't remember which terminal is neg and which is pos. I need to look it up.

EDIT: with a diode damped relay terminal 86 is positive, and terminal 85 is neg. If you wire the relay terminals this way, you can use any bosch relay without any issues.
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Click to expand...
The diode dampened relay is intriging. Great feature for fan motors to prevent flyback spike damage.
Doug
 
dvw said:
The diode dampened relay is intriging. Great feature for fan motors to prevent flyback spike damage.
Doug
Click to expand...
The damped relays are mainly used in circuits that are controlled by the vehicle computer. When the trigger circuit is activated by the computer the load is powered up. When the computer opens the trigger circuit to turn off the relay/load and back EMF is generated in the relay coil (just like an ign coil). This voltage can be several hundred volts, and can damage the computer. With a diode in the trigger circuit (across the relay coil) this back EMF is shorted out and does not reach the computer. A resister damped relay does ALMOST the same thing (dampens the back EMF) but still allows some voltage to enter the circuit. The use of the relays depends on what is controlling the relay and how sensitive it is to the high voltage. For our "older" vehicles it generally does not matter and the basice relay can be used. However if adding other non standard assories, this needs to be taken into account. Think electric fan control using a solid state controller, after market FI, etc.
 
Nacho-RT74 said:
This is my suggestion.

Dual fan system with a secondary fan which will work as soon it gets the second temp range (per your own temp sensor selected range) AND ALSO when you turn on the A/C. Also the second fan will be turned on by the override switch on dash in case of emergency.

Of course the light on lighted switch will be turned on just when the second fan is on. That will tell you your AC is working, you reached the second temp range stage, or you turned on the override switch itself. Except if adding a diode (as explained on legend)

Can be used also for dual speed single fan, just need to be sure about what to wire on every speed input on fan.



View attachment 1906455
Click to expand...
Your statement in post #6 as to the polarity of terminals 85 and 86 is incorrect. The polarity of terminals 85 and 86 in the posted diagram is correct.
Terminal #85 is negative/ground, and terminal #86 is positive, I always wire this way even if using the basic relay with no dampening. That way if for some reason I install a diode damped relay it will not cause a problem.
PS: That is a very good diagram.
 
Charrlie_S said:
The damped relays are mainly used in circuits that are controlled by the vehicle computer. When the trigger circuit is activated by the computer the load is powered up. When the computer opens the trigger circuit to turn off the relay/load and back EMF is generated in the relay coil (just like an ign coil). This voltage can be several hundred volts, and can damage the computer. With a diode in the trigger circuit (across the relay coil) this back EMF is shorted out and does not reach the computer. A resister damped relay does ALMOST the same thing (dampens the back EMF) but still allows some voltage to enter the circuit. The use of the relays depends on what is controlling the relay and how sensitive it is to the high voltage. For our "older" vehicles it generally does not matter and the basice relay can be used. However if adding other non standard assories, this needs to be taken into account. Think electric fan control using a solid state controller, after market FI, etc.
Click to expand...
Good explanation. I know about flyback and have seen the damage firsthand. Just never thought about (or had seen a diode relay). Had an issue last year with the alternator on my racecar. Every couple of weeks it would fail the internal regulator whch was an adjustable 12.5v-19.5v unit. Checked all wiring by voltage drop, hot and ground. Didn't see anything. Swapped regulator brands this past winter. At that time I also thought about flyback spikes. The fan relay feed came off the alternator output stud. Did it have a spike issue when the fans shut down (30 amp draw running)? Maybe? At the same time the the regulator was swapped the alternator output feed became a dedicated circuit from the output stud to battery only. No problems since. The diode relay would've been an easier solution if in fact flyback spike was the issue. Or maybe it was a poor design regulator, I'll never know.
Doug
 
dodge68charger said:
Just looking for a simple diagram. Thanks
Click to expand...
You need to first understand what a relay is.

It can be as simple as a device that has a set of contacts for passing a large current through to a device - eg. flood lights, fans, starter motor etc.

You call for a relay when the switch contacts are not designed for excessive load current or arcing from the load.

The relay contacts are designed for switching of high currents and arcing loads.

Now - once you have a relay in front of you, the 'Output' side of the load (wire going to device) will also give you the feedback for the illumination of the switch if that is what you are trying to achieve with knowing the relay is running. You will only need a small gauge wire to feed back to the switch illumination terminal. Don't forget that the switch will likely have a ground wire for the illumination to operate.
 
Charrlie_S said:
Your statement in post #6 as to the polarity of terminals 85 and 86 is incorrect. The polarity of terminals 85 and 86 in the posted diagram is correct.
Terminal #85 is negative/ground, and terminal #86 is positive, I always wire this way even if using the basic relay with no dampening. That way if for some reason I install a diode damped relay it will not cause a problem.
PS: That is a very good diagram.
Click to expand...
Sorry, A type mistake
 
No, not polarity sensitive because the diode can be connected either way.....
 
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