relay wiring help
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Elder User
Joined: Jul 2012
Posts: 575
Likes: 1
From: Eastern KS
relay wiring help
alright guys, workin on the dang ram 3500... 
and i'd rather to talk to my excursion pals than the dodge people
Im needing to add a relay, however, i need to strap the coil of it with a diode to protect the friggin cluster (the new dodges arent very mod friendly!). My question is, should I add a second diode before the relay to help protect the cluster against back emf, or will the one strapped across the relay coil be enough?
Since im sure you're curious now, the cargo light (light that lights up the bed) gets its power from the gauge cluster of all places.
I need to add a relay to the cargo light circuit to drive some other lights, and im worried the back emf from the relay coil will fry the cluster circuitry.
and i'd rather to talk to my excursion pals than the dodge peopleIm needing to add a relay, however, i need to strap the coil of it with a diode to protect the friggin cluster (the new dodges arent very mod friendly!). My question is, should I add a second diode before the relay to help protect the cluster against back emf, or will the one strapped across the relay coil be enough?
Since im sure you're curious now, the cargo light (light that lights up the bed) gets its power from the gauge cluster of all places.
I need to add a relay to the cargo light circuit to drive some other lights, and im worried the back emf from the relay coil will fry the cluster circuitry.
Fleet Mechanic
Joined: Sep 2002
Posts: 1,388
Likes: 2
From: Greensboro, NC
A diode keeps electricity flowing in only one direction - it will not filter out electrical noise of any kind. I would tap the power directly from the dome light fixture for the turn on to the relay. Between the fixture and the relay add the diode so the power can only flow to the relay and not back into the light fixture.
So:
pin 86 will be the turn on from the light
pin 87 will be the 12v source
pin 85 will go to a ground
pin 30 will be the power output to the lights
For pin 87 make sure you add a fuse to that circuit as close to where you are drawing power from as possible. For pin 30 you will want a fuse between the relay and the lights and again - close to the relay.
Hope this helps.
So:
pin 86 will be the turn on from the light
pin 87 will be the 12v source
pin 85 will go to a ground
pin 30 will be the power output to the lights
For pin 87 make sure you add a fuse to that circuit as close to where you are drawing power from as possible. For pin 30 you will want a fuse between the relay and the lights and again - close to the relay.
Hope this helps.
Thread Starter
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Elder User
Joined: Jul 2012
Posts: 575
Likes: 1
From: Eastern KS
Alright thanks! Im going to go ahead and add the diode in parallel with the coil for the spike suppression, and then add a diode before the coil as you suggested to provide a second layer of protection. I'll be using the 1N4004 diode across the coil, and I think it should work for going before the relay as well.
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