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Discussion Starter #1
Advice please - I am trying to add daytime running lights module & need to find an ignition switched power source near the voltage regulator & horn relay. My car is 67 RS Convertible - original voltage regulator, original alternator upgraded by rebuilder to output 85 Amps. With an ignition power, I can add a relay to supply the power necessary to run the DRL module.

Is there any ignition switched power at the RS headlight relays?

I've converted to a Pertronics ignition & run fresh ignition power thru the firewall so wondered if I can access the former points supply near the windshield washer motor? Finding an orange, purple & a white braided wires in the harness. Was the ignition supplied through a resistor braid coated wire from the firewall connector? When converting to electronic ignition, I just wrapped the old points supply inside the harness.

Thanks for advice.
 

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It's not close to the bus bar, but you can fire the relay off the windshield wiper motor feed. I used to use it for my electric choke. You could run it inside the wiring harness on the fender well down to the front of the car.

Any relays I put on the car I like to solder a diode across the coil to quench the inductive kickback. Not an issue most of the time but I do have some newer electronics on it now. A 1N4001 or 1N4002 from Radio Shack works fine. If the relay you have says it is polarity sensitive then it should already have a suppression circuit in it.
 

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Thanks Steiner. The ww power feed will do the trick. A little more info on the diode wiring in to a relay please? I'm thinking that it goes between 86 & 85 - the control circuit. Do I just splice the diode in to the wires? Current flow from power to ground side - I assume the diode is directional? I should understand this stuff - just passed my amateur radio HAM license, but inductance was a mystery. An example of inductance in the text was an auto relay. I probably should put the diodes in place - have a relay to power hidden antenna, the DRL & a couple for more power flow to Cibie headlights.
Wilson
 

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When you get the diode, it'll have a silver band on one end. That is the cathode. You want that side on whichever relay tab you are connecting 12V. The other side goes to the tab you are connecting to ground. What I do is use a very small drill bit and make a hole in the tabs right at the relay body, run the diode leads through the holes, and solder. Then you can still get the female spade connectors on.

When the 12V is dropped from the relay, the magnetic field in the coil collapses and causes a reverse voltage spike or inductive kick back that can reach up to a couple hundred volts in some cases. The diode will suppress this kickback by shunting it to ground once a threshold voltage is reached to keep it from being fed back.
 

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When you get the diode, it'll have a silver band on one end. That is the cathode. You want that side on whichever relay tab you are connecting 12V. The other side goes to the tab you are connecting to ground. What I do is use a very small drill bit and make a hole in the tabs right at the relay body, run the diode leads through the holes, and solder. Then you can still get the female spade connectors on.

When the 12V is dropped from the relay, the magnetic field in the coil collapses and causes a reverse voltage spike or inductive kick back that can reach up to a couple hundred volts in some cases. The diode will suppress this kickback by shunting it to ground once a threshold voltage is reached to keep it from being fed back.
.....which would be the leg of the relay that is "switched 12 volts" not the control voltage leg which is always live.....correct???? I'm going to add the diode to my fuel pump relay and I want to make sure I install it correctly.

David F.
www.firstgens.com
 

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.....which would be the leg of the relay that is "switched 12 volts" not the control voltage leg which is always live.....correct???? I'm going to add the diode to my fuel pump relay and I want to make sure I install it correctly.

David F.
www.firstgens.com

Correct. The 12V connection on the coil, not the contacts.
 

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Discussion Starter #8
Steiner & David - now I'm mixed up about which relay terminals to jumper with the diode. Here's what I understand. The control power goes to 86 & 85 is grounded. Power to be used by the load is fed in to 30 & out on 87. Inside the relay, the coil is wired in the 86 to 85 circuit. the 30 to 87 circuit is just contacts that are closed when power is flowing in the 86 - 85 circuit - so there is no place for the inductance to form. It can only form in the 86-85 circuit through the coil? So that's the circuit to relieve with he diode? Does the diode carry some current whenever the control voltage is 12V?
Thanks
 

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When you get the diode, it'll have a silver band on one end. That is the cathode. You want that side on whichever relay tab you are connecting 12V. The other side goes to the tab you are connecting to ground. What I do is use a very small drill bit and make a hole in the tabs right at the relay body, run the diode leads through the holes, and solder. Then you can still get the female spade connectors on.

When the 12V is dropped from the relay, the magnetic field in the coil collapses and causes a reverse voltage spike or inductive kick back that can reach up to a couple hundred volts in some cases. The diode will suppress this kickback by shunting it to ground once a threshold voltage is reached to keep it from being fed back.
.....which would be the leg of the relay that is "switched 12 volts" not the control voltage leg which is always live.....correct???? I'm going to add the diode to my fuel pump relay and I want to make sure I install it correctly.

David F.
www.firstgens.com
Correct. The 12V connection on the coil, not the contacts.
Steiner & David - now I'm mixed up about which relay terminals to jumper with the diode. Here's what I understand. The control power goes to 86 & 85 is grounded. Power to be used by the load is fed in to 30 & out on 87. Inside the relay, the coil is wired in the 86 to 85 circuit. the 30 to 87 circuit is just contacts that are closed when power is flowing in the 86 - 85 circuit - so there is no place for the inductance to form. It can only form in the 86-85 circuit through the coil? So that's the circuit to relieve with he diode? Does the diode carry some current whenever the control voltage is 12V?
Thanks
I've read & re-read the above posts to the point that I was confused by them, so to clarify them I used the diagram below & "added" where I believe the diode should be placed. Is the diode connected to the proper terminals in the illustration below????



David F.
www.firstgens.com
 

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Yes, that's correct David. The cathode (end with the stripe) will be on terminal 86 in your diagram.


Wilson, when installed like David shows the diode will not conduct until the voltage reaches a certain level, around 50V for a 1N4001. However, if you installed it backwards it would conduct straight to ground and act like a dead short.
 

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Yes, that's correct David. The cathode (end with the stripe) will be on terminal 86 in your diagram.


Wilson, when installed like David shows the diode will not conduct until the voltage reaches a certain level, around 50V for a 1N4001. However, if you installed it backwards it would conduct straight to ground and act like a dead short.
Thanks for the "fact checking" Steiner :beers:. Now where's my drill & drill bit assortment....hmm.....my work shop. Now if I can only remember where I stashed the soldering iron :confused:.

David F.
www.firstgens.com
 

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Thanks for the "fact checking" Steiner :beers:. Now where's my drill & drill bit assortment....hmm.....my work shop. Now if I can only remember where I stashed the soldering iron :confused:.

David F.
www.firstgens.com

You bet. Now putting your tools where you can find them is one thing I can't help with. I about pop a vessel every time I work on mine.
 

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Discussion Starter #13
Thanks Steiner & David. My limited understanding of electronics was mixing me up. In some Googleing, I found a great description page here: http://www.bcae1.com/relays.htm that explains things with pictures like David's. I put a diode in a relay under the dash so I could get things hung up. Today, I stopped at an electronics supply store & bought a batch of diodes to use in the rest of my planned relays. Sure don't want to kill the new Autosound radio. Now some more soldering to do.
 
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