Stock Ignition Coil Resistor

[stanz]

Yes. The "S" on the voltage regulator (Green w/red wire) is 12v with the key in the ON position only.

Paul

Thanks again Paul! My VR harness has almost all entirely yellow wires (firewall mounted) but I understand that the S terminal is the third in from the left - IASF

 

[DirtDonk]

Yep, looks like the colors have fallen prey to the ravages of time.
You can just barely see the Orange and Green hues to the others still.

But you're on track. And one additional test that would be good to make before you commit to this as a power source, would be to measure voltage at that middle wire there at the S position. See if it's got full battery voltage, or has dropped some, which will tell you if it's still a viable power source for your ignition.

You're looking for as close to battery voltage as possible, so measure the battery first, then measure at the S wire with the key ON to see how far off it is. You want it as close as possible to the same. Less than half a volt different I would think.
Personally, if it's got near a full volt of drop, I'd be considering another source, or use it to trigger a relay like you were thinking before.
If it's full battery voltage, you're golden. If it's less than half a volt less, you're probably still safe.

Just thinking ahead here, since wiring can build up resistance over time and it's good to know the condition.

Paul

 

[stanz]

Yep, looks like the colors have fallen prey to the ravages of time.
You can just barely see the Orange and Green hues to the others still.

But you're on track. And one additional test that would be good to make before you commit to this as a power source, would be to measure voltage at that middle wire there at the S position. See if it's got full battery voltage, or has dropped some, which will tell you if it's still a viable power source for your ignition.

You're looking for as close to battery voltage as possible, so measure the battery first, then measure at the S wire with the key ON to see how far off it is. You want it as close as possible to the same. Less than half a volt different I would think.
Personally, if it's got near a full volt of drop, I'd be considering another source, or use it to trigger a relay like you were thinking before.
If it's full battery voltage, you're golden. If it's less than half a volt less, you're probably still safe.

Just thinking ahead here, since wiring can build up resistance over time and it's good to know the condition.

Paul

The more I think about it, the more I like the relay idea... provides protection against overloading the circuit and I can run a clean fresh wire with an inline fuse to the coil. Can’t thank you enough Paul for your assistance!

 

[DirtDonk]

The only thing I don't like about adding a relay is you're adding another potential failure point. But the benefits are obvious and important as well.

So much is done on relays these days that if you are able to purchase "good" relays (whatever that means!) they should last a long, trouble-free time.
Hella brand are often made in the USA or Germany or Austria, which to me still bodes well for their quality.
Or if you are able to source the weatherproof kind, they're usually more expensive, but of apparently good quality too from what I've seen.

Paul

 

[Steve83]

...the S terminal is the third in from the left...

The connector pinout is shown in the diagram I posted before.

 

[stanz]

Thanks @steve83. That diagram is very helpful!!

I guess going back to my opening question, is there any harm in using the coil wire (post firewall) to trigger a relay to run 12v to the new coil?

 

[Steve83]

Not if the voltage is high enough to trigger the relay you use.

But it's extra work when you can simply use the VR Gn/R wire to directly power a 12V coil.