points ignition & resistance wire
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points ignition & resistance wire
first off- i'm no electrician, but i'm okay with a voltmeter.
scratching my head on this one.
1965, points ignition (triggering a TFI ignition module, but i'm not sure that matters here)
i can see the resistance wire under the dash. it disappears into the harness, and i don't see any evidence of it being bypassed before it hits the firewall.
but- with the points closed, i'm getting 12v at the coil +.
i pulled the wire off the coil, and measured resistance from there to the key switch- 2 ohms.
how could the wire be showing 2 ohms, but i'm still getting 12v at the coil?
scratching my head on this one.
1965, points ignition (triggering a TFI ignition module, but i'm not sure that matters here)
i can see the resistance wire under the dash. it disappears into the harness, and i don't see any evidence of it being bypassed before it hits the firewall.
but- with the points closed, i'm getting 12v at the coil +.
i pulled the wire off the coil, and measured resistance from there to the key switch- 2 ohms.
how could the wire be showing 2 ohms, but i'm still getting 12v at the coil?
Cargo Master
Joined: Mar 2008
Posts: 2,573
Likes: 207
From: Washington
first off- i'm no electrician, but i'm okay with a voltmeter.
scratching my head on this one.
1965, points ignition (triggering a TFI ignition module, but i'm not sure that matters here)
i can see the resistance wire under the dash. it disappears into the harness, and i don't see any evidence of it being bypassed before it hits the firewall.
but- with the points closed, i'm getting 12v at the coil +.
i pulled the wire off the coil, and measured resistance from there to the key switch- 2 ohms.
how could the wire be showing 2 ohms, but i'm still getting 12v at the coil?
scratching my head on this one.
1965, points ignition (triggering a TFI ignition module, but i'm not sure that matters here)
i can see the resistance wire under the dash. it disappears into the harness, and i don't see any evidence of it being bypassed before it hits the firewall.
but- with the points closed, i'm getting 12v at the coil +.
i pulled the wire off the coil, and measured resistance from there to the key switch- 2 ohms.
how could the wire be showing 2 ohms, but i'm still getting 12v at the coil?
Jim
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Joined: Jan 2001
Posts: 56,990
Likes: 2,740
From: Virginia
Yes, if you have the coil + resistance wire just hanging out in the air not hooked to anything, and are reading it with your voltmeter like that, then you will get 12v because there is no current flow. There is a little bit of current flow caused by your meter, but it's not enough to cause the proper voltage drop through the resistor. Like Jim said, make sure you hook the coil up, and current is flowing through it to properly load the circuit, and then take a reading. You can do it like he said, or you can just get the engine running and take a reading at the coil + with the engine running.
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thanks guys-
the project i'm working on is putting in an E-core coil (to match the TFI ignition module i'm already using). Since that coil can handle 12v, I got impatient and just bypassed the resistance wire last night.
here's what i *think* was messing up my readings:
even though i was checking with the points closed- my points aren't wired directly to coil -. they're wired to the TFI module. the TFI module has a separate wire that goes to coil -.
i'm assuming now that closing the points doesn't necessarily mean that the TFI module is allowing current to flow through the coil.
if that's the case, the suggestion to ground the coil or simply check with the engine running, would have been spot on.
thanks to both for your replies...now i wish i'd waited to bypass the resistance wire so that i'd know for sure why my readings were weird.
the project i'm working on is putting in an E-core coil (to match the TFI ignition module i'm already using). Since that coil can handle 12v, I got impatient and just bypassed the resistance wire last night.
here's what i *think* was messing up my readings:
even though i was checking with the points closed- my points aren't wired directly to coil -. they're wired to the TFI module. the TFI module has a separate wire that goes to coil -.
i'm assuming now that closing the points doesn't necessarily mean that the TFI module is allowing current to flow through the coil.
if that's the case, the suggestion to ground the coil or simply check with the engine running, would have been spot on.
thanks to both for your replies...now i wish i'd waited to bypass the resistance wire so that i'd know for sure why my readings were weird.
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