Regarding checking points resistance

[vdavidoff]

First, thanks in advance to everyone again for continually providing me with great information.

There's something I don't understand about checking points resistance, and I'd really like to understand it. I'll get right to it:

I am under the impression that there's a way to hook an ohmmeter to my bike ('74 GT550) to test the points individually, so that when the point I'm testing is closed I get 0 ohms, and when the point I'm testing is open I get infinite ohms.

To the best of my understanding (which obviously isn't correct, is incomplete, or both) what I described above should be the case if I connect my negative lead to ground and my positive lead to the "inner" point (the one with the lead going to it).

When I do that, using the big ground strap for my negative lead, I do get 0 ohms when the point is closed, but when the point is open I get approximately 4.5-5ohms. I am forgetting the exact reading at the moment, but I think it's actually approximately the same reading I got when checking the primary coils, which seems like it's a clue, but maybe not. The battery is disconnected, ignition off, and run switch off when I'm doing this.

I guess what I don't understand is, with the points open, battery disconnected, and all ignition related switches "off", what is left to complete a circuit once the point opens. Right?

When I get the ohm reading above 0, this does align with the points opening visually and the timing marks, so it does seem that I'm getting the reading at the appropriate time.

So my question is, why I am not getting a reading of infinite ohms when the points I'm monitoring are open?

Thanks.
Andy

[jabcb]

The dwell angle for the GTs is something like 180°, so at least one set of points is always closed.

When the points you are checking are open, the circuit you are measuring is:
1) wire from points to coil
2) coil
3) wire from coil to other coil
4) other coil
5) wire from other coil to other points
6) other points to ground

The coil resistance is about 4 ohms.
With only one other point closed, you'll measure about: 4 + 4 = 8 ohms
With both other points closed, you'll measure about: 4 + 4/2 = 6 ohms

[tz375]

If you want to check the points on their own, they have to be disconnected. As JABCB mentioned, the points are connected to the coils, so you are actually measuring more than just one set of points on their own.

[vdavidoff]

Thank you. That totally explains it. I was missing the part where the coils are connected together.

Thanks!!!
Andy

[H2RICK]

Easy solution: Put a piece of some insulating material between the contacts of the point sets you're NOT checking.