Continuity Across Distributor Point

R

RonLey

Member
I need some other ideas as I am out. My 28 Roadster started running rough above idle. Went through all of the normal checks. I finally decided to check the points gap and then check timing. The issue is that when I put my ohm meter across the points I get continuity whether the points are closed or open. I have checked the lower plate and pigtail, checked that no loose rivets etc.

I am sure that someone else has had this happen. I tried the search but didn't find a thread.

Ideas?
 
If the key is off on an original popout the movable points arm is grounded, so you can't do an ohm test.

I like to use a test light and follow the voltage with the points open and closed when the key is on.
 
Tom Wesenberg said:
If the key is off on an original popout the movable points arm is grounded, so you can't do an ohm test.

I like to use a test light and follow the voltage with the points open and closed when the key is on.
Click to expand...

Yet another reason to use a test light that actually draws power (current) instead of a meter that simply determines the presence or otherwise of a voltage. (Yes, I know this is a test for resistance not voltage, but the notion is still applicable.)
 
Last edited:
Tom Wesenberg said:
If the key is off on an original popout the movable points arm is grounded, so you can't do an ohm test.

I like to use a test light and follow the voltage with the points open and closed when the key is on.
Click to expand...

Here is a picture of what Tom is talking about. When pushed in, the wire to the points is shorted to ground.
 

Attachments

  • pop out switch.jpg
    pop out switch.jpg
    54.8 KB · Views: 5
Another thing that happens some times, is when you screw the ignition cable into the distributor, it pushes the lower plate in contact with the distributor body and creates a short. You can insulate the back side of the lower flange to prevent that from happening. Also be sure the point nut/ wire is not contacting the spring under the lower plate, or touching the side of the distributor.
 
This last week I had a similar issue. I was using the modern points. I had several spare distributors, two totally new rebuilts and an old one. the newly rebuilts were also using the modern points. The points were showing continuity both open and closed. We removed the points from the distributor and they still showed continuity when just held in the hand. The old distributor, old point set-up was the saving factor in getting home.... about 200 miles!
 
Also watch the points straps, both the spring and current carrying, as I've seen them touch the distributor cam, especially if the rubbing block gets worn too short.
 
I have seen modern points with an internal short in the area where the black wire attaches. They depend on those little insulators to keep things apart. Very cruel thing to happen. Hard to find.
 
You must log in or register to reply here.
Back
Top