Posted by Clint Dixon [104.22.62.40] on Saturday, September 26, 2026 at 10:04:58 :
In Reply to: Re: Electrical Issue - Paging Tom Petroff posted by Tom Petroff (IL) [172.69.59.25] on Friday, September 25, 2026 at 20:28:26 :
Thanks Tom. To quote you:
"Sounds like a shorted coil and can happen slowly over time.
Do a ohm test by removing + & - wires from the primary terminals. Set ohm meter lowest setting probably 200 ohm setting. The reading between the + & - terminal should be around 1.5 ohms to 2.0 ohms.
Next set vom meter to 20,000 ohms and test the secondary winding by probing the tower to either the + or - terminal. Should be between 6k to 12k ohm range."
Here is what I found:
On the '47 that is starting and running good I get 3.2 ohms across the '+' & '-' terminals. I then get from the tower - 6.62 ohms to both the '+' & '-' terminals. All with three tests agreeing
On the '51 that is having the trouble I get anywhere from 1.3 to 2.6 ohms across the '+' & '-' terminals with multiple tests not agreeing. I then get from the tower - 6.31 to 6.62 ohms on the '+' terminal and 6.32 ohms on the '-' terminal.
I cannot put the coil from the '47 and put on the '51 to see if it makes it start and run better as they changed coils and mounting brackets between those years and it would not be a quick job to switch everything over and back again.
I did test two old spare nasty coils I have in my "junk" pile just for reference. I got 4.4 / 6.36 / 6.36 ohms on one and 2.0 / 3.53 / 3.52 on the other. Both listed in same order as my results on the '47 and '51.
In answer to Keith. I tested and found no grounding at the coil-to-distributor terminal on the side of the distributor.
I would try another condenser, as I have no way I know of to test them, but modern condensers (what I have collected over the past 30 or so years) do not want to fit in the small '51 B3PW distributor housing without rubbing on the spinning distributor shaft once screwed in place.
On old NOS condensers I have to file open the wires lug to fit the stud that the points also connect to. These are number correct condensers so maybe the stud and the internal insulation parts are not original to the distributor? The tag on the dist indicates that it is correct to the truck but it could have been altered at one time or another.
So do my findings still point to a bad coil?
Junior
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