Testing coil

[Dwmadsen]

1981 R65 with single coil/dual tower.
Re testing coil: Manual says to test voltage between terminal 15 and ground. I get no voltage at terminal 15. I get 12.5v  from the cable which connects to terminal 15. Before I buy a new coil, I want to ensure I am testing correctly. One of my questions is with terminal 15 disconnected (to perform the voltage test), from where would the coil be getting its voltage?

[Bob_Roller]

First, why do you suspect the coil is faulty ?
You stated that you get battery voltage from the black wire that goes on the coil .
If I understand you correctly you are looking for voltage at the terminal in the coil with the wire disconnected,if that’s the case. You will not get a voltage reading at the terminal
better way to check the coil, is to do a resistance check between the two outputs from the coil, remove the spark plug leads and check for resistance between them ,
Should be around 11-13 k ohms ,
Thats the check for the secondary coil circuit .
To check the primary circuit, check the resistance between the two terminals that the black and I think green and black wires go .
Should have a reading of about 1.5 ohms .
Is the coil black and gray, or black and red or an aftermarket coil .
What color spark do you get when you remove the spark plugs and still have the leads on them set them on the cylinder fins and operate the starter ?

[Dwmadsen]

Bob,
Thanks for your detailed response. I have been resurrecting the bike and am at the point of putting it on the road. The bike has started and idled fine; I have yet to button it up and go for a ride. Then a couple of days ago I attempted to start it and found myself in a no spark condition. I do not remember the condition of the spark when I initially prepared to start the bike. The bike - until now - has started without issue.

I have troubleshot the wiring, grounds, connectors from battery, ignition, brake, kill, neutral, and oil pressure switches. I got to the coil and was following the procedure in the Clymer’s manual - which brings me to my original post.

Following your guidelines, there is 12.44k Ohms resistance between the HT terminals. There is 0.5 Ohms between terminals 1 and 15. The coil is an OEM 0221500203 (red) and has no apparent cracks or damage.

The PO(s) seemed to have kept the bike stock (no mods) and items like the HT rubber boots are in excellent condition with the inside of the boots treated with dielectric grease. I mention this last part to indicate the bike has not appeared to have been sitting behind a barn for years🙂.

Dave