Weird meter readings when checking the coil on a WD-45?

Will Herring

Well-known Member
Working on a friend's WD-45... Has a 6V system with a generator, distributor, coil, etc. Battery is sitting at about 5.5V. I turn the key switch on, and use my meter to measure voltage at the coil (the coil ohmed out okay... somewhere between 1.5 and 3.0 ohms, I think). I'm seeing the voltage fluctuate between 2.4V and 4.5V, just back and forth, back and forth. The tractor will "crank over", but this voltage reading puzzles me. I need to drain the gas tank and flush out the carb, but makes me wonder if something weird electrically may be going on too.
 
Points are very likely to be closed and not working well so you are getting an up down reading due the the points making and breaking so they need to be cleaned and or replaced
 
Hmmm... Will try to clean the points first to give it a shot and check again. I thought maybe the condensor was shorting out, but didn't think about the points. This tractor has sat for about 8 years without running, so I can believe there's all sorts of gremlins. Will open up the cap and see what I find. I probably ought to pull a plug and make sure all of the wires will give me spark after that too, I presume?

Also old -- I finally put that hub cap from your parts tractor on my WD last weekend when I rebuilt my front end to replace the one that was damaged. Looks good and thanks again!

cIzPUt6.jpg
 
Id bet contac area on point face has white
oxydation on them,piece of fine sandpaper folded
and ran between contacs can cure lots,check gap
 
Put your volt meter from the distributor side of the coil to ground.

Turn the engine until the points are closed.

With the ignition on, should get 0 volts. If any voltage, the points are not making good connection.

Now, if the reading is at 0 volts, move the test lead to the ignition switch side of the coil.

Should get steady near battery voltage. If considerably lower or still fluctuating, look foe a bad ignition switch or a bad connection somewhere between the coil and the switch or the switch and the battery.

Just don't leave the switch on and the points closed too long, it will overheat the coil.

Also, the battery at 5.5v with no load is not fully charged. Slow charge it until it reads around 6.4v off the charger.
 
Points open you should read battery voltage at the ignition side of the coil. If points are good you should read very little voltage at the ignition side of to coil when closed
 
Will, a full charged 6 volt lead acid battery at rest and stabilized should read around 6.3 volts, if its actually 5.5 its pretty low and such could cause low or erratic voltages.

If the battery is okay and the ignition switch is good (no resistive contacts) and ON when the points are open a meter on the coils input would read near same as voltage at battery and likewise even when they are closed. If voltage on coils input drops drastically below battery voltage when key is on and on and points are closed there may be a faulty resistive ignition switch. TRY TO HOT WIRE DIRECT FROM BATTERY TO COILS INPUT in case the switch is bad

Now put a volt meter over on the coils output to distributor terminal and turn the key on. When points are open it should read near battery voltage but when closed it should read near zero. If the engine were cranked slowly a test lamp there should flash ON (points open) and OFF (points closed).

I would check the points and remove any oxidation or carbon and insure they are clean, not all burned and pitted, maybe use a points file to lightly dress them up better yet if burned or pitted or carboned bad get a new set.

If the condenser,,,,,,,,, or its wiring,,,,,,,,,,, or wiring from coil to and thru distributors pass thru were shorted voltage on the coils output would read near zero all the time regardless if points open or closed.

Check points for burning or carbon or oxide or pitting, check voltage on coils in and out with points open and closed,,,,,,,,,,check battery voltage.

If this fails work through my detailed Ignition troubleshooting Procedure to find the problem but its sooooooooooo often bad points or not gapped correct and not opening and closing fully

John T
John Ts Ignition Troubleshooting
 
OK, just to be clear, you are measuring the voltage from the DISTRIBUTOR side of the coil to GROUND, right? And you are making this measurement with the ignition on, engine stopped and NOT CRANKING.

If that is the case, and everything else is in order, you should see EITHER 1) battery voltage (points are open); or 2) less than one volt (points are closed), ideally less than a tenth of a volt with new points.

It sounds like you have seriously burned points.

Now, if you're trying to measure the voltage across the points with the engine running, then it's anybody's guess what you'll see. Assuming you're using a digital multimeter, most DMMs have a hard time locking on to rapidly changing voltages. You really need an oscilloscope to look at the point voltage on a running engine.
 
Okay, will go back next time (hopefully this weekend) and check some more of the electrical system. I indeed was measuring it with the key on while *not* cranking. Pretty sure I was on the distributor side, but will verify that next time as well. Will pop covers and take pictures and maybe clean up inside.

Any easy way to tell if the switch is bad?

Thanks for the ignition troubleshooting checklist John T.

Will report back again when I know more.
 
If you are reading any significant voltage across the points with the points CLOSED, then the points are bad. Whether the switch is bad or not.

If you are reading less than battery voltage across the points with the points OPEN, then something is seriously wrong besides the points. Backtrack the current path from the distributor to the battery. Wherever the voltage (referenced to ground) jumps up to battery voltage, that's where your problem is. For example, if one side of the ignition switch has six volts and the other side has four volts, then the switch is bad.
 

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