checking voltage to coil
When checking to make sure coil is getting full 12V when key is in start position and you don't want engine to start, what's best way to disable ignition from firing without damaging coil on points type setup?-disconnecting wire to coil from distributor? just pulling coil wire out of distributor cap (if so, does coil to distributor wire need to be grounded to block to prevent coil damage?)? Thanks
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Re: checking voltage to coil
With the ignition off and the points open short the solenoid S-terminal to the solenoid battery cable stud with a jumper wire that has alligator clips. This should show 12V at the coil + terminal, but no current will flow with the points open.
Connect a jumper wire with alligator clips to the S terminal first and then the solenoid stud, and disconnect in the opposite way. This will reduce the danger of shorting the 12V to ground. Remember, that stud on the solenoid is hot when the battery cable is connected.
Alternatively, disconnect the pink wires from the + coil terminal. Crank the engine and measure voltage at both the battery and the loose coil wires terminal. They should both be the same - about 10.5 volts while cranking.
Duke -
Re: checking voltage to coil
Duke, Thanks, but you lost me on the alternative method.Actually 2 questions: 1. After I disconnect the pink wires from the coil, where do I attach the clips from my V meter to see if full12V is going to coil with key in start position? 2.Last time I suspected this problem on another car, we put V meter leads on S terminal and other one on coil and read V while turning motor over with key; don't remember if we just pulled coil to distributor wire off to keep motor from stating during test-wondering if this taking coil wire off can damage coil on a points system(I remember GM said ground coil wire on the later HEI ignitions.Comment
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Re: checking voltage to coil
Bill,
Electrical is my short suit but it would stand to reason the starter motor will inhibit the coil from full battery voltage just because it draws so much.Comment
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Re: checking voltage to coil
Bill, you should see battery voltage during cranking on start-up , just put you clip to the pink+ wire at coil and face the volt meter so you can watch it during the cranking mode. don't touch the gas pedal so it will crank a few seconds. once started the ballast will take over.New England chapter member, 63 Convert. 327/340- Chapter/Regional/national Top Flight, 72 coupe- chapter and regional Top Flight.Comment
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Re: checking voltage to coil
Gene,Wiring is such that when you turn key to start, ballast resistor is bypassed giving full 12V; takes more energy to start than run. When key goes back to run, ballast resistor is back in circuit decreasing voltage to points so they won't burn.Comment
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Re: checking voltage to coil
Where does other v meter clip go? to a ground? Does + clip go to pink terminal and _ to ground or does orientation of clips matter ? Had hard start problem with another car and did turn out to be corrosion inside solenoid not allowing full 12 V at cranking, but forgot exactly how I connected V meter for test.Comment
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Re: checking voltage to coil
Yes, the other lead goes to ground for measuring voltage.Comment
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Re: checking voltage to coil
Y'all are making this overly complicated.
You want to know that during cranking the ballast resistor is being bypassed. Simple. Connect your Volt meter directly across the two ballast resistor terminals and crank the engine.
During cranking the meter will (or should) read zero Volts. When the engine starts and you release the key, the meter will indicate several Volts.
Simple. Easy to remember.
JimComment
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Re: checking voltage to coil
Jim that's not what I'm asking. I'm trying to find out if full 12V is getting from solenoid to coil/points when key is turned to start. Corrosion inside solenoid can decrease voltage going from it. Just want clear instructions on how to hook up V meter to test. Know I can put one lead directly on S terminal of solenoid and other on coil but this requires getting under car for solenoid connection.Comment
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Re: checking voltage to coil
Understood. My best advice, then, is to simply measure the Voltage at the coil while cranking. You'll see full cranking Voltage, ~11 Volts or so, if the ballast resistor bypass is working and that will drop to something between ~5 and ~7 Volts when the engine starts and you release the key.
This is a very simple problem. Don't over think it.
JimComment
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