Voltage to coil on 39 Ford

[George/Maine]

The test with voltage should be done running.
OHMs law best place to check is across resister 1.8 but what do you get running.
.6 ohms x 3 amps = 1.8
Do a tune-up adjust points and go with new condenser.
You could have and old coil and maybe no good.

[big job]

resistors ohms and all that. Buy your self a Plymouth 6vt pos ground. go find a resistor in that?? worked on a kirillion 6vt vehicles seems Ford only one with a resistor, is it
cause of duel points? don't know. 1939 Chev no resistor; they came along in 1956
when about everybody went to 12vt neg grd. correct me 6vt with coil resistor then
push the starter now what you got lucky it starts..I run no resister no problem

[mjdunn]

I overlooked the "disconnect" note. I have to leave for an appointment now. I'll check it further in an hour or two.

[JSeery]

Big job, it has to do with the coil that is used. A flathead Ford will run fine without a ballast resistor if you use a coil that doesn't require one. There are advantages to using a ballast resistor, but an ignition system can be set up either way. Ford removed the ballast resistor in some later year 6v systems, and then with back to it with the 12v change.

[flatheadmurre]

You can disconnect the ignition coil instead if you don´t want to crawl around under the dash...the circuit just needs to be open somewhere.

[Bill OH]

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Set Ignition switch to OFF and then measure resistance across resistor. Also, clean the resistor and wire ring terminals together with running the brass nuts across a file, then put two nuts on the posts followed by the resistor and then the wire ring terminals and last put on the two bass nuts and tighten them. Now check the resistor after reinstallation and compare that value with an ohm check across the resister as it lays on your work bench.
While your at it clean the contacts in the ignition switch and use dielectric grease on the contacts. Your problem may be dirty connections, which need to be CLEAN and TIGHT.
ALSO, clean the ring terminal on the battery post on the coil.

[mjdunn]

Mac at VanPelt Sales informed me that I had an aftermarket resistor and he sent me a genuine Ford resistor. I installed it and it solved my problem. I appreciate all of the advise I received from this forum. It helped me get to the bottom of the problem.

[JSeery]

Originally Posted by mjdunn

Mac at VanPelt Sales informed me that I had an aftermarket resistor and he sent me a genuine Ford resistor. I installed it and it solved my problem. I appreciate all of the advise I received from this forum. It helped me get to the bottom of the problem.

Good feedback! Lots of reports of problems with aftermarket original style ignition resistors.

[zoegrant]

Flatjack 9 & JSeery....please explain which leads you are talking about ? Thanks

[flatjack9]

I think I stated the leads on the resistor.

[Tinker]

It's very informative when someone follows up on their questions they ask. Rare but good.

[JSeery]

Originally Posted by zoegrant

Flatjack 9 & JSeery....please explain which leads you are talking about ? Thanks

"You must disconnect the leads to the resistor to measure the resistance." Flatjack was referring to the wires that connect to the ballast resistor. That is one way to do it. What is really required is that there is only one path for the current to flow between the resistor terminals when you check resistance (ohms). Anything that isolates it will work, and as was suggest it should be fine with just the ignition switch turned off. If there is another current path anywhere it will change the reading. It would just be good practice to remove the leads (wires) on the resistor so you are positive you are measuring only the resistor. But for a quick check it probably is not that big of a concern.

[BUBBAS IGNITION]

Originally Posted by JSeery

Good feedback! Lots of reports of problems with aftermarket original style ignition resistors.

I dont think its the problem with the actual resistor , its the fact of it being a incorrect resistance value......

[JSeery]

Originally Posted by BUBBAS IGNITION

I dont think its the problem with the actual resistor , its the fact of it being a incorrect resistance value......

Ok, thanks for the input. I though it was the "bamboo" construction that was the problem. So the replacement Ballast Resistors are the incorrect resistance value?

[zoegrant]

jseery...thanks for clearing that up for me. I have another question...on a 6v system, how much voltage should there be at the coil with the engine not running but the iginition switch turned on ?

[George/Maine]

There is nothing better then changing a part and the car runs better.
But over the years here there has been more coils gone bad.
A little less resister would increase the coil amps and voltage go's up.
I like to check voltage across a known value like .5 ohms resister running.
Its like about 3 amps x .5 ohm= 1.5 volts. what's left is 1.5 from 6= 4.5 voltage. +or-

[FlatheadTed]

About 5 ,5 to 5.9 volts with the coil disconnected, Ted

Originally Posted by zoegrant

jseery...thanks for clearing that up for me. I have another question...on a 6v system, how much voltage should there be at the coil with the engine not running but the iginition switch turned on ?

[zoegrant]

With A fully charged battery and my coil wire disconnected from the distributor and the iginition switch on, I have 5.8 v going into the resistor under the dash and 3.7 coming out of the RED wire at the "coil."
Is this enough voltage to start the car ? The car has sat for 9 years and hasent been started. I have tried but to no avail. I have done the following:
Tried another coil.
All new fuel line and tank and gasoline.
New mechanical fuel pump
New in line electric pump to prime carb.
Professionally rebuilt carb.
Professionally rebuilt helmit type distributor.
New plugs and plug wires.
Complete new wire harness.
New battery.
Starter checked for resistance and checks ok.

With all this I still cannot start this engine. It does not even try to catch...What else can I try ?????

[JSeery]

Voltage into the ballast resistor should be near the battery voltage, something above 6v, say 6.3 or so (not running). Which coil are you using, an original type that mounts on the top of the distributor? What is your fully charged battery reading? What is the resistance of the ballast resistor itself? Bubba just posted about replacement resistors being an incorrect value.

If the battery is reading a little above 6v, I would run a temporary jumper wire from the battery or the hot side of the starter solenoid directly to ballast resistor. Only leave it connected for a short period of time. See what that does. The ignition switch or wiring may have excessive resistance.

If it is the round can style coil it shouldn't be using a ballast resistor and would be wired directly to the ignition switch.

[supereal]

The running voltage at the coil is pulsed by the action of the points. In order to determine the value of the reading, you need to read the RMS, or root-mean-square. We do this with a scope at our shop. Just hooking up a volt meter will not give you the correct reading. The resistor in the circuit varies depending on the temperature of the winding. As the voltage goes up, the temperature increases resistance. This keeps high system voltage as generator output goes up with engine speed from burning up the coil and points.