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8n ballast resistor appears to not be working

H

Hatchetman1984

New User
Hey guys, i went out and purchased the OEM
Ballast Resistor, and not the generic "ceramic"
kind. My ballast resistor is what Dell(WA)
calls the "infamous ballast resistor".

My problem is it doesn't appear to work - at
all. It measures 12 volts on each of the posts
when hooked up to a 12 volt charger. Shouldn't
one of the top posts cut the voltage down to
protect the points?

I am running a 12 volt coil on a 1948 Ford 8N.
I know the coil is 12 volts because i ordered
it from here. Alternator and everything else
works fine. tractor runs fine. I am battling an
issue with starting. My other post mentioned
that with the resistor hooked up, the tractor
would only start once you let off the starter
button. With resistor unhooked, it fires up at
like the 1st or second crank - almost
instantly.

Can someone show me a diagram of how the
Ballast Resistor is to be hooked up and explain
it in layman's terms? I'm not very good with
electronics but at least on the ceramic
resistor i had before, i had 12 volts on 1
side, and 8 volts on the other when it was
installed...
 
here's where understanding ohms law would help.

When no current is flowing.. no voltage drops.

if you have a 12v battery, and wire one post to 10 different resistrors all end to end.. then take a volt meter and measure the end of that resistor chain referenced to the other battery post.. you will read full battery voltage.

now, instead.. hook that ressitor chain to the other battery post so it makes a loop.

then each resistor will have a voltage drop.

the fact you measured bat voltage on both sides at least tells you that it has continuity.. ansd as soon as you install it and test it correctly.. it will likely be ok.
 
I sort of get what you are saying. I am not sure what wire is supposed to go to the bottom post. Is that a ground? There are two posts on top that i just assumed one side had the 12 volts going into it, and then the other side cut the fire back going to the coil...

POST----------------- POST


BOTTOM POST

?
 
wire from power hits lower post. key has 2 wires. one wire to lower post one wire to one upper post. other upper post to coil.

voltage ONLY drops when points are closed and current is flowing. when it is an open circuit. no voltage drop
 
just like Soundguy described..blacks to key sw & upper right out to coil, always hot power to lower
 
Well it is hooked up EXACTLY like the picture
above, and i've noticed no change. The
resistor is warm to the touch. It's been
running for about 5 minutes now and as best I
can tell, this just must be a bad oem resistor.

After 5 minutes it's got 12 volts going to the
bottom post, 12 to the upper right hand post,
and the post that sends the wire to the coil is
at 12 volts. So i'm going to order another one
and go from there.

At least with the ceramic resistor, it was
working. It was hard to start because of having
to time the release of the starter button, but
at least the resistor worked. I've ordered bad
parts before at auto parts stores, so maybe
this is just a bad oem resistor....
 
" I've ordered bad parts before at auto parts stores, so maybe this is just a bad oem resistor...."

Yep.

And likewise, many of us have ordered parts we didn't need because we failed to properly troubleshoot the problem.

I doubt the problem is your resistor.

Go back & re-read soundguy's reply.

You need a LOAD on the circuit.

It appears from what info you are providing that you aren't measuring it correctly.

Measure voltage with the points OPEN (no load) then measure it again with the points CLOSED. (with load)

Post back & tell us what you find.
75 Tips
 
just because you don't know how to measure it doesn't mean it is bad.

points MUST be closed to measure the voltage at the coilAND see the v-drop from the resistor.

the fact she runs means the resistor has continuity... the fact she is warm means she is disipating power ( watts) heat energy.. that energy is coming from the current flowing thru it... that means the resistor is not a dead short.

we can thus determine the resistor is neither shorted nor open, and it radiates waste heat, so is flowing current and is thus 'working;.

go ahead and keep buying parts if you like.. but it would be better to actually correctly test and uderstand the parts you have and how they work.

keep us posted!
 
thanks Bruce; i live in a round coil world. reason i was asking is beacuse of an imminent 12v conversion (not beacuse of starting or charging problems though) and i thought when doing that if i went to a 12v coil i wouldn't need to add a resistor.

guess i should spend more time browsing your 75 tips instead of asking silly questions.

i jsut have to ask though; do you have all of them memorized or just real close to it? all the work you put into the compilation wouldn't surprise me at all if they were memorized.
 
" i thought when doing that if i went to a 12v coil i wouldn't need to add a resistor. "

Will your conversion be w/ a round coil or square coil? A true 12v round coil (as in a NAPA IC14SB) needs no resistors.

If your conversion is w/ a 12v square coil, it does need the OEM ballast resistor.

" do you have all of them memorized or just real close to it?"

HA! At my age, I'm doing good to remember what I had for breakfast! :)
75 Tips
 
round coil; 1954 naa.

doing the research recently. see our sponser has a seemingly reasonable priced kit. would go with the 12v coil just to simplify things. don't want to get to deep into it now and hijack this threrad.

your 75 tips - the frequent refrance to them - reminds me of something i've heard time and agin. don't need to have all the info memorized but you DO need to know where to go to find it. thats why i'm here. thanks to all the folks that pass on their knowledge.
 
Excellent advice here, do what they say. To me a "non-working" resistor, like I had on my 9N, is one where there was no continuity, measured with an ohm meter, through the resistor, meaning it won't start or run at all.
 

Most of the time they do fail open, not shorted.

But if you have an ohmmeter, you can check the resistance to see if it is in spec or not.
 
(quoted from post at 20:37:17 09/09/14)
Most of the time they do fail open, not shorted.

But if you have an ohmmeter, you can check the resistance to see if it is in spec or not.
Click to expand...

Actually an ohm meter can check for all three scenerios.

[list:d6993f51b7]Open
Short
And if within Tolerance[/list:u:d6993f51b7]

If you grab a handful of those ceramic resistors, I bet you they all measure different but within tolerance.
 
(quoted from post at 17:11:49 09/05/14) just like Soundguy described..blacks to key sw & upper right out to coil, always hot power to lower
Click to expand...

Once again my dislexia gives me problems when there is an elimination of something that is "obvious and common knowledge" The bottom post is just a junction?
 
(quoted from post at 08:38:43 09/26/14)
(quoted from post at 17:11:49 09/05/14) just like Soundguy described..blacks to key sw & upper right out to coil, always hot power to lower
Click to expand...

Once again my dislexia gives me problems when there is an elimination of something that is "obvious and common knowledge" The bottom post is just a junction?
Click to expand...

Yes. It is the same as connecting all the wires togather using a wire connector.
 
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