[AT] Ford 8n Under Dash Resistor?

Ronald L. Cook rlcook at longlines.com
Wed Jan 7 11:02:33 PST 2009


Some how or other, that Ford resistor puts battery voltage, or as near 
as possible to the coil when cold.  As the resistor heats up, the 
voltage is cut back.  I think they are called variable voltage resistors 
or something.  They get darned hot and have a heat shield around them 
for a good reason.  Chinese replacements won't work very long.  Also the 
lead to the coil needs to be in excellent condition and sized properly. 
  It is an interesting and cheap system that really has to be maintained 
properly so the Ford will start quickly under all conditions.  Any place 
that can lower the voltage such as the switch, wire, connectors, etc. 
can really put an adverse effect to starting.  Set up properly, those 
Fords will practically start before you can think about it.  Most just 
crank the battery dead and make the operator cuss.

Ron Cook
Salix, Ia

Dudley Rupert wrote:
> The wire is a good idea, Steve.  If the coil resistance were measured then a
> piece of wire with a resistance roughly 150% of that of the coil would be a
> good starting point.  The objective here is to get a voltage drop across the
> wire of 5 volts.  If the drop is greater than 5 volts then shorten the wire
> and if it is less than 5 then lengthen it.  If a guy had a low ohm wire
> wound potentiometer (variable resister) that might be fun to try too -
> 
> Dudley
> Snohomish, Washington
> 
> -----Original Message-----
> From: at-bounces at lists.antique-tractor.com
> [mailto:at-bounces at lists.antique-tractor.com]On Behalf Of Stephen Offiler
> Sent: Wednesday, January 07, 2009 5:14 AM
> To: Antique tractor email discussion group
> Subject: Re: [AT] Ford 8n Under Dash Resistor?
> 
> 3 volt coil... that's news to me, too.  Thanks Mike.
> 
> If originality is not a goal, but reliability is, you can sometimes
> replicate the function of a wirewound resistor with a coil of regular
> wire.  Depending on the resistance value needed, it might or might not
> be practical.  Of course, the gage and length of the wire are two
> critical variables and some math needs to be done to get it right.
> 
> Steve O.
> 
> On Tue, Jan 6, 2009 at 4:46 PM, Mike Sloane <mikesloane at verizon.net> wrote:
>> Ron Cook is correct - the original resistor that sits behind and below
>> the instrument cluster is to reduce the voltage to the coil - the old
>> front mounted coil/distributor (found on very early 8Ns) is a 3 volt
>> coil and it will overheat and burn out if subjected to the full 8 volts
>> for very long.
>>
>> I have not had good luck with the replacement resistors that I have
>> purchased from places like Valu-Bilt - they fail "open" after a short
>> time in operation or even when the tractor is stored.
>>
>> Mike
>>
>> william.neff.powell at comcast.net wrote:
>>> Hello,
>>>
>>> My brother-in-law let his 8n sit for about two years. Before he let
>>> it sit I had given it a tune up, carb rebuild, points, condenser, oil
>>> changes, plugs, coil, and I had it set up for 8 volt, it was
>>> previously 6 volts. Took generator to local auto-electric shop and he
>>> set the regulator for 8 volts.
>>>
>>> So, it had been sitting un-tarped for a while. I kept bugging him to
>>> get it going. Last Sunday I helped him start it. Bought a new 8 volt
>>> battery, opened the petcock and fuel started dripping out of the
>>> carb. Took the carb apart, lots of oxidation, was starting to
>>> varnish. Cleaned that out.
>>>
>>> It would not start after cleaning the carb. Checked the spark, there
>>> was none. Before bothering with take the distributor off (which is a
>>> pain as most 8n owners know) I checked the coil line for voltage
>>> using his headlight wire because he had no voltmeter. No light.
>>> Started tracing the wire back from the switch, I had light at the
>>> switch. Then I noticed a small block under the dash that had a
>>> wrapped wire resistor. The ignition toggle switch (no key on tractor)
>>> sent a wire to the resistor and after the current went through the
>>> resistor it was on to the coil.
>>>
>>> So, that little resistor was rusted out and useless... I bypassed the
>>> resistor and the tractor started right up.
>>>
>>> Is the resistor necessary? I'm guessing it's there to stop the points
>>> from frying up? Or it is in there to compensate for an 8 volt system,
>>> although I put in the 8 volt system  I did not add the resistor. (Who
>>> knows if it was 8 volt in the past?)  If the resistor is necessary
>>> where can I find one?
>>>
>>> Regards,
>>>
>>> Will Powell Pottstown, PA
>>> _______________________________________________ AT mailing list
>>> http://www.antique-tractor.com/mailman/listinfo/at
>>>
>>>
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