These trucks did not come with what we know as a typical ballast-resistor (heavy coiled conductor mounted to a thick insulating ceramic base) but instead used a resistor-wire from the ignition switch to the firewall. From the firewall to the ignition coil it's just regular wire in most cases. I say most cases, because just recently someone was working on a truck (or maybe an old Bronco?) where the wire under the dash was normal and the section from the firewall connector to the coil was resistor wire. NEVER EVER have seen that on a Ford before, but like I always say, just 'cause I haven't seen it doesn't mean it doesn't exist.

But in any case, yours is a resistor wire and can be measured in ohm with a meter, or measured at the coil end in voltage. But for the voltage reading to reflect reality there has to be at least a few amps worth of load on it as well.

If you ordered a separate ballast resistor, do not add it to the circuit until you find out whether your resistor wire is still in place and functioning. Otherwise you could end up with even lower voltage than you'd want.

Paul

 

Post # 4, second sentence.....ballast resistor wire voltage test.

If you want to try a test for its resistance, we can do that, too.

 

For what its worth, back in college my '77 did the same thing to me. One of the wires in the distributor going to the magnetic pickup assembly had broken but had not shifted out of place - it was the bottom wire which is right under the top wire thus shielded from view. Took me forever to figure out what was going on but then I used a screwdriver to poke the wire and it moved out of place. Replaced the assembly and everything was fine.

 

Hi.....well here is what has transpired to get trucky to spark. Friend and I pulled dash and located the ballast resistor wire.....IT TESTED GOOD!! Since we had the dash off we cut out the original and replaced it with the new. All the wires in the loom looked like they were just installed, new. BUT, still no spark. 12 volts INTO coil. I am at a loss how this can happen after 40 years of faithful service. EVERY ignition part and module plugs have been replaced. I am at my breaking point. Friend suggested next visit we just try to install a ceramic ballast resistor on the fire wall and try that way to lower voltage. Any thoughts?
Thanks for all the tech advice!

Hunter

 

"Any thoughts?"

Yupp! Let's ferget about the ballast resistor wire for now and run the ever popular "blink test," OK?

Grab yer test light and hook one end to the TACH TEST (-) coil terminal, the other end to a good.. clean engine ground.

Have a helper crank over the engine whilst you observe the test light......you're looking for it to blink.

Whacha got?

 

To all who have been helping with no start.......... HELP! This is making me nuts. The NEW FORD ballast resistor wire reads 0 ZERO resistance, does that mean it is defective? My friend and I are at a stand still, EVERY ignition component has now been replaced 4 times REALLY! I am still getting 12.3 volts to coil. How do I get the required 6-8 volts into coil? Should we just put a 1.3-1.5 ohm ceramic on the firewall and see if that works? Local electrical specialist says a week to diagnose and $800 fee. ALL the parts I have installed was only $200. Trucky is supposed to 'retire' with me this year and she was ready to get all 'gussied' up.

Thanks everyone,

Hunter
Burbank, CA

 

NO BLINKY! PLEEZE don't say pickup module.......4 have been installed and 4 distributors.

 

No blinky means the coil isn't getting switched, isn't getting a trigger to be switched or it's plain old bad. You could Ohm it out to be sure...but......

....The stator (AKA pick up coil)is the next test....or we can test the ICM next...? Naw, let's test the stator, ok?

Pull the three wire male/female connector closest to the distributor and clean 'em up. The wires you'll be Ohming out have the male connections going into the distributor - make sure they're clean and the wires aren't messed up.

Ok, now the fun part - ohm out the ORANGE and PURPLE wires......the BLACK one is an ignition ground and should read infinity if you desire to ohm it out to one of the other wires.

Ohmage....you're looking for 400 Ohms - 700 Ohms between the ORANGE and PURPLE wires if the stator is good.

Whatcha got?

 

Just tested Orange to Purple and nice reading of 612 ohms. I am just worried about that 12.3 volts going into coil, the new ballast wire should have corrected that, but like I mentioned the new wire read 0 (ZERO) ohms. Ready for next test!

 

Ok....we know the stator is good.....next up is the ICM voltage test.

Disconnect the two wire (RED and WHITE) connection at the ICM. Make sure the wiring is good and the connections clean.

You should have 12 VDC with the key in RUN....at the RED wire from the ICM.

You should have 12 VDC at the WHITE wire from the ICM with the key in START.

Whatcha got?

IF you haven't done this already, ohm out the coil's primaries and secondaries, please.

We'll get to the ballast resistor wire soon enough....but you should have showed SOME resistance when you ohmed it out....like mebbe 1.3 Ohms.

 

electronics 101, if there is no current flowing there will not be a voltage drop across any resistance. that means you will read full voltage at both ends of a resistor or resistance wire, or ballast resistor if there is a break in the wire,,,past the point you are measuring.

sounds like you are getting power to the coil but not letting it get out and go to ground.

its been a long time since I messed with one of these systems, so I'll let the other guys call out the specific wires and tests.

if the coil is properly grounded you should be able to use an old style bulb test light and tap the + side of the coil and get spark out the top.

 

................Have you tested the ICM for voltage yet?

 

The testing sequence for your truck was posted. Did you follow it ? Also you may have a Dura Spark 1 system since you are in Cali. so then you are supposed to have 12V to the coil during run.
Do you still have the original igntion module that came off your truck ? What colour is the wire loom on the box ?

Go back to post 14 and follow the steps one by one. If you do that you will locate the issue.
These systems are extremely simple and it should be an easy diagnosis.

 

Hi....

Just tested ICM output..................ZERO, NADA, NOTHING. Both red and white. I don't know if I measured Ohms correctly from coil, both battery and tac from center distributor wire reads 7.85? If zero out of module, this is the 4th ICM as with all components.
Ready for next test!!

Hunter

 

I want to see how this turns out. Filthy Beast sounds like he knows what he's doing. Awesome troubleshooting!!