1974 F100; does it have one? Anybody know where this little gem might be so I can apply closer scrutiny upon it? Unilite says I just "HAVE" to have one....so I need to check, as I am not getting any sparkum to the plugs. Thanks...


The LaptopGeek -----
1974 White F100 Custom Fleetside
460 bored .040 over & C-6 automatic 2WD
Lunati cam, L&L Headers / mounts
Holley Avenger 770CFM & Edlebrock RPM
Plush black leather 40-20-40 bench seat
38 gallon JC Whitney fuel tank

 

Not sure exactily where the resistance takes place in the wire, but you can check to see if it is still working by using a volt meter. Switch the ingition to "ON" and check the voltage at the coil's "BAT" or "+" post. You should get a reading of about 6-7 volts assuming your battery is fully charged to about 12 volts.

 

The power wire to your coil has a resistance built into it-I'm not really sure it is anything visable.Using a voltmeter,check voltage at coil "batt" or + terminal with key on-should be between 4.9 and 7.9 volts.Your resistance wire is OK if your within that range.Did your truck originally have points or did it have that early pre-Dura Spark 11 breakerless ignition?

 

Whether the truck came with points or the Duraspark, the resistance wire is pink coming off the ignition switch. It is usually covered in the black braided material, with the wire being marked. They can and will go bad, especially noticeable with Mallory Unilite distributors. New resistance wires are available from the parts stores, if they know how to look them up. Usually listed in ignition resistors.

 

The wire is pink or red with black stripe, I actually think it was a green stripe from the factory but heat changes colors The wire is usually a burnt looking black in most of the old trucks I have worked on It says "resistor wire" every 6 inches or so, unless that is burnt off too
It runs from the ignition switch to a splice just before the firewall on the inside of the truck, right above your left foot. On this splice is red/green striped wire that runs direct to the coil and a brown wire that comes from the "I" of the start relay providing 12 volts direct to coil for starting only.
So with the key to start you get 12 volts direct to the coil, and with the key to run you should get, correct me if I am wrong, 6-9 volts at the coil.
I replaced the resistor wire in my 73 with a 1.40 Ohm ballast resistor, from a Do*ge, mounted under the hood where it is easy to get at and less prone to burning up and taking other alot of wires with it. Been there done that.
Have fun. And hope this helps.

Sparky

 

Sparky, LikemFords, Kenmt & 460V10.....

Thank you so much for your posts. You have been a great help - now if I can only do so well for somebody else....I'll go home tonight and pull out the volt-meter. Wish me luck - there might be a lot of SAD S10 owners come this week-end.....(all frowning in my tire smoke...). Color me Gone.....

The LaptopGeek -----
1974 White F100 Custom Fleetside
460 bored .040 over & C-6 automatic 2WD
Lunati cam, L&L Headers / mounts
Holley Avenger 770CFM & Edlebrock RPM
Plush black leather 40-20-40 bench seat
38 gallon JC Whitney fuel tank

 

Sparky - I love your posts - you are always right on the money when it comes to electrical stuff...


The LaptopGeek -----
1974 White F100 Custom Fleetside
460 bored .040 over & C-6 automatic 2WD
Lunati cam, L&L Headers / mounts
Holley Avenger 770CFM & Edlebrock RPM
Plush black leather 40-20-40 bench seat
38 gallon JC Whitney fuel tank

 

Sparky's right (as usual). Finally found the '74 wiring diagrams. Resistor wire is red w/ green stripe, spec. is 1.30 to 1.40 ohms for the Duraspark which was the same for the earlier point systems. The later Duraspark II systems still use a resistance wire but at a lower 1.05 to 1.15 ohms for more current. The coil changed too with lower resistance windings to match.

Barry

 

BBB - thanks for the confirmation with the schematics. I wish I had me a set of them things. I can tell you how to fix your computer, but I can't read car schematics.....

The LaptopGeek -----
1974 White F100 Custom Fleetside
460 bored .040 over & C-6 automatic 2WD
Lunati cam, L&L Headers / mounts
Holley Avenger 770CFM & Edlebrock RPM
Plush black leather 40-20-40 bench seat
38 gallon JC Whitney fuel tank