I will start off with the disclaimer that this 74 F250 has been pieced together like Frankenstein.

Facts:
1) Truck has wiring for elctronic ignition. Rewired for points ignition.
2) Came with points ignition and I had it running for a couple minutes. Now no spark at all.
3) When truck was running I needed to disconnect battery to get it to turn off, switch would not kill it.
4) Points, cap, condensor, wires and plugs were new purchased by PO
5) Coil does not have an internal resistor
6) Ran test light to tach side of coil and the light stays on when cranking.
7) Checked points gap with feeler gauge .017 and it seems to be ok.

Question:

I don't think the wire from the ignition switch is a resisitor wire. Would not having a resistor wire burn up the coil, points or both?

Eventually I will go to electronic ignition, in the meantime I just want to get the truck running so I can move it from the yard to the garage.

 

Without a resistor wire you're getting full battery votage (12-14v) which will burn up the points/coil in pretty short order.

The resistor wire reduces the voltage to 6-7v on a points setup IIRC.

 

He's right. The ign wire should be tan/brown in color and connected to the solenoid. Check it with a volt meter, believe mine read 7.2 volts. If its getting a full 12 volts it could fry the alternator quick too, it engages it.

 

This is incorrect; the two circuits are not related. Not sure what you mean by "engage" the alternator; if you mean "excite," then this is done in two different ways (depending on if the truck has an ammeter or an ALT light), but neither case is related to the hot-in-RUN circuit of the ignition coil. The only way to excite the alternator is to apply a signal to the FLD terminal while the alternator is turning.

The resistor is required on all points or Duraspark systems. It's also called a "ballast" and its job is to maintain roughly the same voltage at the coil regardless if the key is in START or RUN. In START, the coil is powered directly off 12 volts through the I terminal of the solenoid. But because the starter pulls the battery voltage down during cranking, the voltage at the coil falls below 12 in START. Without the ballast resistor in the RUN circuit, the voltage at the coil would jump to full voltage and be drastically different in RUN than in START.

The resistor wire drops the voltage at the coil to 6 to 7 volts in RUN and both the coil and ignition module (or points) are designed to operate with this reduced primary current. As MH said, eliminating the resistor limits the lifetime of the coil. In lieu of the factory-style resistor wire that would have been part of the original wiring harness, you can install a stand-alone power resistor (available from the parts store) under the hood. You want something close to 1.3 to 1.4 ohms.

 

Thanks for the info. I took a look at the wiring last night and the resistor wire has definitely been spliced under the dash. I am going to pick up a resistor from the parts store.

 

Heh Heh. I was wondering how long it would take for you to see this.

 

There are three possible resistor wires used in FoMoCo vehicles in the 1970's. None are color coded tan/brown.

COLF-12250-A .. Resistor Wire-Ignition Coil (Motorcraft DY-37).

61.49" long / Color coded PINK / 1.30-1.40 ohms resistance / #20 gauge wire.
---------------------------------------------------------------------------
D1AZ-12250-A .. Resistor Wire-Ignition Coil (Motorcraft DY-84-Y).

60" long / Color coded RED with GREEN stripes / 1.30-1.40 ohms resistance / #16 gauge wire.
------------------------------------------------------------------------------------------
D7AZ-12250-A .. Resistor Wire-Ignition Coil (Motorcraft DY-213).

49" long / Color coded RED / 1.30-1.40 ohms resistance / #16 gauge wire.
-----------------------------------------------------------------------
DuraSpark electronic ignition introduced in 1974, but not all vehicles came with it until 1976, as it depended on the applications.

1974/79 FoMoCo vehicles: The module used in 1974 is 1974 only / The module used in 1975 is 1975 only.

There are 3 possible modules used 1976/79. One was only installed in some specific sold new in CA vehicles.

Modules have ID engineering numbers marked on them and have a colored plastic square above where the wires feed out.

1976/79: The most common module has a blue plastic square. Specific CA vehicles have a red plastic square.

1979 LTD/Mercury Grand Marquis w/351W's & EEC. Its module has a brown plastic square.

 

I think Evans confusing the "I" term of starter relay with the resistor wire leaving ign switch.

 

I bought a 77 F250 4X4 with a 460 conversion. It had a "Frankenstein" element to it, too. The electronic ignition had been removed and most of the electrical connections had been replaced with junction blocks. The previous owner had installed a Mallory dual point distributor. I replaced it with a Pertronix Ignitor II module and coil. I eliminated the resistor and sent 12 volts directly to the distributor from the ignition switch as the installation instructions said. I put about 100 miles on the truck and it died. On a whim I replaced the coil with the one I had just taken off and it ran. Pertronix replaced the coil under warranty. I put the second one on and about 100 miles later it dies again. Put the old coil back on and it ran. Pertronix replaced the 2nd one under warranty. I called Pertronix and discussed my problem. The rep said it sounded like a grounding problem and told me to check all of the grounds-distributor, etc. The engine block was grounded to the firewall but, not to the frame so I added a ground directly from the block to the frame and replaced the coil, again. That was 2,000 miles ago.

 

I didn't want to be the one to bring it up, but "Frank" sounds like a perfect candidate for a pertronix 2 upgrade.

this will allow you to utilze the full 12v to the distributor, assuming you get it wired to the ignition switch correctly so you can shut it off.

for the $100 it would cost, this would be a very good fix to your problem. You could go back to DSII, but since it has been hacked, the Pertronix would be much simpler.

my 0.02 ...