Resistor wire

Just dropped my new engine in and replaced the wiring with a new one from Z & M Jeeps. Really nice quality and US made. Everything plugged right in. But I do not have the required 6 volts to the coil in the run position, I have 12 all the time. I found the resistor wire in the harness and it does not appear to be a resistor wire. (no markings of any kind) So I unplugged both end of the harness and took a ohm reading and nothing, same as any regular wire, no resistance. I have a no starting condition after it is up to operating temp. and sometimes will shut off at low idle speeds. My question is this, what affects does constant 12 volts to the coil have on the ignition system? So far I have replaced ignition switch, coil, pick up coil in dist., starter solenoid and ignition control module on fender.

The stock coil will not handle full voltage, MC most likely not agree with doing the TFI conversion but the TFI coil will handle the voltage, for me it was cheaper than HEI as I had nearly all the parts, and there is some debate weather the stock module will handle full voltage, but when running the motorcraft box on these it's always wise to have a spare box along.

Just about any Auto Parts house should have a generic resistor that you can plug in-line if you want to run the stock ignition.

The OP did not specify if 6 cyl or V8.

In a V8 application, 12v has no effect on the Dura-Spark box. It is an issue with oil-bath canister type coils. These are designed for 6v (throwback to the old days...) Continuous 12v use can cause failure and even explode, hence the TFI upgrade.

When researching the TFI upgrade I read several accounts of cross-firing under the cap running @ 12vdc.

On the V8 cross-firing can be eliminated by running the Motorcraft dizzy and the 460 "big" cap and rotor. (MSD sells a kit) This also requires a new set of plug wires (Ford 460 set are about perfect). I ran a "cut to length" set. Kinda a PITA.

I'm not sure how to solve this on 4 & 6 cyl. Google "TFI Upgrade" and you should find a lot of information.

The best solution for my ignition was run the Motorcraft dizzy and MSD off-road CDI box (epoxy potted) Summit sells one for $150. I ran a MSD coil matched to the CDI box. This eliminated my reliability issues completely. I'm suprised how much water can pour on the cap and it runs perfect. Once I had the engine submerged to the valve covers!

Quite a bit of useful info Guys, appreciate it.

Received a call from Z & M Jeeps last night and here they discovered all the wiring harnesses made so far did not have the resistor wire put in them (they were not happy with the manufacturer) so today I spliced the resistor wire from my old harness getting my 6 volts to the coil on run and drove it all day without any problems. I'll put some more miles on this weekend just to make sure but don't expect any problems.