duraspark

IF you have installed duraspark on a 71 -351c please tell me where the white and red wires from the NPD harness hook up to . does the white wire go to the I or S terminal on the solenoid relay and do you disconnect the pink wire or not. the auto restomod diagram shows pink wire intact, white to I terminal and red wire connected to red/green stock wire going to + post of coil ????

There are several threads on installing Duraspark systems on the 351C engines.

I installed a Duraspark system onto mine using the NPD harness and a diagram from Mustang Steve (found in the threads), but wound up having to alter the installation slightly (moving the white wire from the 'S' to the 'I' terminal, or something like that - it's been awhile).

Another member (CZ-75) researched and discovered a different way to install the system, but it didn't work for me - I wound up smoking a couple of Duraspark boxes using his configuration, so I reverted back to my original set-up.

http://www.7173mustangs.com/thread-distributor-and-ignition-info-thread

Lots of good info in that thread... there are others as well.

Hope this helps.

I went out to my storage shed and dug out some old service manuals, including a 1978 Ford manual, to verify that the Duraspark II is directly connected to a 12 volt supply, and it is. The preponderance of the wiring diagrams I could come up with on the internet also show this, but I wanted to verify it myself.

I knew that the Duraspark module could not be connected in parallel with the coil, after running through the pink resistor wire. This would cause the Duraspark module to function from a constantly changing voltage source, and always less than 12 volts. Every time the coil windings charge up they place a load on the resistor wire and reduce the voltage to both the coil and, with this wiring diagram, to the Duraspark module. Additionally, the Duraspark module will add it's own load to the circuit, further reducing the voltage to both the coil and module.

As I suspected, the wiring diagram from NPD is not correct, nor is the statement that the module has to run through a 1.4 ohm ballast. The red wire that connects to the module must be connected directly to a 12 volt keyed source. The positive (+) wire that goes to a stock coil should be connected to the red/light green wire that connects to the pink resistor wire.

The white wire is connected to either the "I" or "S" terminal on the starter solenoid. The purpose of this connection is to retard the timing during cranking, with the blue grommet Duraspark II module. The brown or red/green wire that supplies 12 volts to the stock coil during cranking should remain connected, also.

EDIT: After thinking about it some, the brown or red/green wire that supplies 12 volts to the stock coil during cranking should NOT be connected to the same terminal as the white wire, or it will back feed into the white wire to the Duraspark module, potentially affecting timing. I believe it should only remain connected to the "I" terminal with the white wire connected to the "S" terminal. The "I" terminal provides 12 volts during cranking, only. When the brown or red/green wire remains connected it has the reduced voltage during run, when the coil is connected through the ballast resistor or pink resistor wire.

If you use an after market high performance coil or a Ford e-coil then bypass the resistor completely for both coil and Duraspark module.

White wire should only go to the S terminal, so it only retards timing while cranking.

Without dredging everything up from the thread I referenced above, there are a few different ways to wire it all up, depending on your car's factory wiring harness (and whether you have a factory tach or not, I would guess).

Mustang Steve has the retard function but no Tach signal provision.

John Ha's diagram shows that the tach will work but I question the white input being attached to the solenoid "I" terminal. From Mustang Steve's forum

Click to expand...

My car likes the second diagram better, since when I wired up according to the top diagram, it would only fire the engine while the starter was cranking.

CZ-75 and I both used the same NPD Duraspark wiring harness, but he did further research and discovered issues with their harnesses. He went further and found the issue, corrected it, and wired his car to function with the white wire on the 'S' terminal for ignition retard while starting capability. I attempted the same wiring configuration with good results initially, but then smoked 2 Duraspark modules shortly afterward. So I reverted back to my original running configuration (bottom diagram via the NPD harness) and it's been running great ever since without issues.