Installing a Motorcraft electronic distributor and TFI upgrade

This information applies to all engines that accept the Ford/Motorcraft Duraspark ignition, even though the example here is for an AMC passenger car. Thanks to all the people that have controbuted information, especially Paul Dornon who untangled for me the Ford solenoid stuff.

Pre 70-something AMC cars have mechanical points distributors, and later ones use the Presolite electronic distributor. By the later '70s, AMC switched to a Motorcraft Duraspark ignition that is much more reliable and easy to find.

Points are simply no good. They work OK at low RPMs, but are hard to maintain, and the condenser value is critical, and replacement condensers vary -- by design -- 20% or more, and need to be matched to the coil. It's a lost art, and a pointless one unless you need to run factory-original for some class/competition reason. In that case, go get a Pertronix or other invisible conversion. Points are nifty in a retro sort of way, I'm hardly in a position to criticize your choice of amusement.

The Prestolites are no good because they have a really crappy vacuum system, are unreliable, a poor electronic design (they don't tolerate long wires between the distrib and control box) and are hard to get. Plus there's no performance mods for them.

Caveat: the Duraspark is a huge improvement over the older systems, but the electronics box has been known to "mysteriously" drop dead. My first one lasted nearly 10 years, but died about a month after my alternator started acting up, overcharging the battery for about a week, before I detected it and changed it. Others have reported similar problems, at least one instance involving alternator problems. It may be peculiar to the cheap imported "clones" of the Motorcraft part. The GM HEI ignition (see below) doesn't have any of these problems (it may have it's own set :-) and is also available for AMC 6's and 8's. SAVE THAT OLD JUNK POINTS DISTRIBUTOR!! YOU'LL NEED THE GEAR OFF IT TO FIT ONTO AN HEI!!

Duraspark components

The Duraspark system consists of the electronic distributor and a control box. It works with the factory spark coil, distributor cap, rotors and wires. The TFI upgrade consists of a special spark coil, distributor cap, "HEI" style wires. You can add the TFI stuff later. The TFI stuff is described further down this page.

The Motorcraft has two round hard plastic connectors; the box is cast aluminum, with little fins; four wires go to the distributor.

If you're lucky enough to find late-model AMCs in a junkyard you can yank all the parts at once, but the good news is you can buy everything new for relatively cheap, except the funny connectors, whiuch you can get from a Ford car or truck.

AutoZone sells a cheap replacement box for $20 (Jan 2004) and this is usually what I do (I've converted four cars now).

The Motorcraft distributor is not much to look at. The one here is the dead stock factory job, see below for a simple upgrade. It's got a single-diaphragm advance unit. I use 1979 AMC 258 distribs in my sixes, they have a more-agressive advance curve than older ones, though I don't know which year would be best.

Rather than searching for a somewhat hard to find part that's 30 years old and likely worn out, I buy rebuilt distributors. Even with the crappy parts available today, they're at least a cleaned-up version of the best used. Before you put your old points distrib in the box as a core, pull the gear off! You or someone can use it for an HEI upgrade!

You can get the connectors from any Ford that has a Duraspark ignition. Unfortunately I don't know which donor cars; tell me and I'll list 'em here [1970's cars and trucks]. On my first conversion I cut the connectors off and used barrier strips, but that's less than satisfactory. I recently found an AMC Concord donor in a 'yard and swiped everything from that.

Physical installation

Installation is nothing special: the distrib installs normally, bolt the electronics box to the fender, away from headers and exhaust manifolds, heat will kill it. I had no problems with the AMC 304 V8 or 232 six.


This will be where your effort goes, though it's not very hard. You can either wire it directly with standard wiring parts (I did this on my 1963 Rambler) or you can go to a 'yard and strip out the connectors from a late 1970's/early 1980's Ford car or truck. If you're lucky you'll get the control box too. You want the two connectors for the control box and the one for the distributor.

The black wire is ground. A solid, perfect ground connection is absolutely required. Crimp (and solder, if you can) a ring terminal to the wire, find or drill a hole on the fender, sand to bare metal around the hole, and tightly bolt the ground wire to the fender. I paint the ground connection afterwards to keep out moisture. All coil current and the returns from various signals goes through this connection, it must be good.

Orange, violet and black wires go to the distributor: match up the colors. (Orange and violet are the reluctor coils, black is distributor ground).

The green wire goes to COIL (-), where the points went if you had those.

The red wire goes to IGNITION, switched battery voltage that goes OFF when the ignition switch is off. This is power to run the Duraspark module. Please note that in a lot of points-ignition cars, what looks like a simple switched ignition hotwire is in fact special resistor wire buried in the harness!!! DO NOT USE THAT WIRE. Red must get full battery voltage. How to tell? Get a factory Technical Service Manual... or with the car ON but not running, ground coil "-", and measure the voltage on coil "+". If there is a ballast wire or resistor the voltage on coil "+" will be less than 10 volts.

The white wire is "spark retard". This wire goes to the post marked "I" on a Ford-type starter solenoid (as used in AMCs). Battery voltage appears on that post only while the starter is cranking. This crudely retards the spark for easier starting. On my '63 Classic I left this wire off, it's been fine for 10 years. It definitely won't hurt to add it.

The starter solenoid (Ford type) is involved in the ignition system, besides the obvious purpose of operating the starter motor. There are three connection posts to the solenoid, besides the big cable studs. One post goes to the START position on the ignition switch, and operates the solenoid. The remaining two involve the ignition system.

Solenoid post "S" is similar, it outputs battery voltage directly to COIL "+", temporarily bypassing the ballast resistor to provide a hotter spark during cranking. You car will run without these connections, but they improve performance overall, and you should make the effort to use them.

COIL "+" goes to the ballast resistor or resistor-wire, which in turn goes to the ignition switch. The Duraspark module must be used with a ballast resistor to limit coil current or you'll stress it and make it fail. Ballast resistors match the coil.

When splicing wires, such as splicing in the Ford harness, I STRONGLY recommend stripping each wire about 3/4", twisting in-line and soldering, first slipping a piece of heatshrink tubing over a wire first, and shrinking it down after soldering. This is electrically and mechanically superior when a splice is to be embedded in a harness. Crimps (butt splices) work OK, but are prone to long-term failure, as atmospheric moisture will cause electrochemical corrosion over time. NEVER! use electrical tape to insulate splices (adhesive dissolves, tape creeps, cold-flow may cause pierced insulation months/years later!). NEVER! twist wires together without soldering them!

Here's the schematic if you're wiring it yourself.

GROUND:                 metal box       screw to fender for ground 
SWITCHED BATTERY:       red             to ignition switch
COIL (-):               green           where points went
CRANKING +12V:          white           see text

DISTRIBUTOR:            violet, orange, 
                        black           match up colors to distributor

                to solenoid "S" post
                |    to switched IGNITION power
                |    ^ 
                |    |    to solenoid "I" post
                |    |    ^ 
                |    |    |
                |    |    |
                |    |    |          +-----------------+
                |    |    +--- wt ---|                 |
                |    |               |    DURASPARK    |--- or ---> to 
                |    +-------- rd ---|     CONTROL     |--- vi ---> distrib.
                |    |               |       BOX       |--- bk --->
                |    |    +--- gn ---|                 |
                |    |    |          +-----------------+
                |    R    |
                |    R    |   <--- RRR is ballast resistor
                |    R    |
                |    |    | 
                +----+    |
                     |    |
                     |    |
            coil "+" |    | "-" coil
                   |        |
                   |        |
                   |        |
                   |        | spark coil
                   |        |

bk      black
bn      brown
rd      red
or      orange
yw      yellow
gn      green
bl      blue
vi      violet
gy      gray
wt      white

(It's not of general use, but some kind person derived a schematic of the innards of the Duraspark control box.)

TFI Upgrade

I don't know why it's called that; TFI stands for "Thick-Film Integrated", a type of integrated circuit, probably used in some later-model ford ignition. All we want is the fancy coil, cap, rotor, adapter and wires.

The TFI upgrade is unbelievably easy. The "hard" part is bolting the coil to the fender somewhere. I suggest getting a used coil from a Ford truck or car. They don't wear out (though the plastic around the connector is easily broken; they will still work fine though) and new coils are $60 (in 2004). The other parts are best bought new and are not expensive.

The part numbers for the AMC six (199, 232 or 258) are below, or you can ask for the parts for a Ford 300 ci 6cyl, aka 3.8l, 1977-1982 (plus others), and light truck 1977-1986.


brand part number


Standard FD151X


Standard FD155


Standard FD118


Standard 6643

TFI coil plug

NAPA/Echlin ICC1

TFI coil

Standard FD478

The plug wires listed above are 8mm, "HEI style" connectors, and comes with both flavors of spark coil wire (old style and TFI both) and even comes with #1 plug boot angled to clear A/C compressors. How cool is that?

NAPA sells the plug that fits onto the TFI coil (see above); it's cheap, and you want one. All the used ones I saw looked like crap.

The adapter screws onto the distributor where the old cap did; the new cap clips onto the adapter. The rotor goes where rotors always go. Here's some pictures for the terminally lazy:

Other notes

Here's the story with ignitions: the coil converts low voltage to high (spark) voltage by building up a strong magnetic field inside the windings of the coil with battery voltage, and then turning it off. The spark happens when the "field collapses", eg. when the current goes OFF. When the battery power is applied to the coil, via points, for instance, the coil essentially "charges up".

Here's the problem: charging up the coil takes time, a small fraction of a second, but at 5000 rpm there's not really enough time to charge the coil, that's why the spark output drops. This is plain old physics.

Points are mechanical, and so when the open/close quickly, they bounce. Plus, the arcing that occurs corrodes them, so their resistance goes up, and the coil doesn't charge up right. Points "fans" know all the tricks; strong springs, dual points (remember those!), favorite condensers. Ugh.

Electronic ignitions come in two types. The Duraspark is basically a "points replacement". Where points would ground the (-) side of the coil to charge it, so does the Duraspark (green wire). Spark timing is determined by the magnet and coils in the distributor. No arcing, no wear, no dwell, etc. Spark energy does drop off at high speeds, due to not enough charging time, but no longer from points crapping out. A huge improvement!

The third type of ignition gets around the coil-charging problem through other means. For a given coil, even if you allow enough time, the amount of energy stored in the coil is limited by battery voltage, 12 to 14 volts. "Capacitive Discharge" and other schemes internally produce 100 volts or more, and dump that into the coil come spark time. There are other subtleties involved, but that's the essence.

There is also the HEI ignition, swappable into AMC sixes and eights. Apparently it's a drop-in EXCEPT! the gear on the end of the shaft must be removed and replaced with one from a points ignition. Don't throw them away!

The Duraspark allegedly provides 50% more ignition power, using the TFI coil, than HEI does, so why bother?