All of the old wiring has been taken out so we’re looking at a blank slate. I don’t plan to start installing the Ron Francis wiring kit until after the cab paint and body work is done but I do want to run and break-in the engine and power train. Thus, what I am looking to do is come up with a minimal wiring system that accomplishes little more than that basic task.

Here is what I have to work with: an MSD Digital 6AL ignition control system, an MSD Blaster coil and an MSD Pro-Billet Ford FE Distributor and the stock ignition switch.

Also in the mix is a one wire alternator, a PowerMaster 9506M starter and an AutoMeter tachometer.



Here are the wires that plug into the back of the ignition switch. I have looked at dozens of images and diagrams of ignition switches that are supposed to be from a 1976 F-150 but none look exactly like this. I’d like to discard this part and simply use bayonet connectors on the base switch to simplify things.



So what is the minimum that needs to be done so that this switch will support only starting and running the engine?




The switch will be grounded to the dash so 12V+ will have to be brought to the switch. What gauge wire and which blade should that be connected to? A wire will have to go from the switch to the S post on the Ford Solenoid for start/prove out - same two questions. No accessories so we can skip that, right?

So what happens when the switch goes from Start to On? Does the Ford Solenoid continue to provide 12V via the I post? Will this all work with just two wires?

 

The I terminal only has power during cranking.

 

Thanks for the swift response. So what connection keeps the engine running?

 

 

Is the blank slate state of wiring purely the ignition system, or is it the entire truck system ?

Will you be driving the truck in order to break in the power train ?

If yes, are you happy with the wiring for brake lights etc, etc ? (These will be accessories.)

The Blaster coil has 1.5 ohms resistance. Does the dizzy ohms match this ? (It should.)

Does the alternator have a blade fitting on the casing in order to attach a ground wire to an alternator warning light ?

If no, and you want a warning light, it can be done.

Will you be temporarily wiring the tach ? (This would be an accessory.)

The ‘I’ terminal on the starter relay is redundant. Ignore it permanently.

The ‘S’ wire will be the same gauge as the red/blue trace one. (14 or 16 or 18 gauge ?)

(It carries basically no load, hence it is way thinner than the black/yellow trace wire.)

The ignition power wire will also be a thin gauge.

The thicker 12v+ and 12v- wires feeding the 6AL can be the same gauge as the ‘heavy red’ and ‘heavy black’ wires exiting the 6AL in the drawing. (I see no mention of a fuse in that circuit in the diagram.)

Do you own a test light ?

Will you be using the ignition switch with the new wiring kit ?

Do you happen to have a starter switch (push in) and/or an on/off switch lying around ? (It’s an alternative option if needed.)

Is the switch an off/on/start setup, and once started, the key would return to 'on' ?

Some of the questions appear dumb, but I make no assumptions when working with electrics, hence the questions.

 

Every wire from headlights to taillights was removed. The following items have been replaced: battery negative (AWG 4 grounded to engine block and, from there AWG 4 to frame, battery positive: AWG 4 to Ford solenoid. Alternator (AWG 10 to ground, AWG 10 to A side of Ford solenoid, AWG 4 from B side of Ford solenoid to starter solenoid (AWG 10 jumper). In other words the starter circuit has been reestablished and tested with sparkplugs out using a triggered starter switch. The starter circuit works.

No, the plan is to first break in the engine w/ temp mufflers and front/rear wheels off the ground (2K RPM avg for 30 min) followed by TCI recommended transmission test and fluid level verification (2 gallons in now w/ 1 gallon to go), followed by observing rear axle movement at low RPM. Finally, Saginaw pump will be connected to test Power Steering and Hydroboost.

N/A

MSD states that all three MSD components that will be used here are compatible with one another.

No it does not. There will be a volt meter in the full re-wire project that is reported on the face of the Dakota Digital dash. This is a "one wire" alternator that has an AWG 10 ground wire and an AWG 10 wire to the positive side of the battery.

That can wait. The primary goal is to break in the engine and identify any serious issues that need to be addressed before further work is attempted.

Yes, I will probably use an aligator clip to the + battery terminal for this. Long term the tach output will be reported via Dakota Digital dash.

MSD shows the 'I' terminal wire (that formerly went to the original + coil wire) is shown by MSD to be connected to the lighter weight red wire on the 6AL box.

Yes but I need to figure out which blade on the stock Ford ignition switch to connect it to.

​​​​​​​According to MSD, that connects to the thin red wire on the 6AL box.

MSD shows these two heavy wires being connected directly to the battery. I plan to follow that.

Yes and a multimeter as well. Continuity testing might identify the blades in the switch housing for me as follows:




Not sure yet. The key also fits the door lock but that doesn't necessarily cinch the decision that will be made at a later time.

Yes I do have a "Racing Only" switch on the shelf. It could be a fallback option I suppose.

Yes, moving the switch to start/prove out will spring back to the ON position upon release. This, I believe, is stock behavior.

As they say, "There are no dumb questions."


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You can't get more detailed than that !

I think it best to play it safe and simply determine which blade is live at the off/on/start positions.

The 'live' circuitry is within the switch, so there should be no problem fitting the switch into a vice, and thus leaving both hands free.

Here's my suggestion :

Connect a wire from the battery + terminal, 18,16,or 14 gauge is fine, to the black/yellow trace blade.

Connect one side of the test light to the battery ''-'' terminal, and the other side (clip?) to each blade, in the off position.

Then do the same in the on and start positions.

I expect the red/blue trace blade to light up in the start position, so that blade would connect to the 'S' on the starter relay.

The thin red wire ''from the ignition key'' in the diagram will connect to a blade that lights up during ''on'.

Post up which blades light up when, and then we can determine how to connect the ignition wire to the start section.

Once you have ascertained which blades do what, you can use the switch permanently with your new wiring.

Depending on the new wiring, the switch may no longer carry heavy loads.

 

Although you only need temporary ignition wiring at present, you will need a fuse in the above circuit at some point.

Now is a good time to fit one.

AWS 10 has a rating of circa 50 amps, I think ( ), so a fuse rating LOWER than that would be required. (Say 40 amps)

What is the rating of your alternator, as I suspect it would be higher than 50 amps ?

I like the AWS 4 to grounds, but no mention of cab and bed grounds. Please check that.

I have a one wire alternator and a volt meter, but I liked the idea of the warning light at start up, and connected one.

Yes it's optional for sure, and you don't need one now, but now is the time to consider the cosmetic stuff that might be desired later.

Once the 'on' terminals have been ascertained, the tach can be connected along with the ignition wire to the chosen terminal, thus avoiding the need for an additional wire to the battery.
(The tach ground can simply go to a bolt on the cab near the dash area.)

I'd use a 3 or 5 amp fuse on the tach and ignition circuits, now temporarily, and permanently in the final circuits.

 

6X8: Agreed that fuses are needed. One each at the tach and alt (100 amp) for sure. I will need to check the MSD docs re the hot wire to the 6AL box to see if that's not handled internally.
Re grounds, the cab is explicitly grounded to the frame with a braided strap. Hood also using the stock strap.
Good idea to test and map the switch. The continuity testing will tell if the internals of the switch are OK (the switch worked before despite POs butchering) but the I/O testing you suggest will confirm actual performance.

ALL: I have done some additional sleuthing and come up with a more informative picture of the blades in the switch and the function/size of the wires I plan to attach bayonet connectors to and then route as appropriate. Here is the updated picture:


Clearly the heavy yellow wire brings 12V from the battery, the heavy black wire with yellow trace is for accessories so can be ignored/skipped and the S wire goes to the S post on the Ford solenoid.
Note that there are TWO wires associated with the I blade (ignition) and that they are of different thicknesses (AWG 12 & AWG 10). My MSD diagram really doesn't tell where those two 'I' wires might go. Also, where does the P wire go?
We are closer to a solution but not quite there yet.

 

Please make a note to review the wire from the starter relay to alternator amp rating.

50 amp wire will work now no problem.

I tried looking at my wiring diagrams earlier, but alas, I need a magnifying glass.

Good, the switch source and start wiring is sorted.

The 10 + 12 gauge ignition wires were for the OE setup, and you can definitely go thinner.

I wouldn't worry about the P wire at this stage, but it would be useful to know when it is activated (on or start?).

What is the MSD 6AL part number ?

Something caught my eye and I forgot to question it.

 

I might not need it if this diagram is correct :

 

The above MSD diagram looks to be correct.

The OE coil '+' wire would have power 100% of the time when the key is 'on'.

The diagram below is what caught my eye.

Do you understand why the 'I' connection cannot be used ?

 

Do you mean the two in the switch ?

If yes, don't worry about it as they are for an OE system.

The MSD diagram only shows one wire, the small red one.

We still need a wire that feeds the ignition from the start position, but that will become obvious once you've ascertained what terminal gets power and when.

 

This discussion has been very helpful to me and I hope that it is useful to others in the future as well. I think that I have a decent grasp of a solution that may well test out positively. I will revise my diagram and publish it here. I have some traveling to do so will be off line for a week or so. Nailing this down will be my top priority when I return.

 

Here is my revised minimal ignition system diagram: