Alternatively, you might be able to simply use a 1N5408 on wire 32 Red-Blue (Starter Solenoid) and wire 732 White direct to the MSD box.

If current is more than 3amp (1N5408 according to the wikipedia page), another diode can be used... this would simplify this circuit to a single diode.

I picked the 1000v diode because of transient voltage conditions that exist in these old truck that might blow a lesser rating diode.

Oh, and the Flyback diode is optional but does cut down on those transient voltage spikes. They can be heard on the radio as clicks and pops when you turn stuff on and off. I installed them on all my own relays cos I'm weird.

Edit: Oh, whatever you do... These wires have no fuse protection, except the fusible links! Something else to think about...

Last edit, ah swear! : Ok, read up on another forum about current usage on the MSD boxes, and I went back to check the wiring schematic on that box. I think you can get away with just a couple Diodes to tell the MSD box to turn on and draw current from the Battery Feeds. No relay needed! If your paranoid, use a couple 3 amp weather proof inline fuses and a couple 1n5408 diodes wrapped in heat shrink, and I think your golden!

 

Ok, I'll try to,piece this together with the last one. I can do simple wiring stuff: I used to pull telephone wire and i build cables for my ham radio, but once I passed the general exam i pretty much forgot it all.

 

To make sure I understand:
I need to put a three amp fuse on the heavy red wire from the MSD to the + battery. I need to put a diode on the red wire and connect it to one or both of the wires coming out of the switch. Wouldn't that be the same wire that sends juice to the coil? I looked up these diodes and I'm not sure how to do this. They look VERY thin. If I cut the wire, do I splice in a diode and heat shrink it over in a loop tied off or what? I can't imagine that even soldering a diode into the wire is going to give it enough strength if it gets tugged very hard at all under the hood.

The more I look at all this the more lost I get. Why doesn't this ignition module just work when you plug it into the right wires? I have never heard of anyone splicing in diodes. I'm not saying it's wrong, but no one has ever told me it was necessary, which is pretty frustrating since it seems to be a plug and play type thing.

 

Oh no! that Heavy Red goes to the battery, in my searching I think that can draw around 30 AMPs of POWAH! holy 1.21 jiggawatts!

The diodes should go onto the "Red to swtiched 12 volts" Like in the schematic I posted before, except those diodes feeding a relay, it's feeding the MSD box.

That "Red to switched 12 volts" wire tells the MSD to turn on and do it's thing.

And, I would use a couple 3 amp fuse holders to feed the diodes...

so:

Ford Connector wires 32 and 732 --> 3 amp fuse holder --> 1N5408 Diodes ==> diode ends twisted together and then soldered to MSD's "Red to switched 12 Volts"

The Diode Bands are towards the MSD box.

Here's a picture of a not assembled wire and connector and wrong connector, but to show how it's setup:



edit: The reason I had to use diodes with my efi computer was that there was no wire I could use that had power in run and start. Doing it this way with diodes prevents any power backfeeding other circuits causing weird problems.
Maybe the MSD box is built to stay powered while it's being started, I donno... maybe try connecting just wire 732 (White) and see if it starts?

 

You have gone way out of your way to help me and I really appreciate it! I hope i can return the favor sometime.

 

Hey, No Problem!

If one person keeps their truck awesome because of my help, is enough reward for me!

 

Edit: Double post!

 

After looking through the diagram, is 32 Red/Blue a ground wire? Look where it connects on the coil and the starter relay.
And I think 16 Red/Green is the constant Run wire.

Im trying to find out the difference in 734 Orange/Yellow and 735 Purple/Blue. I understand 733 Black/Green is ground.

 

Not sure on numbering, but if I remember the color codes correctly, red/blue should be the start circuit to engage the solenoid (start position on ignition switch -> NSS -> solenoid "S" terminal).

Red/green is from run position on ignition switch, direct to ignition module and via resistor wire to coil + terminal.

Orange & purple wires to distributor are the two sides of the pickup coil for the reluctor that supplies the timing signal for the electronic ignition (the hall effect sensor that serves the function points did in older systems).


Switched power to an MSD box would be diode-isolated supply from both the red/blue and red/green wires (hot in both start & run) if it needs 12V all the time. If it can get by on ~7-9V during cranking, supplying it from the red wire at the Duraspark module would work. If it needs 12V, the white wire at the Duraspark module should tie into the red/blue wire anyhow, so you could build the diode-isolated circuit right there on the red wire/white wire connector.

 

Bypassing the resistor wire, by tying into the red/grn directly at the switch provides constant 12v supply once switched, correct?

 

Is there any chance that 734 orange/yellow and 735 purple/blue get the same signal from the same source at the same time so they get spliced to the same wire on the MSD?

Edit: duh, I'm going to look at the connector to see what links to what.

 

I'm trying to simplify the wiring diagram. This is not the finished product because I don't have the connections labled for the proper sides and I plan to color code the lines. In the end I am going to post what I figure out so other people can do this. But the goal is to use the OEM connections and wires as much as possible.

 

Is it safe to assume the "Batt" side of the coil is positive and the "Tach Test" side of the coil is negative?

 

Yes, tying into the red/green at the ignition switch would give you 12V in the run position. You'd still need to tie in the wire from the starter solenoid "I" terminal to get voltage in the start position.
No, the purple/blue wire and the orange/yellow wire are the two sides of the magnetic pickup coil. They'll go to the two mag pickup wires on the MSD box, whatever colors those are.
Yes, that's correct.

 

So the magnetic pickup wires DO get used. Is there a positive and negative pickup on the dizzy? IE, can I get them wired backwards or does it matter?

And thank you!