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8 on the msd box violet wire is + and on the ford harness the orange wire is positive coming from the dizzy. If you pull up MSD's install instructions page 18 has a diagram.
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.
32 Red/Blue is not GROUND! It is 12volts to the starter relay (Via NSS switch). Use at least one diode on this wire if your going to tie it with another, like 732 White.
16 red/green is similar to 732 white in that it gets power in ignition switch run. However it goes through a resistor wire and then the ignition coil +. The "I" Terminal also goes to the ignition coil + to supply full voltage at start.
I would use the old Ignition Module Connector, and splice in the fuse and diodes. Then it'll be similar to how the factory did it. And can revert back to stock if need be by simply carrying around a stock ignition module.
734 Orange/Yellow and 735 Purple/Blue are the reluctor and not sure if they are negative/positive or AC, and 733 Black/Green is Distributor 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.
16 Red/Green Doesn't touch the Ignition Module at all and goes to the ignition coil through a resistor wire.
16 Red/Green could be used, but I would worry about the resistor wire (burnt one up almost taking out mah truck). If using 16 Red/Green, unwrap the harness and replace the resistor wire (From near the fuse panel to around middle of dash) with 14 gauge wire and use an inline fuse.
I would keep it simple and not use 16 red/green and only the two wires to the Ignition Module (32 red/blue and 732 White). Then the rest of the harness can remain stock and un-altered.
And yes, use the diode on 32 Red/Blue at the very least! don't want to send continous power to the start relay/solenoid...
16 Red/Green Doesn't touch the Ignition Module at all and goes to the ignition coil through a resistor wire.
Thanks, couldn't remember if there was a green trace on the wire to the module or not. Either way, ignition switch run position feeds the coil via a resistor wire and the ignition module directly. Former has the green trace; latter doesn't I guess. Definitely wouldn't want to run anything but the coil off the resistor wire.
Haha, Funny story about running stuff off the resistor wire! I was switching to EFI and had an electric pump at one point, and wired it to the Coil! Later wondered where the burning smell came from and eventually took the pump off it. And then had a weird electrical failure after the EFI, and that wire got burnt up! Or very close to burning... Lucky me it didn't melt the other wires in the harness and I swapped it out for a 14 Guage wire and installed an inline 10 A fuse. Bleh, learning about the resistor wire the hard way!
And yeah, the White (732) wire does the same as the Red/Green before the resistor. But I'm looking at the 78-79 schematics, and there might be differences to the earlier trucks... Concept is still the same, stuff two diodes to tell the MSD to power on (or relay for EFI like I did).
Last edited by ZarK-eh; Jul 14, 2015 at 01:42 PM.
Reason: words being words...
So I did this. You'll see the diodes near the MSD, the 3 amp Fuses in line and the splices close to the harness. Notice the white wire from the MSD is tucked back in since I'm not using it:
That leaves me with three wires from the distributor to hook up, but there are 4 wires left coming from the OEM ignition module:
You can pull the wires right out of that blue clamp from the OEM ignition module. I know one goes to the black wire from the MSD and I labeled it. But now I have three wires coming from the distributor and only two wires coming from the MSD (if I don't use the white wire from the MSD), the green - (which goes to the purple wire in the harness) and violet + (which goes to the orange wire in the harness). It looks as if I have nothing to ground out the dizzy because I see nothing coming from the MSD to hook to the black wire from the distributor. Should I just make it go to a ground that I create? What do I do with the black wire?
I have one other concern. It has been a few weeks since I soldered these diodes. From the picture I wonder if I separated the diodes on the split side or if they can touch or maybe a spark could jump the gap. If so, is that a problem?
The Diodes on the split side should not touch at all. If they do, you could send power to the starter relay/solenoid causing it to engage with the engine running... Pull the heat shrink tubing and separate them better. The Diodes are to prevent power from passing from one circuit to another and shorting them out kinda defeats it's purpose. Also looks like you have the polarity correct (that white band on one end) .
As for the 3 wires on distributor and 4 wires on OEM Ignition Box and what the MSD has... *whew*
Two wires on distributor are the Mag pickups which do go to the MSD, the third wire is Ground. Not sure if it needs to be grounded, but better safe to ground it. According to my '78 wire diagrams, the Black/Green wire is ground. I would ground it where the MSD is grounded or other convenient spot. Orange/Yellow and Purple to the MSD pickups seem right.
You should be able to do continuity checks on these three distributor wires. Should be continuity between the pickup wires, but not to ground. The Ground wire should have continuity to the distributor house, but not to the pickup wires.
The OEM Ignition has one wire going to the Ignition Coil, while the MSD has two. The other wire on the OEM setup Ignition coil goes to the 'I' terminal on the starter relay/solenoid and to a resistor wire and then the ignition switch. Use only the MSD coil wiring! Leave the other wires unused and protected (Wrapped and heat shrink) or cut at the oem plug.
Looks like your very close to starting the engine!
Did some more work today. It's not cleaned up yet, of course, so it looks like a plate of spaghetti right now, but here it is:
Originally Posted by ZarK-eh
The Diodes on the split side should not touch at all.
I pulled off a lot of the very outside heatshrink. I had separated them properly. I should have trusted myself, but better safe than sorry. Now they are wrapped all together with waterproof tape I use on my ham radio antenna wires. It bonds to itself and turned into a heavy rubber coating. Very nice stuff.
The OEM Ignition has one wire going to the Ignition Coil, while the MSD has two. * * * Use only the MSD coil wiring! Leave the other wires unused and protected (Wrapped and heat shrink) or cut at the oem plug.
So, are you saying that the Red OEM wire (at the top of the picture labeled "To Coil" wrapped into a loop) coming from the square connector coming from the firewall does NOT go to the coil; instead the Orange wire (at the bottom of the picture labeled "To Coil") is the one that gets attached to the coil? And I should remove the Red OEM wire from the square connector? That is easy enough to do, but that means that there will be a wire coming from the firewall that goes nowhere. Is that cool? Do I need to remove it from inside the cabin as well? Also, see the green wire in the loom that goes to the dizzy; I have not soldered that to the black wire from the MSD, but they are tied together for the picture.
The other wire on the OEM setup Ignition coil goes to the 'I' terminal on the starter relay/solenoid and to a resistor wire and then the ignition switch.
Ok, I'm a little lost on this one for a minute. I will come back to this.
Did some more work today. It's not cleaned up yet, of course, so it looks like a plate of spaghetti right now, but here it is:
I pulled off a lot of the very outside heatshrink. I had separated them properly. I should have trusted myself, but better safe than sorry. Now they are wrapped all together with waterproof tape I use on my ham radio antenna wires. It bonds to itself and turned into a heavy rubber coating. Very nice stuff.
So, are you saying that the Red OEM wire (at the top of the picture labeled "To Coil" wrapped into a loop) coming from the square connector coming from the firewall does NOT go to the coil; instead the Orange wire (at the bottom of the picture labeled "To Coil") is the one that gets attached to the coil? And I should remove the Red OEM wire from the square connector? That is easy enough to do, but that means that there will be a wire coming from the firewall that goes nowhere. Is that cool? Do I need to remove it from inside the cabin as well? Also, see the green wire in the loom that goes to the dizzy; I have not soldered that to the black wire from the MSD, but they are tied together for the picture.
Ok, I'm a little lost on this one for a minute. I will come back to this.
From what I understand, yes the wire from the square can be pulled and go nowhere. It is the same wire that heads to the I terminal on the starter solenoid/relay, and is also fed from ignition switch through a resistor wire. You can check for continuity to be certain to that I terminal. This isn't that important, and included it as an FYI.
I would pull the wire from the square block and leave it blank or stuffed with white lithium grease for corrosion protection. I would leave the cab wiring in place to leave this truck stock, and in case the OEM is installed.
That green wire is for the distributor pickup or trigger?
