I am out of my depth and could really use some help. 78' 250 that I got over zealous with and added a 3g alternator, MSD ignition (replaced a 20 yr old Mallory), MSD Blaster 2 (replaced a 20 yr old blaster), MSD dizzy, and then hit some electrical struggles.... Changed out the starter relay, the starter, ignition switch, battery and not have the issue of the starter staying engaged even after removing the key. When this has happens I had to pull the neg. terminal off of the batt to shut it down. With the neg. terminal pulled I still had 12v on both sides of the starter relay. Then removed the I and S terminal leads and still had power to both sides, removed the ignition switch and still had power, removed the lead to the starter and had about 3 seconds of power (lower voltage using an idiot light here) until the charge cleared. At this point no power reading on the switch side of the starter relay. Reconnect the starter lead and all is normal until I start the whole process again.

Cleaned up the batt neg to engine block ground and reconnected grasping at straws....

 

Spunds like bad relay. I know its new but power across it while everything unhooked tells me its faulty and sticking.

 

X2 on the relay - I had a suspect one (that wasn't very old), once in a blue moon I'd walk by my truck and the oil light would be ON (key in my pocket). Swapped out the relay and all good.

btw: I paid a couple xtra bucks and got a Motorcraft new one instead of a knockoff.

 

OK, two votes for a bad new relay. I'll swap that out. Any thoughts on why the starter power lead would have charge after being pulled from the relay?

 

Perhaps a capacitor in an accessory. Or maybe the MSD box is connected wrong - I had that happen, but with a Ford Duraspark system I put in a '68 Cougar.

The cause was that I had connected the Duraspark's 'cranking power 12V+ input' to the red wire which goes to the "S" post on the solenoid/starter relay.

That wire is supposed to go to the "I" post on the solenoid, because the solenoid contains a diode, which prevents current from back-flowing, and causing the solenoid to stick its secondary contacts closed, making the starter run away. Once I moved that wire to the "I" post, the starter run-away stopped.

MSDs are said to be modeled after the Duraspark system, so they probably have two 12V+ inputs.

The starter run-away condition my truck had when I got it, was due to that missing groundstrap between the engine and the body.

 

I like to say that is what you get for getting "over zealous with and added a 3g alternator and adding ect..." and all the other stuff. But that does not help your situation. With a stuck on starter, key off or out I would say YES you have a stuck on/welded on contacts of the starter solenoid (the one mounted to the passenger side of the inner fenderwell), new or not it needs replaced. Some times when they stick you can tap on them with a pair of pliers, but pulling the pos battery connection or the small I or S wire connection wide should of done the trick. Also double/triple check all the wiring routing for the upgrades.

 

Ok, fellas I totally respect and appreciate the replys. THANK YOU VERY VERY MUCH! Especially like 77&79's fatherly reply. I know, I know but I have owned this truck for over 25 years and we have become familiar with one another. Part of the reason for all of the changes is I was moving from the Mallory which was giving me struggles to the MSD and noted a parasitic draw of the alternator that lead to the need for an alternator replacement so of course I went for the cool kid one of the 3g. The starter replacement was a rule out and when I pulled it I had some beat up teeth so I took the easy road and replaced it. Basically the catalyst of my latest endeavor was a tune up replacing a hit and miss Mallory ignition and way over due for for cap, rotor, wires replacement. So.......

Today purchased a new starter relay based on the homies replies (3rd one) which I did not get enough "shop time" to install and check (I am married... lol).

My next question is to clarify the S and I connections on the relay. Brown, blue/red wires to determine with my changes which ones I still use.

When I finally get through this I will be coaching others like 77&79 to take on one issue at a time. OR I will get completely frustrated and completely rewire the whole truck!!!!!!!!

 

On the MSD front, I have a question to anyone who knows these things that I hooked the batt up then pulled the +side from the batt then jumped from -neg batt to the power wire of the MDS showed 10v which slowly dropped off to 0 over about 5 min. Is back feeding + from an MDS 6AL normal?

 

I've never messed with an MSD. Can you get any troubleshooting info for it? It's a capacitive discharge system, and the decaying voltage could be from a capacitor, but I don't know.

Here's what I know about Ford ignition power: When you crank the starter, the ignition puts out a full 12 volts to the coil to aid startup. But when you release the ignition key to Run, the coil gets stepped down to something like 6 to 9 volts, to keep from overheating the coil.

With the original Duraspark ignition, you want the 'Run' wire from the ignition switch powering the Run input on the box, or however Ford did it.
There is a second input for the 12 volt to the coil while cranking, and that one should go to the I post, so you get the benefit of that diode I mentioned before.

Now of course, all bets are off when using aftermarket parts, so read the instructions till they all make sense - usually takes multiple times for me with something like that, and it's even better if I start reading them days before attempting the job... It probably hooks up the same as a Duraspark, but that's why you read the instructions, to be sure. I've read that MSD makes adaptor kits, so you can be mostly, or maybe even entirely, plug-and-play when installing it. I've also read that the cheaper MSD boxes can be troublesome.

If you haven't thrown out the Mallory, you might give it a try with new plugs, wires, and cap & rotor, and see if it clears up. I think I'd have more faith in a 20 year old Mallory than in many things made today and recently.

With electrical, it's best to make one change at a time, and testing and ensuring that it's correct, before moving onto a different part/component. That holds true for anything you work on.

 

Ok. All ya all were correct, THANK YOU!!! 77&79 yes! I was foolish to deal with multiple components at the same time!! I mean like way more hours of testing and back tracking than necessary. Mean Green, yep that capacitor is a feature of the components combo I have. Kegger and & 77 HOS went back to the parts store (did not have a Motorcraft) and picked up the $30 version of the $20 relay which was noticeably heaver in the hand and swapped it out. All that to say I am back up and running!

I now have new questions. LOL
1) How does a fella measure the output of a 3g alternator?

2) I have seen several posts on what the timing should be set at (460). How does a guy set it by ear, then set it to his particular engine/carb/ignition/etc combo without pulling it and putting it on the dyno?