I bet you still get 10v with the relay. That's the drop caused by the starter. You can test this theory by measuring the voltage at your planned spot to put the relay tap, and see if it is higher, or 10v there also during cranking.

 

I'll bet you're right....

 

I am powering the relay straight from the battery, just to clarify, the alternator power wire was just to switch the relay on when key is in the "on" position.

I was just using the relay to power the dizzy and it would not start till after i stopped cranking. After hooking up the "I" wire it will start after about a 1/2 crank.

I hope I am making sense....

As for the dizzy, I had to stab it a few times to get the fit I wanted to where I had the most timing adjustment, i also bought a set of universal wires that you cut to fit your application, that made it easy.

 

I was wondering about the drop during cranking. That makes sense. Running from the I terminal will give it battery plus alternator so the full 12v

In re-reading the instructions they do say full alternator voltage and their FAQ says to connect it via the starter solenoid.

So, if my feeble mind is recalling correctly (thinking back to my 68 Cougar I had in 1978), the I connection on the starter solenoid provides full 12v only when cranking. When the engine is running, it provides nothing, so the coil will need its power once it's running from another source, normally through the connection from the ignition switch via a ballast resistor.

In my case, that connection is on the 'round 4 wire plug' on the driver inner fender. I planned to use that to trigger the relay, but I'm thinking since that does not have a ballast resistor and provides 12v at key on; why not forgo the relay?

I could just connect the I and the old coil hot (the one on the connector) to the coil. The I connection compensates for the voltage drop during cranking. If I'm remembering right, that was the original design more or less?

I think I'll go out and do some testing with the old voltmeter to check my theory; I'm pretty sure that is how the original design was and I can forgo the relay.

I'll post my findings shortly.. (shortly being a relative term)

 

This is a diagram I made in paint for you, this is exactly how mine is wired, and I have zero issues. The run wire from the key to the voltage regulator is the red/green wire I tapped into for the relay switch. But any 12v run only source will do. Hope this helps

 

That's what I was saying; what is the purpose of the relay?

Your KEY ON Power triggers the relay to provide 12v battery power. The connection I was considering to use to trigger the relay, is 12v. So why not just connect that to the DUI Coil, in addition to the I connection?

Would it not have the same effect?

WITH RELAY: I connection to coil direct. 12v via relay triggered by RUN (KEY ON). 12v provided by battery via relay, only when RUN (KEY ON).

WITHOUT RELAY: I connection to coil direct. 12v via KEY ON power, only present when key in RUN position.

What's the purpose of the relay in this case? I can understand if there is no good source of 12v at key on (RUN), but if there is I don't see the need for the relay.

Am i missing something here? Perhaps the KEY ON power varies while the battery doesn't? (don't think so but I've been wrong before).

 

I went with the relay to assure a constant 12v to the dizzy coil. I reckon you don't have to use a relay, but I didn't want to mess anything up with the factory wiring, so I added it.

 

Makes sense. In my case, using that plug pretty much just duplicates the factory wiring. I'll give it a try and if all else fails, go to the relay method.

THANKS!

 

Well, as should have been expected, my truck threw me a curve. I planned to do as others have suggested and use the I terminal off the starter solenoid. Only one issue.

My solenoid does not have an I Terminal! It is labeled, but sealed off, no connector.

I also got to thinking about this (never a good sign)

The starter solenoid is a just a relay. The input to the relay is the battery power. The S connection is the trigger for the relay and when ON (Start Position) the relay transfers it's input voltage (from the battery) to the starter and to the I (Ignition Connection) terminal on the relay. Pretty basic.

Given that the battery voltage drops during cranking, to about 10v, the voltage at the I terminal would also be 10v. From my experience, the starter motor is a pretty big draw and dropping a couple volts at cranking is most likely normal.

In a points system, it needed 12v at cranking (10v with drop) and then less during run condition (the purpose of the second resistance wire). So in a points system, when cranking we get 12v +/- and then when the ignition switch is moved from start to run, the I terminal loses power and the KEY ON power, via the ballast resistor, provides the lower voltage power to the coil. In that system you want that so the coil doesn't burn up. Make Sense?

In a TFI system, as mine had, it didn't use a ballast resistor and provided 12v via the KEY ON power. That would be the reason I don't have an "I" connector on my relay - my old system didn't need it as it had 12v all the time.

So, if my logic is sound; 10v drop at cranking is normal and should be OK. The KEY ON power is the full 12v (10v when cranking, same as the I terminal would be) and should be able to power the distributor. No relay, no complications. That's the theory..

If my theory is off; how so?

Thoughts anyone?

 

Your truck was wired for several different engines. You were using the TFI type wiring that took full voltage to the coil, you had a square coil correct? That system uses full voltage from the white/blue wire.

Your truck also has the wiring for a duraspark II system. This is the regular non-computer controlled ignition box that the earlier sixes used, and the 302's used till 85 when they went efi, and the 351w's and 460's used this system till 87 or so. This system uses the resistance wire to feed the coil, the red/green one. If you hunt around a little bit you can probably find it somewhere under the hood. This system needed a resistor bypass for starting. They fed the coil a full 12v during cranking, and then fed it about 9v through the resistor after the engine started. The old points system used the same resistor bypass setup.

There are two ways they bypassed the resistor. In the older trucks they used a solenoid with the extra "i" terminal to feed the coil a full 12v during cranking only. Sometime later they quit using the solenoid with the "i" terminal, and instead had a extra contact in the ignition switch to bypass the resistor which is in the harness near the ignition switch.

What I would do if I were you is just use the white/blue wire(or blue/white, whatever it is). Get it running, and measure the voltage at the coil. If you get a voltage drop there compared to what you have over at the solenoid, you can remedy that by using a relay, and trigger the relay with the white/blue blue/white wire. You will probably get a volt or or so difference.

 

Yep. That is what I thought and what I'll do.

There is a 4-wire connector on the driver fender that has connections to the temp and oil gauge, as well as 12v KEY ON power that went to the old square coil via the old harness.

I already isolated that connector from the old harness and am using that to keep my gauges connected. I cut the other two (leaving pigtails) so I could remove the rest of the harness. One of those pigtails has 12v KEY ON power.

My thought is to connect the HEI coil to that KEY ON source pigtail. If it works, it will keep things simple and factory looking; no extra relays or complications. I already checked that source and it is a constant 12v (ok, 10v when cranking) with KEY ON or in START. Should be good to go

That's the theory anyway..

 

Sounds like you have a good understanding of what you are doing. Having a DUI dizzy is not going to look factory, so I don't know why you are avoiding a little 1" square relay mounted to your fender wall that you can add a totally new circuit for and make it look like its supposed to be there. You are going to have to splice into the factory wiring no matter which way you do it. Mine looks clean, and you can't even tell it is there.

What are you doing with all the factory emission stuff that is just going to be "laying" around under the hood?

By going to DUI system, you would have to make a whole new harness to make it all look factory, but that is just my $.02

And I would recommend going and picking up a starter solenoid with the "I" terminal on it, or you will have starting issues......

 

Pull the red/blue wire off the solenoid to keep the starter from running, this should prevent the voltage drop you see in START. This is just a way to verify 12V with the key in START.

 

I understand what you are saying
My connection to the DUI coil will be made using the
factory connector in the existing harness, the pigtail splice will look like its part of the harness.

The smog pump is gone and you can't tell it was ever there

The Evap and EGR were converted to vacuum control via
A ported vacuum switch instead of the computer and selenoids

If my key on power provides the same power as the I connector from the starter relay, why do I want that connection?

I'm fine with it, just don't want to go there without understanding why

 

I tried first to just run a factory 12v hot in run to the coil, and it dropped off while cranking. That is why I ran 12v directly from the battery via a relay switch. If you can get it to work without a relay, then by all means do that. Just trying to save you some work possibly.