Looking for a momentary hot wire

[grandpaslincoln]

When you turn the ignition to "start".


At the moment I've only got a 9V resistor wire running to my ign. coil. This was all well and good during summer, but now that it is getting cold, the 9V makes for hard starting in the morning. I need that momentary 12V current during starting to provide a hotter spark. I found a wire on the ignition switch plug that provides 12V only when you are starting the car, but not sure where it runs to or what it does. It's a white wire with pink dots. Is there another wire somewhere that will get me the momentary 12V without relying on this wire? What I'm afraid of is feedback voltage from the 9V wire feeding whatever this wire on the ignition plug is feeding and causing a short or something somewhere.

[turbo2256b]

just get an MSD coil

[89GrandMarquis]

When you turn the ignition to "start".

How about the ignition key feed to the starter solenoid (on your fender well, next to your battery)?

[gadget73]

Use the I terminal on the starter relay. Thats what its for.

[89GrandMarquis]

Use the I terminal on the starter relay. Thats what its for.

Yeah, what he said.

[turbo2256b]

The S terminal is momentary. The I terminal is all ways hot with the key on I have used it to run fuel pumps and any number of other things as well as coils.

[gadget73]

Doesn't work that way on Ford relays. There isn't any way for the starter relay to keep a switched hot with the ignition anyway. Usually the only reason that would appear to stay hot is because its tied in with the ignition coil so it gets +12v during cranking. Ford ignition switches don't provide power to the ignition circuilt while cranking, and that I terminal on the starter relay is the way around that. Can't tap the ignition into the S terminal otherwise it will fry the ballast resistor. The relay will be pulling power through the ballast resistor trying to close and it'll smoke. You could run it off the S terminal with a diode but not really much point in getting fancy when there is a circuit designed for exactly this use already. Using the I terminal and the normal ignition coil power feed connected together is how I powered the MSD box in Nate's car, and it works. Couldn't make it start otherwise. Without the I terminal hooked up, the engine would catch and run when the key was released. With just the I terminal, it would die as soon as the key was released. Using both makes it start and run normally.

[grandpaslincoln]

Well, that didn't work.

Heres the problem. When you turn the key to "on", the coil is fed 9V via a resistor wire. Taking a 12V lead from the "+" side of the coil (the side that has the 9V lead) and putting it on the "S" terminal on the solenoid, automatically energizes the solenoid and starts the car. Even though it's just 9V, it's still enough to activate the solenoid. Putting the 12V lead right to the starter side of the solenoid puts 9V to the starter. Not enough to turn the starter over, but even while driving, the starter would get 9V constantly, which could cause damage to it or something. Anyway, that ain't gonna work, unless I get a 12V Diode and run it from the "S" terminal on the solenoid to the coil, so that voltage only goes one way and prevents the solenoid from energizing.

[gadget73]

Use the I terminal, it won't do that, unless you have one of those lame relays with only 1 terminal on it. Nate's 85 had and used both terminals tho so I'd imagine your 85 should have it.

[grandpaslincoln]

I don't see an "I" terminal, theres one that goes from the batt to the solenoid, and then everything else runs off that one, theres the "S" terminal with two red wires coming off, and then the other terminal runs from the solenoid to the starter.

[turbo2256b]

Not all solenoids have 4 terminals two big and two small. Mosst aftermarket ones do. Your car can use either.

[turbo2256b]

Once the key is in the on position the I terminal is always hot. The S treminal only operates when the key in in the start position it has no power in the on position.

[89GrandMarquis]

Well, that didn't work.

Heres the problem. When you turn the key to "on", the coil is fed 9V via a resistor wire. Taking a 12V lead from the "+" side of the coil (the side that has the 9V lead) and putting it on the "S" terminal on the solenoid, automatically energizes the solenoid and starts the car.

Based on this - I'd say you need a diode. That way, that current from the S terminal on the solenoid can go to the ignition, but not the other way around. RadioShack sells 6 ampere diodes for about $3 each.

Put the diode "in between" the solenoid and your ignition feed, and orient the diode so that the stripe is on the ignition side.

That'll do it.

P.S. I'd solder the connections if you can. Cover the diode up with tape, it'll be OK.

[turbo2256b]

Based on this - I'd say you need a diode. That way, that current from the S terminal on the solenoid can go to the ignition, but not the other way around. RadioShack sells 6 ampere diodes for about $3 each.

Put the diode "in between" the solenoid and your ignition feed, and orient the diode so that the stripe is on the ignition side.

That'll do it.

P.S. I'd solder the connections if you can. Cover the diode up with tape, it'll be OK.

Ditto on the diode. If your hooking it to a hot wire in the run position you wont want current going back to the S terminal.

[grandpaslincoln]

I could also use a relay instead of a diode, although the diode would be cheaper. But relays are cool lol