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Old 05-28-2008, 12:00 PM
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Ford starter solenoid/relay

I'm confused

I'm in the process of (FINALLY) wiring my AVATAR car. There is one area that concerns me - I'm, according to the SVT mini starter instruction sheet, required to use a "firewall solenoid" - or am I in a terminology glitch, with all of the Fords having a firewall solenoid. Since I've never had the "pleasure" of this newer design am a little bit hesitant to just bolt it in place and have at it. I've attached the Ford wire up page with my soleniod drawn in for some discussion and maybe a sketch (Doc - where are you when I need you??). I'm fairly sure of how it goes, but a wrong connection spells $$$$

Quite frankly - I think the Ford sketch is wrong (or I have the wrong solenoid).

My interpretation - the battery cable should be connected to the 'B' term, the starter cable to the 'M' term, the motor solenoid to the 'S' term and the ignition wire to the 'I' term

Dave W


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Old 05-28-2008, 12:26 PM
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My grandfather had a '95 F-150 with that type of newer Ford solonoid, as did my '94 Tempo. I never could figure out how they were wired.. I don't see why you could'nt use a regular Ford solonoid. B to battery cable, A powers the starter main power cable. put solonoid power on the Start terminal. Ignition terminal can be left alone unless your using points
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Old 05-28-2008, 12:56 PM
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Quote:
Originally Posted by Irelands child
I'm confused

I'm in the process of (FINALLY) wiring my AVATAR car. There is one area that concerns me - I'm, according to the SVT mini starter instruction sheet, required to use a "firewall solenoid" - or am I in a terminology glitch, with all of the Fords having a firewall solenoid. Since I've never had the "pleasure" of this newer design am a little bit hesitant to just bolt it in place and have at it. I've attached the Ford wire up page with my soleniod drawn in for some discussion and maybe a sketch (Doc - where are you when I need you??). I'm fairly sure of how it goes, but a wrong connection spells $$$$

Quite frankly - I think the Ford sketch is wrong (or I have the wrong solenoid).

My interpretation - the battery cable should be connected to the 'B' term, the starter cable to the 'M' term, the motor solenoid to the 'S' term and the ignition wire to the 'I' term

Dave W

The Ford sketch is correct. The term "solenoid" is often used incorrectly here. The can on the mini starter is a solenoid. It's purpose is to use electromagnetic force to mechanically move the starter drive out against the ring gear on the flywheel. This is the design GM starters have used for decades. Older Ford starters did not use this design. Instead they were configured so that centrifugal force from the starter motor turning drove the starter drive outward against the ring gear.

The thing on the firewall, while called a "solenoid" is actually a relay since it only switches electrical current. The old-style Ford solenoid simply sent battery current directly to the starter motor windings, which spun and flung the starter drive outward. The mini starter works like a GM starter, in that battery current is applied to the solenoid on the starter at all times (as the sketch shows, the battery cable is wired to terminal B on the firewall solenoid and thus to the upper terminal on the starter-mounted solenoid). The small terminal on the starter-mounted solenoid requires a 12V signal (usually from the START position on the ignition switch) that energizes this solenoid to both drive the starter drive outward and to close the contacts that send high current to the starter motor windings.

From what I can make out in the instructions, the use of the firewall-mounted solenoid is simply because it is already there. It really doesn't add anything to the circuit, it's simply an extra "switch" between the ignition switch and the S terminal on the starter motor solenoid. You could get the same effect by connecting the battery cable directly to the upper post on the starter-mounted solenoid and connecting the wire that normally runs to the S terminal on the firewall solenoid to the S terminal on the starter mounted solenoid instead. Of course, at that point it would be wired like a GM.

The only reason to use the wiring shown in the instruction sheet is that there may be other circuits connected to the firewall mounted solenoid.
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Old 05-28-2008, 02:20 PM
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Thanks Joe - that makes sense. While I've had Fords forever, just hadn't run into a situation where I've had to replace either a solenoid or starter since they went to the GM kind of system. It appears that I need the "firewall solenoid" for is to be only a transfer and hook up point for battery and starter cables with an ignition switch actuation. Someone got some 'atta boys for that design as well as the yokel who wrote the ministarter instruction. I'd wipe those out with an 'aw sh17' if I was their boss.

Dave W
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Old 05-28-2008, 02:49 PM
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Why? "Because that's the way we've always done it"

Actually, some of their engines may use the old style starter, so it may be cheaper and easier to leave the firewall-mounted relay... er, solenoid, in place for all applications.
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Old 05-28-2008, 06:15 PM
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Might also be noted that this is the same as a GM 'hot start' fix.

So, when the car is hot, there will not be the voltage loss in the starter solenoid.

Instead of using the starter/solenoid internal connections to 'fire' the starter, all of the switching is done with the relay mounted remotely.
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Old 05-29-2008, 07:46 AM
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Quote:
Originally Posted by Bryan59EC
Might also be noted that this is the same as a GM 'hot start' fix.

So, when the car is hot, there will not be the voltage loss in the starter solenoid.

Instead of using the starter/solenoid internal connections to 'fire' the starter, all of the switching is done with the relay mounted remotely.
That's what I thought at first, but unfortunately it's not. Look again and you'll see that they show a 12 gauge wire going from the firewall relay to the 4 mm terminal on the starter-mounted solenoid. That's only the S terminal that would normally be the wire from the ignition switch on a normal GM setup. In order to accomplish the "hot start" fix you'd need to run a heavy gauge battery cable directly to the large lower terminal on the starter-mounted solenoid. That's the terminal that connects directly to the motor windings. As shown in the Ford instructions, the current to the motor windings still gets switched by the starter-mounted solenoid.
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Old 05-29-2008, 08:28 AM
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Looks like these mini starters are not in common use on street rods !!!!

This is what I've written to myself for future reference:

"First of all, the Ford instruction is correct, but poorly written. The existing starting solenoid actually becomes a relay, that the actual solenoid for the Ford mini-starter is now built into the starting motor itself.

From here on, I'll just call that existing solenoid a relay.

The relay must be grounded and supposedly the mounting bracket is that ground according to the Ford instruction

Per the Ford instruction - the battery cable and the starter cable(supplied by Ford) are landed on the same terminal (B) of the relay. The #12 wire (also supplied by Ford) lands on the other large terminal of the relay (A) and are connected to the starter motor terminals as shown in the Ford instruction

The relay has 2 smaller terminals - the actuating wire (from the ign switch) terminates on the 'S' terminal.

The ' I' terminal appears to be a hot terminal for other uses - and in my case, possibly the power source for my MSD control box "

Joe - anything that you can see that I missed??

Dave W
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Old 05-29-2008, 09:03 AM
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Quote:
Originally Posted by Irelands child
Joe - anything that you can see that I missed??

Dave W
By george, I think he's got it!
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Old 05-29-2008, 09:09 AM
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HOOOOOOORAAAAAAAAAY for our side .


Thanks for the help.


Dave W
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Old 05-29-2008, 09:44 AM
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When I wired the MSD box in my Falcon I used the I terminal for power to the switch side of a relay, ran power direct from the batt for the MSD box.
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Old 05-30-2008, 12:18 AM
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HOOOOOOORAAAAAAAAAY for our side .


Thanks for the help.


Dave W
I got my mini-starter from DB electrical the diagram is the same as the Ford,WOW does that baby spin!
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Old 05-30-2008, 07:14 AM
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Boats too

I work on some boats with a Ford 351 engine. They use this system also. It is fine until some bonehead thinks the relay is the "solenoid" for the starter.
The old style Ford starter had a movable core on one of the field windings of the starter motor, and when the starter was energized, the magnetic field created pulled the movable core into the starter windings. There was a linkage that moved the starter pinion into the flywheel.
Newer Ford starters have permanent magnet starters, and gear reduction, and use a GM style solenoid to move the pinion gear.
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