Starter relay question.

[Fox]

What are the two front post for?

I am doing the wiring of my run stand and am a little puzzled.
My engine related books don't address the starter relay other than naming it and the electrical books only tell me how one works.

It is an early 70's relay for a Ford 302.

Thanks for the insight.

-John

[G.R.]

Tell me that isn't a Battery ground cable(black) hooked up under the battery positive(red)cable on the positive side of the relay. If it is you'll have a direct short back to the battery as well as blowing out the relay, and a possible explosive situation. I hope I'm wrong.

Positive battery should be on the large left post, Neg on the large right post. small right post would be for ignition and alt, small left is ground. At least that is how mine is wired though it is of an earlier style and design.

[computerworks]

...putting +12v on the "S" terminal will close the relay and connect (short) the two large posts together.

[Excaliber]

Now I'm confused!

Big terminal on the left is direct battery PLUS cable. It is generally THE connection that ALL other wires get their power from. Main power TO the "fuse block" for instance would come from a smaller wire attached to the BIG left terminal/postive battery cable connection. That way the "fuse block" ALWAYS has power direct from the battery.

The right side OTHER BIG terminal gets a large wire from it directly to the started terminal. When the solenoid (switch) closes it connects the left side (direct battery plus power) to the right side which feed direct PLUS battery power to the starter.

SO, how do you turn on the switch (solenoid)? By applying 12 volts PLUS power to one of the small terminals in the front. I do blieve as Ron has said it is the "S" terminal.

The OTHER small terminal RECEIVES 12 volt power ONLY WHEN AND DURING THE ACTUALL TIME THE SOLENOID IS "ON". In other words, only when the starter is actually cranking. Otherwise there is NO POWER at the second terminal at all. So WHAT would a guy use that terminal for?

It's kind "old school" and goes back to the days of "point type" ignition systems. When the starter is engaged it draws a tremendous amount of power from the battery. Typically dropping available voltage from 12 or 13 down to 10 or so.

IF it drops below 9.6 volts good chance your battery is bad. Anyway, the old point type systems (and SOME new electronic units) will BURN UP if you put 12 or more volts to them. So they get powered through a resistor, which drops battery voltage from 12-13 down to 7-8 volts (some say 6).

Now during CRANKING (starter spinning) and battery voltage dropping due to the big load, and the resistor ALSO dropping the now LOW voltage to the coil even lower there is no power left to FIRE the coil. The coil, during cranking may only be getting 4 or 5 volts, perhaps less. SO, the SECOND SOLENOID TERMINAL provides a temporary BY PASS around the coil resistor and puts ALL AVAILABLE voltage directly to the points/electronic ignition/coil (which would be about 10 volts). THUS providing a HOT spark during the cranking phase.

Think of it this way: BOTH the big and small terminals on the right receive battery power ONLY when the solenoid is actually engaged. The two terminals do different jobs, one for the starter (big guy) and one for the ignition/coil/points (little guy).

...class dismissed.

Ernie

[Fox]

On the left: The red cable is + from the battery...The black, hooded red is going to the + starter solinoid terminal.
The cable colors are confusing but that is what came with the FRPP starter and how it is labled in the instructions.

On the right: The 12 ga black goes to the outer "blade terminal" of the solinoid. Is that correct? GR, are you saying that the large right post is -/ground?

Since this is mounted on wood and not the engine compartment, I grounded it in the upper right corner ( red 12. ga).

In my Summit ignition switch/starter button instructions it sends a wire to the battery, one to the ignition (the MSD, right?) and the last to the starter.
Should that "starter wire" (of the switch) go to the S terminal of the relay?

Thank you very much Ernie...This sh!t can give me a headache, but you example was very...Slick.

I appreciate any help...in physics I could play golf with a bb gun...but right hand rule/black box electrical always had me lost.

-John

[sharpe 1]

The starter relay is nothing more than an on/off switch between the battery and the starter.The positive cable from the battery goes to the large terminal on the side of the relay(battery) and the large terminal on the other side connects to the starter.The small connectors on the front are the controllers for the relay.You can use a 9 volt battery to activate them and make the relay work. The small terminals, one hooks to the ign. switch and the other to ground.When you colse the ign. switch it gives a ground to the magnetic coil.This closes the relay and power flows to the starter motor. HOPE THIS HELPS///

[sharpe 1]

The picture shows a direct connection between the battery and the starter. One cable goes on one side and one on the other.

[Excaliber]

G.R. touched on this with his post.

None of the four terminals in question are "ground". Only the metal case of the solenoid is to be grounded. On many applications only ONE of the small terminals is used, the S terminal to make the solenoid "turn on". The other small terminal is entirely optional depending on the type of ignition system you have.

Again, NO terminals on the solenoid are to be grounded in ANY way.

[Fox]

Thanks for the grounding point. As I said, I did make a effort to ground the relay, but not using a terminal, I grounded the mount.

I sense that it is still not hooked up right at the main terminals. There are two wires going to the solonoid, on either side of the relay??? In the picture it is the red hooded black cable to the + post and on the right side it is the black 12 ga. going to the 'blade terminal'. I will review the directions from Ford and will likely post for a clarification tonight.

I am sure you are all just stirring with anticipation...but I thank you for your patience and helping me clear this up.

-John

[Jack21]

Good lesson Excaliber.

Grounding. The starter solenoid case needs to be grounded, or it won't work. On a steel bodied car, it is almost a non-issue, until the mounting screws become corroded.

On a fiberglass car, or piece of wood, the case needs to be grounded, typically using a black, not red wire.

As stated above, the large connecters are used to power the starter through the solenoid (another name for a relay). The always hot side that goes to the battery is (or can be) used for an electrical pickup terminal for the rest of the electrical system.

The small terminal (marked "S" I think), powers the solenoid from the ignition Start switch terminal. A simple test for this is to touch a hot wire to this terminal while the case is grounded. The solenoid will "click", and on the other terminal, nothing will happen.

Also, as stated above, the second small terminal is ONLY used on older ignition systems that used ballast resistors in series with the ignition coil circuit. Electronic and CD ignitions do not use this start-only feature, as they run on full battery (or system) voltage all the time.

On the photo above: One large terminal (either one) should go to the battery. All other always hot system connections can be made here. The other large terminal gets connected to the starter only. The small terminal connects to ignition switch (or button) start. Nothing at the other small terminal. Ground lead coming off the solenoid case should be black to avoid confusion.

[RichBurroughs]

I am a visual person...maybe this will help.

[Fox]

Thank you all for the written and visual explanation of wiring the starter relay. Where were you all the night before the final?...

I have a good handle on how the relay and starter are to be wired but the diagram below still has me a bit puzzled.

1. Why two wires/cable to the starter if all you need is a positive and the ground of the housing on the engine plate?
2. Why is there a wire/cable to the starter on each side of the relay?





What do you think?

-John

[cobra427mnsi]

Fox

That picture must be of an older style starter. The "starter motor solenoid", in your picture, mounted to the top of the starter, is the same as the solenoid that is mounted to the plywood. They are the same thing. You have two starter solenoids there. I'm not sure what that "strater relay terminal" is ( I think they spelled it wrong).

You need to look at your starter itself. There should only be one large connection to turn over the starter. The circuit is completed because the starter body is grounded to the engine through the mounting bolts. RichBurrough's picture has the labels correct.

A starter solenoid is just a big switch (relay). the largest posts are used to start the car. One of them goes to the red terminal of the battery (doesn't matter which one). The other goes to the big terminal on the starter ( the only terminal on the starter). Use a heavy guage wire for both. The "big switch" starter solenoid is closed by running a smaller guage wire (12 guage or 14 guage) wire from the ignition switch to the "S" terminal on the solenoid. The other "I" terminal need not be used (depends on what ignition system you are using). When you turn the key to start, the "S" terminal wire excites the solenoid by closing the internal high amperage switch, thus sending juice to the starter. When you release the key from the start position the juice running to the "S" terminal is cut off and the solenoid high amp switch is opened cutting off power to the starter. Elementary my dear Watson.

There is a standard color code used for wiring.
Black = ground
red = 12 volts always hot
white = 12 volts switched

Hope this helps (not too confusing)

Paul

[Excaliber]

I don't know where the diagram came from but it is certainly misleading and NON STANDARD for any application I can think of.

It shows a FORD stlye solenoid at the top and a GM style solenoid on the starter.

Typical Ford starter does NOT have a solenoid on the starter. Virtually EVERY GM product DOES have a solenoid on the starter. Either way works, using BOTH ways also can work, but sure makes life complicated! Use one or the other please!

[Fox]

The Ford starter I have has the solenoid just above the starter motor as shown in the lower portion of the drawing.

Needless to say this is all very clear now. I will chuck the instructions and go with the principles we talked about above.

Positive battery cable to the starter. Ignition switch wire to the S-terminal equivalent on the solenoid and the ground is maintained by the starter housing secured to the engine/transmission plate.

What would I have done without CC...very likely some damage.

-John

[SVMCOBRA]

Fox, I am using the same setup on my Shell Valley with a 351W.
The big left post is for the battery and power to your fuse box. The big right post will have have two wires, 1 big cable to the starter and 1 smaller gauge to the solenoid. The small post on the left goes to the ignition switch and you have to ground the solenoid bracket. I do not use the small right post because I am using an MSD ignition system

Ray Hedden

[SVMCOBRA]

[mr0077]

Either circuit will work, but I agree with Ernie, the diagram Fox had is not "typical", As said before, the firewall solenoid was used on Ford starters that did not have a starter solenoid. So if your starter has a solenoid on it, and IF you want to use the firewall-mounted solenoid (not necessary except maybe for looks or safety?), the "typical" way to wire it, described by Ernie and Rick, uses the firewall solenoid to provide battery voltage to the starter motor only when the key is in the start position. This system also needs a wire to trigger the starter-mounted solenoid. I have a jumper wire from the big terminal on my starter solenoid to the blade terminal. Both terminals then become hot when the firewall solenoid is triggered with the ignition switch, so when I turn the key to start, the firewall solenoid energizes, running voltage to the big terminal of the starter solenoid AND the blade terminal of the starter solenoid, causing the starter to spin. You could also run a parallel wire from the key or switched side of the firewall solenoid directly to the blade terminal on the starter solenoid to trigger the starter solenoid.
The diagram Fox has uses the firewall solenoid to trigger the starter solenoid, with the starter motor power uninterrupted, and direct wired from the battery.
Whew! That's difficult to put in words...hope the above makes some sense!

[Excaliber]

Interesting that Fox does have a "rare" Ford starter with the solenoid mounted on it.

As I recall this type of starter was used on certain year Mercury/Lincolns with the big V8's, "back in the day". I haven't seen one of these in years.

[mr0077]

Ernie, I just changed the %&$*@##^% starter on my 1997 5.0L Explorer (actually, pretty easy to do), and it has a solenoid mounted on it also.