Starter problems?

I took the starter out of my 92' F-150 and hooked a pair of "jumper cables" directly to the starter from the battery. I then used a screwdriver to jump the terminals to activate the starter.
The starter worked.
I reinstalled the starter on the truck. Then I used the exact same procedure. I hooked the jumper cables to the starter, while it was on the truck, directly to the starter. The starter would not work. The starter would not engage.
I did this about 8 times.
Finally, I took the solenoid ,that is attached to the starter, apart and worked the plunger that goes from the solenoid to the starter motor itself.
Then I used the jumper cables again direclty to the starter and the starter worked much better.
I reinstalled the starter on the truck and I used the jumper cables directly to the starer. For the first time the starter made a clunking sound.
It still would not kick the engine over.
What is the problem?

Hi, I'm not familiar with the F-150, but I'm an electronics engineer so I'd be hopeful of being able to help you with this. On the starter motor solenoid, you will have three terminals - two large, one small. Can we refer to those as the B, M and S terminals, and then we'll know that we're talking about the same thing. I identify those terminals like so:

B terminal (large) has heavy gauge cable coming in either directly from battery positive terminal, or from output side of firewall solenoid (if fitted).

M terminal (large) has short length of heavy gauge cable which carries current from solenoid into starter motor winding, when solenoid has been energised.

S terminal (smaller than the other two) has much smaller gauge wire, which carries current to energise the solenoid when ignition is switched to 'Start' position.

Ok, so could you clarify a few points, please.

1. When you tested the starter on the bench, did you bridge the B terminal (large) to the M terminal (large), or the B terminal to the smaller S terminal?

2. When you reinstalled the starter on the truck, and hooked up the jumper cables, were you still using a screwdriver to bridge terminals (and if so, then which two - B to M, or B to S?), or were you cranking via the ignition switch?

3. As I said, I'm not familiar with the F-150, so could you tell me if that has a firewall solenoid, in addition to the solenoid which sits atop the starter motor body.

Oh yes, and do you have access to a multimeter, if needed. Thanks.

I just typed in a 30 minute response and then I was told I must be logged in to do that, which I was logged in.

Selectron, thank you for you response, from D.J.

I wanted to eliminate any wiring problems. So, I stood the starter on the negative battery post. I connected the positive wire, which I had just taken off of the truck, from the battery to the starter, I got very little spark, I took the starter to Autozone, which had recently said the starter was good, I took the starter apart and cleaned the brushes.

Autozone tested the starter, nothing happened, the starter now test to be bad. I took the starter home and took it apart. I cleaned the brushes.
I hooked the starter to the fender ground which is about 8 inches from the battery. I hooked the positive wire of the starter to the positive side of the battery, with the original starter cable. I jumped the terminal with a screwdriver and it was like I was welding. There was much more current than before.

Sorry you lost your original reply - I've read about that happening before. I usually type in Notepad and then copy and paste from there, so if the forum loses the post I can just paste it in again.

Anyway, back to your starter. What I was trying to find out with my list of questions was whether the problem is in the starter motor itself, or in the solenoid (specifically, the solenoid plunger electrical contacts), or in the circuit which feeds the solenoid via the ignition switch and transmission safety switch (and possibly a firewall solenoid).

If you're comfortable about dismantling the solenoid, and working on the starter brushes then chances are that you understand well enough how it all works, but I'll run through it briefly.

As you know, there's a heavy cable running from battery positive to the large B terminal, and there's a short length of equally heavy cable running from the M terminal into the starter motor windings. In order for the motor to operate, current must pass from the B terminal to the M terminal - that task is performed by the solenoid.

The solenoid (which is energised when 12V is applied to the smaller S terminal) performs two functions - the first is to move the starter pinion forward and into engagement with the engine flywheel - that's a purely mechanical function. Then as the pinion comes into engagement with the flywheel, the solenoid performs its second function - this time an electrical function, as the plunger bridges two terminals - the B and M terminals - and passes current to the starter motor, which then operates.

Ok, so when you are testing the starter on the bench, I'm still not clear which two terminals you are bridging. If you bridge the two large terminals then the motor will run, but you will be bypassing the solenoid, so that tells you nothing about the state of the solenoid electrical contacts. Therefore, it's better to bridge the B terminal to the smaller S terminal - this causes the current to flow from B terminal to M terminal via the solenoid's internal electrical contacts, so it's a more meaningful test.

I know you've cleaned the motor brushes and I know that you've checked the solenoid plunger mechanical action, but did you take a look at the solenoid's internal electrical contact which bridges the B terminal to M terminal? When the engine is cranking, that will be carrying a couple of hundred amps, so it has to be in good condition and making a solid, reliable contact with the two terminals.

If the starter is still removed from the vehicle and if you're not sure about the condition of the solenoid's electrical contacts, then you might want to open it again and take a look at them.

I can suggest some things which you might try, if the starter still fails to crank, but I'd need to know if you have a firewall solenoid in addition to the solenoid attached to the starter body.

The solenoid on the starter is enclosed. It cannot be opened. The only part that is accessible is the plunger, which is in good working condition.

Yesterday, I reinstalled the starter on the truck. I used a screwdriver to jump the terminals on the starter. The terminals I jumped are; by your terms, terminal "B" to terminal "S". The engine cranked over and started. The truck will not start using the key. There is a relay on the fender. I tried starting the truck using the screwdriver and I got very little spark.

Ok, now we're making progress. If the engine cranked and started when you bridged the B terminal to S terminal, then the problem is not in your starter or solenoid - you may well have had a problem there, but if you did then the brush cleaning and whatever you did to the plunger appears to have fixed it, so you can now forget about those.

Your problem is in the circuit which feeds 12V to the small S terminal on the solenoid - either that terminal is not receiving voltage, or it is receiving a reduced voltage, because of a fault further back in the circuit.

If you want to prove that to yourself, then get a length of wire of the same gauge, or heavier, as the wire which connects to the small terminal on the solenoid, and connect one end to that terminal (the S terminal). Then route the other end up to near the battery - strip a quarter inch of insulation from the end and then tie it to something. Note that you're not connecting that end to anything - just have it sitting there ready. Then put the transmission into Park or Neutral (for an automatic) or Neutral (for a manual), apply the parking brake and switch the ignition to the 'Run' position. Then go to the battery and touch the bare end of that wire to the battery positive terminal - your engine will crank and fire - as soon as it does, remove the wire from the battery terminal and tuck it safely out of the way.

I'll make some suggestions for finding the fault but I'll put them in a separate post, to make it easier to follow.

I just went to pep boys and purchased a Negative battery cable. I hooked it to the Negative battery post and to the starter. When I jumped the terminals I got very little spark, again the truck will not start.

The small S terminal on the solenoid will be fed thus:

fuse - to ignition switch 'Start' contacts - to transmission safety switch - to firewall relay coil terminal - then from firewall relay output terminal - to starter solenoid S terminal.

Somewhere along that path you have a problem which is causing the voltage to drop, so the full 12V is not arriving at the solenoid S terminal. That might be a problem with the ignition switch 'Start' contacts, or a bad wire anywhere along that path, or a loose, dirty or corroded connector. I doubt that it's the firewall relay because even when you bridged it with a screwdriver, the engine still didn't crank.

You didn't say if you have a multimeter - if you do then start tracing the voltage back from the S terminal until you find the point at which it drops.

If you don't have a meter then you can quickly determine if the fault lies before, or after, the firewall relay by using a jumper lead. With the transmission in Park or Neutral, and with the ignition switched off, bridge the battery positive terminal over to the firewall relay coil terminal, just momentarily, and the engine should crank. If it does crank then your fault is before the relay coil terminal. If it doesn't crank, then your fault is between the relay output terminal and the starter solenoid S terminal.

And this is how to identify the terminals at the firewall relay:

Relay input terminal will have a wire connected directly from the battery positive terminal.
Relay output terminal will have a wire running from there to the starter solenoid S terminal.
Relay coil terminal is, by elimination, the third terminal - the connection for that will come out of the wiring harness and this terminal will probably be smaller than the input and output terminals.

If the fault is after the relay output terminal then that's easy to fix because it should just be a single wire from there to solenoid S terminal - just replace it.

If the fault is before the relay coil terminal then you'll probably need a multimeter to locate it. I'd disconnect the battery negative terminal, set the meter to the resistance range and then just do simple resistance checks along the feed path to locate the fault - it will be a high resistance or an open-circuit.

Good luck, and let me know if you don't follow any of that.

Oh and if you need a wiring diagram, then go to this thread:

http://www.automotiveforums.com/vbulletin/showthread.php?t=890909

... follow the instructions in the first post and then select your year and model. Then if it doesn't say 'Wiring Diagrams' on the first menu that appears, click instead on Repair Procedures, then Chassis Electrical, and you should find the wiring diagrams in there.

I just went to pep boys and purchased a Negative battery cable. I hooked it to the Negative battery post and to the starter. When I jumped the terminals I got very little spark, again the truck will not start.
I don't really follow that, because there has never been any reason to suspect a problem with the negative side of the circuit. Are you saying the starter is still fitted to the vehicle but when you bridge the B terminal to S terminal, it no longer cranks?

yesterday, that was the big break, when I hooked a good ground to the starter. That was when I got the most action out of the starter. I got the truck to start.

I just used a speaker wire going directly to the S- terminal. I touched it to the Positive side of the battery and the engine almost turned over. Now it will not do anything. I am still getting a spark at the battery terminal when I touch the wire.

I have 2 problems, 1, the starter is not working. It worked one time yesterday, 2, the starter does not work with the key. Before I can trace out the circuit, I need to get the starter working every time.
That is the purpose of the Negative battery cable. When the starter has good negative and positive power, and the S terminal wire is good and the starter still does not work, I know something is wrong with the starter.

I'm wondering if your battery is running flat. You didn't say if you have a multimeter, but if you do then you should read around 12.6V across the battery terminals. If you don't have a meter then I'd just put it on charge anyway and then see if the symptoms change when it's freshly-charged.

I do not have a multimeter. I wish I did. The pattern is that the starter works and then it does'nt. Something is wrong with the starter. It is not a low battery, it is not the wiring, I have the starter wired directly to the battery and it does not work.

Selectron, you have been a great help, I appreciate it. If I may ask for further assisstance,
I have the starter off of the truck.
The starter and battery is sitting in my living room.
I am using jumper wires to activate the starter.
It is working every time.
If I reinstall the starter on the truck it will not work.
That is what has been happening.

Correct me if I am wrong.
There are 2 components of the starter, the plunger which engages to the flywheel, and the

Hmmm, your post is incomplete - are you using the 'Quick Reply' box? If so then try clicking on the 'Post Reply' button instead, near the bottom of the page on the left - I've always found that to be reliable. It also gives you a bigger window to type in. Better to type in Notepad though, and copy and paste, then you can't lose it.

So I don't know what else you were going to say, but I'll reply to what you have said.

First thing to be aware of is that when you're testing a starter on the bench, it doesn't really simulate the starter's normal working conditions, because it is running with no load. So just because it appears to spin freely and reliably on the bench, that doesn't mean it will still perform that way when it's back in the vehicle, where it will be expected to work against the considerable load of cranking the engine and overcoming the compression in the cylinders. The other thing to be aware of is that the current will be greatly reduced when it's running on the bench. When it's cranking the vehicle it probably draws a couple of hundred amps or more, but when it's working against no load, on the bench, it might draw as little as - just a guess - but maybe as little as fifty amps.

When bench-testing, be sure to simulate the same wiring conditions that you have on the vehicle - so that's the negative battery terminal to the starter casing, positive battery terminal to the solenoid B terminal, and then bridge from B terminal to S terminal to power the motor via the solenoid. Don't just bridge directly from B terminal to M terminal, because that will bypass the solenoid, and therefore doesn't simulate the starter's normal wiring circuit.

When you reinstall the starter on the vehicle, the only way to rule out wiring problems would be to use three jumper leads. Two will be required to carry a massive current, so they would need to be heavy gauge, like regular jump-start leads, and then the third lead would only be to energise the solenoid, so that can be much thinner - use the gauge of the existing S terminal lead as guide.

You would connect the leads as follows:

Negative lead (heavy gauge) from the starter motor body (or engine block if that's easier) to the battery negative terminal. Note that I said the terminal - it isn't good enough to just clip the jumper lead onto the battery connector, because that might have a poor connection to the battery, so hook right onto the actual negative terminal itself.

Positive lead (heavy gauge) from the solenoid B terminal to the battery positive terminal - and again, that means right onto the terminal - not just clipped on top of the positive terminal connector.

S terminal jumper lead - only a small diameter lead required for this, because it only carries a low current, to activate the solenoid.

Then ensure that you are in Park or Neutral, and with the ignition switched off, apply 12V to the S terminal lead - it doesn't matter whether you get that directly from the battery or just take it off of the B terminal. On second thoughts, the battery would be better, because you don't want to risk knocking the jumper lead off of the B terminal and causing a short-circuit. Because the ignition is switched off, the engine won't fire - this is purely to test the starter motor's cranking ability.

If you can arrange that, and do it safely, then that bypasses all existing wiring and would be the best indicator you're going to get, as to whether the problem is in the starter, or in the vehicle wiring.