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starter motor - testing

Hi friends

Sometimes the starter motor fails. All ground straps and connections have been renewed and cleaned. So the problem - I think - must be found in connection with the starter and/or the ignition switch. Often, the problem disappear, when the engine is warm.

Now...I want to test the starter/starter solenoid in situ. I suppose this can be done by using a 12 V jumper connected directly to the solenoid. Would that work - without any harm?

Regards Palle

Old 01-21-2020, 01:17 PM
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Yes, in fact when I wired up the starter to run the engine on a test stand, all you have to do for starter hookup is run a heavy positive lead from a battery to the large positive terminal on the starter, and then a small positive from a button-switch to the smaller terminal on the solenoid. The ground is taken care of by a heavy cable run from battery negative bolted on to the engine casing. Once you hit the button, the stater cranks as long as the button is depressed.

But yes, in your case, you can hookup a jumper cable to the large positive terminal, then turn the switch on the instrument panel to see what happens. I did replace my starter with a lightweight gear reduction starter from Zims AutoTechnik in Dallas. This starter is light weight and cranks very fast.

Also, for the problem you are debugging, you might take an hour and:

1. pull the battery
2. replace the positive and negative cables, and Lead (Pb) terminals.
3. wire brush the negative (ground) bolt on the left firewall.
4. near a running hose outside, spray the battery posts and top of the battery with spray battery cleaner, and let sit a few minutes, rinse off
5. install new cables and terminals
6. hookup battery

(i bought a brass positive terminal, to which the positive cable bolts in, and melted solder into the end of the twisted copper cable before tightening it down into the terminal)

Rationale for the above maintenance is that as years go by when running a 912, there are a lot of vibrations and the battery can also move(jump). The wear & tear degrades the cables.

Interestingly, last weekend when driving I pulled over and shut off the engine, checked something out, and then tried to restart. Starter just clicked once, and then nothing. It was dusk and getting dark, so I turned on the lights to check battery power, and nothing. Great! So I immediately assumed battery was dead and called for road service to get a jump. After a few minutes of waiting I tested the headlights again, just to be sure, and they came on full brightness, so I left them on opened the front hood and jiggled the battery cables, and sure enough lights turned on/off as I moved the positive cable. So while the lights were on, I tried starting the engine and it cranked right up, so I drove home.

Moral to the story is that unless you pull your battery and make sure cables and terminals are in mint condition, say every 5 years, you could experience what I experienced.

Last edited by wkrtsm; 01-25-2020 at 01:38 PM..
Old 01-22-2020, 09:18 AM
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Thanks a lot for your thorough reply - a great help.

You write "...and then a small positive from a button-switch to the smaller terminal on the solenoid." Is this wire to the solenoid coming directly from the jumper positive or...? Please suggest....

Regards Palle
Old 01-22-2020, 11:18 AM
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No, there's two positive wires going to the solenoid. The first is a small gauge wire that runs from the small post on the solenoid to the ignition switch, and the second is thick heavy copper cable that runs from the large post on the solenoid directly to the positive terminal on your battery.

When you turn the key to crank the starter motor, the small wire carries positive charge from your ignition switch to the small terminal on the starter. The heavy positive cable on the starter is always hot (activated) and is directly wired to the battery (the big red cable).

All the starter needs to crank is a small positive charge to the small terminal on the solenoid, assuming the heavy (thick) positive cable is connected to the large terminal. When the starter's bolted into the transaxle case, you have to maneuver your hand and fingers up into the space where you can feel the two positive terminals on the solenoid. With your fingers up in the slot, you can feel two threaded posts (bolts) on top of the solenoid. One post has large threads like a 8mm thread, and the other is small, like a 3mm or 4mm. When removing the battery I recall the large nut (large post) is a 13mm nut, while the small is either an 8mm, 9mm, or 10 mm nut. (i took my engine out last summer, takes me 15 minutes to disconnect ground wire from transaxle, gas line, engine wires, starter wires, transaxle bolts, engine mount cross bar bolts).

It sounds like you want to override the normal cables hooked up to your starter for testing. So you would have two options:

1. (test if the ignition switch or small gauge wire between the ignition switch and the solenoid is bad). I would do this first. To override the ignition switch (if you think it's faulty) you could just ground another battery (via jumper cable negative to your car body or engine) and then wire up, using small-gauge wire, a button-switch between the positive battery terminal (on the external battery, not the one in your front trunk) and the small positive lead on the solenoid. If this works, your ignition switch is probably bad, since it's doubtful the normal wire between your ignition switch and small positive terminal on the solenoid is bad.

2. (test if the heavy positive cable to the starter is bad). Just hook up a heavy jumper cable (positive) from another battery to the large terminal on the solenoid, then turn the key in the ignition switch to see if the starter cranks. (you have to ground that extra battery on the car or engine). If this works, but didn't work without the jumper cable, then you probably have a bad cable from the battery -- but the problem could be a bad terminal on the battery, or the positive cable could be bad at the battery. If the heavy positive cable failed, then it likely failed at the battery in your front trunk, and not anywhere between or near your starter. Battery acid and/or vibrations (road bumps, engine vibration) can be causal for degrading a good cable (positive or negative) to the battery. You could also have a bad terminal that the cable connects with. Or, there is too much acid corrosion underneath the terminal, or the battery is bad.

Hope this helps.

Last edited by wkrtsm; 01-22-2020 at 09:12 PM..
Old 01-22-2020, 08:40 PM
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I am sure it will help me - thanks a lot. And you are right about overriding the normal cables.
Reg Palle
Old 01-23-2020, 08:38 AM
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Did you get the issue solved?
Old 01-26-2020, 07:03 PM
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Thank you for following up
Well...I have tested/measured the wire connections from ignition switch to starter.
It seems that the ignition switch is the problem. To day I will try to test the system by using a engine starter button - and if this works installing this button. I will come back
Reg Palle
Old 02-10-2020, 04:17 AM
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Hi again

Problem solved
I succesfully installed a starter engine button (attached photo) with red light when starting. Now my 912 starts every time - and much more powerful. Thanks for your assistance.

Reg Palle
Old 02-14-2020, 05:22 AM
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Glad that you were able to solve the problem. At least you now know the wiring configuration for the starter solenoid. However, what do you tell someone when they ask: why didn't you just replace the ignition switch?
Old 02-19-2020, 01:02 PM
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Well, a new correct switch is too expensive - price, postage etc.
(The ignition as such is still via the original switch)

This actual solution with a button is cheap, simple, smart and does it perfectly. So I am glad, too. Now I really look forward to start my outlaw P912 - every time

Old 02-20-2020, 09:42 AM
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