Here is a detailed explanation of the reason a Series Wound starter motor still rotates the same way regardless of battery polarity.

When Battery Polarity is reversed both Field and Armature currents are reversed [Because it is Series wound]-rotation direction remains the same.

If the Starter were to be dismantled and either the field or the armature connections reversed the Starter rotation would reverse

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Check that dynamo and control box are connected correctly. The larger dynamo terminal must be connected to control box terminal ‘D’. The smaller dynamo terminal connects to control box terminal ‘F’. Check the earth connection to the control box, terminal ‘E’. Check that the brown wire between the starter motor and the dashboard ammeter is intact. Check that the brown/yellow wire between the ameter and the regulator box is intact. Also that the dashboard ammeter shows a discharge when a 12 volt light bulb is lit using the brown/yellow wire which goes to the regulator box.

See this page for MF35 wiring diagram.

Switch off all lights and electricl accesories, disconnect the terminals from the dynamo. Start the engine and run on tick-over. Connect a volt meter from terminal ‘D’ to terminal ‘F’ (on the dynamo) and speed up the engine revs. The volt meter should read between 2 and 4 volts. If you get a zero reading then check that the brushes are free. If you still get a zero reading then it is the armature that is at fault.

Leave volt meter as above. Then also connect an amp meter from terminal ‘D’ to terminal ‘F’, increase the engine speed slowly and the voltage should rise with increased speed. Adjust the volt meter (by using the engine revs) to read exactly 12 volts, then the ameter should read 20A. If the volt meter reads 2 to 4 volts then this indicates a broken field (electric magnet is not working correctly). If you get 12 volts, but only 4 amps then this indicates an earth field (short circuit).

Excessive sparking at the commutator in the above test indicates a defective armature which should be replaced.

If you pass all of these tests for the dynamo then it may be the regulator box which is at fault. The regulator box is quite cheap to buy if this is the problem.

Per Said:-

I’ve had an inquiry about converting from a Lucas dynamo to a Delco 10-SI alternator. This fellow has an FE35 which is earlier than 1959, and it presently uses positive ground. I believe older models came with positive ground whereas my own ‘59 has negative ground. I don’t know if that is original or if it has been changed later.
His question is: since the new alternator needs negative ground, how do you convert the starter motor to negative ground? In order to maintain the correct direction of rotation (clockwise as seen from the transmission) do you simply reverse the plus and minus wires on the starter? I.e., do you now attach the positive battery wire to the top terminal on the solenoid and the (now negative) ground wire to the post on the end of the starter casing?
Thanks for any thoughts you or Ian may have on this.
Per

Then before we had chance to reply, Per e-mailed us again:-

Hi Steve,

I think the problem about converting an FE35 starter motor from pos to neg ground has been solved. Here’s what an auto-electric expert wrote:
“The starter motor doesn’t care about polarity so you don’t have to change those cables. Same with switches, lights, solenoids and the like. Most ammeters will indicate backwards unless you swap the wires from one post to the other and vice versa. Swap the cables on the battery, wire the alternator like your schema shows, turn on the lights to check the ammeter shows discharge and that should be all.”
–Per

We then gave Per a few more things to consider…..

Hi Per,

It is the same starter motor on the MF135 (-ve earth) as on the MF35 (+ve earth), so I would think that it is just a case of swapping the battery leads over as you suggested.

The gentleman will need to make sure that the voltage regulator box is
disconnected and the wires made safe.

Also will need to swap the ammeter wires over.

Also consider the max output in Amps of the altenator and the corresponding size of the wire to carry this current.

Also consider the maximum capacity (Amps) of the ammeter when choosing the altenator output current.

Hope this helps.

Regards,

Steve and Ian.

If you are finding it difficult to follow the wiring diagrams, then the process is shown in detail on the MF35 Engine Rebuild DVD.   Click the link and watch the trailer to the DVD.

Just click the link - mf35-wiring-diagram001 - . The .pdf file is in high resolution in order to view the small print.

Or another good wiring diagram can be seen on Per’s Soggers site which is all about his FE35. Per’s is on a negative earth with twin batteries.

Comments….
1
john nelson says:

December 6th, 2008 at 10:00 pm
My TO35 won’t turn over w/starter button. I replaced solenoid but won’t activate starter. I can start tractor jumping from solenoid to starter cable and remove starter cable after starting to stop starter motor??? I am electrical ignorant….HELP

2
Vintage Tractor Engineer. says:

December 10th, 2008 at 6:07 pm
Hi John,

I would say that it could be one of a few things that could be causing the
problem.

Try the safety isolator switch (just in front of steering box). Make sure the tractor is out of gear (R,1,2,3), join the wires together on this switch (white/blue wire to the white/red). If it then startes with the ignition switch then that is the problem

Next try the ignition switch to see if it is faulty.

Next thing sould be the whole wiring loom (or part of it).

Have a look at this page and the wiring diagram.

Hope that helps.

Steve, VTE

When fitting screw clamp type battery terminals to the leads it is important to get a good contact between the terminal and the lead. The problem is that when the clamp screws are tightened, the wires tend to spread out which results in a poor electrical connection and hence an inefficient transfer of power when under starting load.

An improved connection can be achieved by running solder into the wires before the terminal is fitted, as shown in the photo below. This will make the end of the cables rigid, allowing the clamp screws to take a firm hold. If this has not been done, then the connection is more likely to deteriorate and could be the cause of poor starting performance.

Care is needed during the soldering to make sure that the insulation is not damaged. The correct flux should also be used. Beware, due to the conductivity of copper, the heat will travel quickly and a long way along the cable.

When the new cables and terminals are fitted, anti-corrosion gel should be applied to the exposed metalic surfaces around the battery terminals to prevent corrosion.

Remember, many battery terminal clamps need a spanner size of 5/16ths Whitworth. This is indicated when both 1/2in AF and 13mm spanners are too small, whereas 9/16in AF and 14mm spanners are too large. There is no need to overtighten the clamp bolt if all the surfaces have been cleaned before connecting. Do not clean the battery posts using a wire brush as this can cause sparks and thus an explosion of the hydrogen gas in the battery.

Other areas to check on the leads are the insulation on both leads and the integrity of the terminals on the starter motor and earthing point.