Starter motor query

[sogood]

A short and simple question. Should the small stud that takes the red/yellow wire on the starter motor go to earth? I suspect not, but mine does on my new replacement starter. I believe the red/yellow is the feed from the ignition to engage the solenoid. Thanks in advance.

 

[rotrax]

A short and simple question. Should the small stud that takes the red/yellow wire on the starter motor go to earth? I suspect not, but mine does on my new replacement starter. I believe the red/yellow is the feed from the ignition to engage the solenoid. Thanks in advance.

Only fairly rare Earth Return starters will have a dedicated earth wire, and that will be a sodding great big one.

Normal starter will have the heavy wire to a large stud, perhaps 10mm, and a spade terminal for the solenoid activator, affixed to a perhaps 5mm stud.

 

[sogood]

Yes thanks. Mine has the big heavy black earth and everything else is as it should be. This is a brand new starter and I suspect it may be faulty. When I try to start it on the key it just "rattles" the solenoid, like you might get with a low battery. But my battery is also brand new and fully charged.

 

[Billjratt]

Sounds like you have a duff connection on either of the heavy leads, Check the ground, and any shunts in the circuit. Metwer from the battery studs to see lost volts

 

[sogood]

Thanks. I only mention the wire colour for identification purposes, as the yellow /red seems to be the standard from the ignition to the starter, at least on the Volvo diesel engine that I have. It goes onto a small stud on the starter, and is the only place that it can go to. On my old starter this stud is not earthed, if that helps.

 

[sogood]

Just to clarify, the stud gives continuity to ground, even with the yellow/red wire disconnected, so any potential short is not in the wiring.

 

[PaulRainbow]

Just to clarify, the stud gives continuity to ground, even with the yellow/red wire disconnected, so any potential short is not in the wiring.

If you are checking that with a multimeter, you will get continuity, because you are measuring across the solenoid coil.

You can rule out the red/yellow wire, the key switch/starter button, or anything else in between by sorting the big red cable terminal to the small solenoid terminal. It should start, if it does not it will be a bad connection on the main cables or a faulty starter.

 

[sogood]

Can you clarify which "big red cable" you refer to? There are several. And I imagine you mean "short it". The motor does function properly when I short it, as per a bench test. My question is, should the small stud that takes the red/yellow wire go to ground/earth. And if not wouldn't that mean that the starter is faulty?

 

[VicS]

Just to clarify, the stud gives continuity to ground, even with the yellow/red wire disconnected, so any potential short is not in the wiring.

You will find a very low resistance . A solenoid draws quite a large current, initially at least . The one I have checked, on a Volvo car, draws approx 40 amps and the resistance the earth / ground /negative, or what ever you prefer to call it, is only about 0.3 ohm.

Solenoids usually have two windings a "pull in winding" that draws a high current and a "hold in" winding that draws a lower current ( I have not measured this but I believe about 8 to 10 amps ) The 40 amps I measured would have been the total current through both windings.
The "pull in "winding is by-passed when the main contacts close.
(None of this is apparent from the outside)

If there was no continuity between the small stud and earth/ground/negative on your old starter it must have been faulty. There has to be continuity for current to flow !

If your new starter has a separate heavy negative connection but the old one did not, gromd this connection to the engine block, preferably to the same place as the battery negative connection otherwise to one of the motor mounting bolts.

 

[PaulRainbow]

Can you clarify which "big red cable" you refer to? There are several. And I imagine you mean "short it". The motor does function properly when I short it, as per a bench test. My question is, should the small stud that takes the red/yellow wire go to ground/earth. And if not wouldn't that mean that the starter is faulty?

Only one big red cable going to the starter solenoid, from the battery. short that to the small terminal. The small wire is not connected to ground, it is positive when the key is turned to the start position.

 

[sogood]

I'm confused. The two previous post seem to say opposite things. FWIW, the new starter is exactly the same as the old one, same wires, same connections, including the heavy ground to the block. Vic says "there has to be continuity between the small stud and ground". Paul says " the small wire is not connected to ground" Can someone clarify please?

 

[alan_d]

I'm confused. The two previous post seem to say opposite things. FWIW, the new starter is exactly the same as the old one, same wires, same connections, including the heavy ground to the block. Vic says "there has to be continuity between the small stud and ground". Paul says " the small wire is not connected to ground" Can someone clarify please?

Yes, they are both correct. The small stud is not connected directly to what we are calling ground, but is connected to it via the windings of the solenoid which are very low resistance. Thus there is electrical continuity between the stud and ground (otherwise no current would flow and the solenoid would not work) but it is not connected directly to it i.e. there is not a short circuit.
Think about a light bulb. If you connect together the two wires leading to the filament it will not light up and you will probably blow the fuse. If, however, there is no continuity between the wires (via the filament) the light will not illuminate , i.e. the bulb has blown.

 

[VicS]

I'm confused. The two previous post seem to say opposite things. FWIW, the new starter is exactly the same as the old one, same wires, same connections, including the heavy ground to the block. Vic says "there has to be continuity between the small stud and ground". Paul says " the small wire is not connected to ground" Can someone clarify please?

If you disconnect the red/yellow wire from the solenoid you will find no connection between it ( the wire) and earth.
If you turn the key to the start position ( or switch on and press the start button if you have a keyless panel) you should find 12 volts on the wire.

If you reconnect the wire then turn the key/ press the start button current will flow from the battery ( probably via a relay, through the wire , through the solenoid coils and back to ground and battery negative . If there is no continuity to ground current will not flow and the solenoid will not operate.

Edit Overtaken by Alan D

 

[sogood]

Thanks to both of the above. All cleared up now.