Sticking starter solenoid - I think.

[lw395]

All, TE, I so appreciate your help sofar.
Heading down to the boat today to investigate.
Armed with fully charges spare, and lengths of wire and crocclips.
And I have spent some time this week going through the 'Tony Brooks' website, as recommended reading in this and other threads.

Brief recap.
Engine Battery is healthy. Engine normally starts easily and predictably. Key turn produces NO CLICK or NOISE AT ALL, and the engine panel lights and temp gauge go out and drop to zero........

What is this telling us?
Turning the key causes the panel lights to go out.
This means the volts at the panel lights are seriously reduced when the key is turned.

This means there is either a fault in the battery-panel-battery circuit (high resistance, bad connection, dead battery), or the solenoid is pulling so much current that the good battery delivers too few volts to light the bulbs.
The solenoid is not clicking, the starter is not turning.

Put the meter across the battery, Should be around 12.7Volts.
Turn the key. What does it drop to?
Either it's going to be not much of a drop, implies a circuit fault
Or a big drop. Implies either poor battery OR very big current being drawn. If you can't measure the current, see if anything is warming.

Since the solenoid is said to be not 'clicking', the power won't be going into the motor itself, it must be heating the solenoid or some wiring.
Find 12V and GND at the panel. One side of the oil light will normally do for 12V.
Turn the key again, what do the volts drop to here? If the drop here is much greater than the battery drop, there is resistance between battery and panel. You can either look for that with the meter, or strip/clean/reassemble methodically until it's sorted.

The solenoid (working OK) draws a fair old current. 10 or 20 amps? The battery should supply this for hours without dropping below 12V.

 

[VicS]

What is this telling us?
Turning the key causes the panel lights to go out.
This means the volts at the panel lights are seriously reduced when the key is turned.

This means there is either a fault in the battery-panel-battery circuit (high resistance, bad connection, dead battery), or the solenoid is pulling so much current that the good battery delivers too few volts to light the bulbs.
The solenoid is not clicking, the starter is not turning.

The lack of any sound when the key is turned to the start position, despite the lights going out, puzzles me if any of the theories about solenoids, starter motors , brushes or even bad connections are correct.

If the solenoid is pulling in and putting a big load on the circuit through a non turning starter motor I'd expect to hear a distinct "clonk"

A possibility, which could explain this is a is a defective key switch!

 

[lw395]

The lack of any sound when the key is turned to the start position, despite the lights going out, puzzles me if any of the theories about solenoids, starter motors , brushes or even bad connections are correct.

If the solenoid is pulling in and putting a big load on the circuit through a non turning starter motor I'd expect to hear a distinct "clonk"

A possibility, which could explain this is a is a defective key switch!

That would explain a lot!
Again, watching the battery volts would help narrow this down.
Life is easier with motorbikes, I just put the headlight on and if it doesn't dim a little bit, nothing is drawing much from the battery. If it goes really dim, something is drawing more than the battery wants to part with.