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Starter Solenoid Voltage Leak....maybe?

electrical engine

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#1 KiwiMini77


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Posted 01 July 2021 - 12:10 PM

Hi people


I don't have any actual issue starting my wee car, but I did notice something I find odd and I cannot find reference to it being normal, so I wanted to see what a) others thought and b) whether anyone else had ever seen it (or tried what I tried).


Fitting a new gauge to the car, I was poking around the engine bay, looking for switched power.  I did eventually wire it to one of the fused options and this whole but is largely irrelevant except that it explains why I was under the bonnet with a multi-meter.


Anyway, a mate asked me about the rather wire-covered box bolted to the frame.  I explained that it was the starter relay and for fun, I used the multimeter to show him where the power and starter lead were.  I had my black lead grounded and was probing using the red lead, so all I was doing was earthing out anything I touched. 


Now, the meter showed the requisite 12.4 volts on the power lead from the rear of the car and zero when I touched the opposite main pole.  However, it registered somewhere between one and three volts when I touched both the upper and lower signal wire (ie: the spade connectors that stick out to either side).  I thought this was a bit odd - the ignition was off and there should be no power as far as I know at either terminal unless someone has the key in the "Start" position and the car is cranking over........or am I wrong?

To me, it seemed weird that power was on either of those connections at all.  I did not pull the wires off and check the terminals again to double check (silly me) whether it was wire or solenoid that had the possible 'leak', but instead I jumped on here to see whether there SHOULD be power there.


- If there is power at the solenoid spade connections without the wires connected, is the solenoid stuffed?

- If there is power at one (or both) of the wires that connect to the solenoid even when the ignition is switched off, is this normal?

- Why would there be power in those wires?


As I said, the vehicle starts, runs and drives as normal  The battery does not deteriorate over a week between starting and the starter will still turn the engine over at its normal quick rate.  I don't actually HAVE a problem as yet, but want to know if I should do something about something weird that is happening BEFORE it turns into a problem.


Any ideas? 

#2 GraemeC


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Posted 01 July 2021 - 12:35 PM

It could be that the earthing of the solenoid is not perfect - it only earths through its bolted fixing to the inner wing which is a) painted and b) prone to corrosion.  So a lightly higher resistance here can see the system trying to earth back through an alternative path - in this case those cables.

#3 Ethel


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Posted 01 July 2021 - 01:25 PM

The spades that aren't on the screw terminal for the battery?


One is the supply for the ignition that bypasses the ballast resistance, if you have ballasted ignition (yellow/white wire attached to it)


The other operates the solenoid, so you'd be measuring the voltage drop across the solenoid's windings - but it shouldn't be live unless you're actually cranking the starter.


If you had the ignition on, you'd have picked up voltage coming through the ballast wire that could have been split partly with the coil's primary winding, if the engine stopped with the points closed. You'd have the other share which your meter would be grounding via the resistance of the solenoid windings.

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