LX176 key voltage to solenoid is low

[deckeda]

The starter solenoid isn't engaging. Battery connections are clean, new and tight. The battery's at 12.6 volts currently. Same measurement at statrter post and at the wire coming off the battery that feeds the key switch. Dash lights work etc, carb relay works, main relay I can hear click also. PTO can engage etc.

With key OFF my meter registers "0.01" volt at the wire that goes to the relay that then goes to the starter solenoid.

With key to "run" my meter shows about 1/4 volt.

With key to "start" my meter shows around 1.5 volts at that wire.

Am I being dumb, or shouldn't that wire be at ZERO volts unless the key's at start, at which case it should have 12v?

 

[bertsmobile1]

Nearly all of the switching on mowers is done on the ground side of the circuits
So check for ground / no ground situations.

Better still, let us know why you are doing voltage readings.

 

[mechanic mark]

https://www.google.com/search?q=wir...KHcUnAAoQ9QEwAHoECAgQBA#imgrc=0P_bxnYomgrmGM:

 

[deckeda]

So to engage the starter solenoid the small wire on it gets grounded, not 12+v sent to it from the key. All these years I've had it backwards. I didn't really see it that way on the diagram but I'll look again.


I suspect the starter will run tomorrow, after I sit in the seat and press the brake (been a long day and I've been working with another machine that doesn't require that, sorry).

 

[bertsmobile1]

Circuit diagram
View attachment LX 172-188.pdf

Testing proceedure
View attachment LX 172-188-1.pdf

Lots of places for a bad connection to rob the purple /white wire of power

 

[deckeda]

Thanks for that Bert.


Note it uses 12V to trigger the relays that switch ground.

Yes, and mine has a Bosch-type relay prior to the solenoid (mounted right near it) I do not see in the factory diagrams. It gets constant 12+ from the starter post, with the purple/white trigger wire being what's looped through it over to the solenoid's small tab.

 

[deckeda]

This part at the bottom of the page,

"11. Starter solenoid (look for) Battery voltage.
(if not normal) Check purple/white wire No. 721 and connections."

So I was correct earlier? Purple/white wire does send 12 (POS) to solenoid when key switch = start position.


Thought I'd read here somewhere that Deere added, or had dealers add, the 2nd relay to help ensure the solenoid got power. Must have not updated the diagrams.

 

[bertsmobile1]

If you have a relay on the purple wire before it goes to the solenoid, that relay will usually be switched by a safety circuit
All safety circuits are ground circuits

If the purple wire is wired in parallel with the relay, then I have no idea what it does.

There are a lot more circuit diagrams for an LX176, but they are serial number dependent.
When you said the relay I had assumed it was a starting relay without checking the actual wiring diagram which is very naughty of me.
Pull the relay and check weather the purple is a trigger wire or the switched wire
The relay diagram is on the top of the relays and the pin numbers are on the bottom.
From memory there is a row of 5 relays between the engine & the mower so you can swap them around to see if the relay is working properly.
I have a stack of short patch wires I use to bypass the relays when I am testing them.