TM1820 Starter circuit

[pycoed]

Yanmar YM 1820 - does not start via ignition key. Previous owner had disabled connection to the starter solenoid & added jumper wires from solenoid battery & start terminals, now I think I know why.
He had also, wisely in my opinion, added a 25 amp blade fuse link in the white/red ignition switch feed from the starter solenoid. I have now proven all circuits on the tractor. Everything works except the starter connection from the ignition switch. I have proved the cable from the ignition switch via the clutch switch, which works fine, to the vacant wire next to the starter solenoid i.e the original one.
Battery connections are clean & have dielectric grease, ditto earth to chassis removed cleaned greased, replaced - neither looked corroded at all. I've done the same on the solenoid too.
Every single time, with the original tractor wiring connected, when you turn the ignition key to start, this fuse will blow. If I connect a jumper cable from the battery connection on the solenoid to the start connection the engine starts instantly and the 25 amp fuse stays intact. For some reason, which at the moment escapes me, it seems as if with the original wiring the starter tries to draw its start current via the ignition switch rather than the battery cable. At present I am stumped as to why.
I've come back to the house for a coffee & I'm taking the dogs out for a run & clear the brambles away from the transit box that is pencilled to sit behind the Yanmar, then I'm going to try an additional earth strap from a starter mounting bolt to the chassis. I'm half minded to try inserting a starter relay in circuit, but I wanted a simple little tractor & I've already got a thermostart timer I didn't want!!
Opinions gratefully received!

 

[ponytug]

Is there a reason to think that this particular starter solenoid would draw less than 25A? i.e. Have you measured the draw? A a rule, at least in my experience, starter solenoids aren't particularly frugal devices.

All the best,

Peter

 

[pycoed]

None at all, except that 25amp was the fuse I found in it. Looking at the conductor size, I'd be surprised if more than 10 amps though.
I've no direct way of measuring the current (multimeter max of 10amp), I'll check the ohms & work back from there, but I wonder if just a slow-blow fuse would do it.
I did try with a 30amp, but that blew too. I don't know what ordinary automotive blade fuses are rated, I'd guess not slow-blow

 

[ponytug]

Any guesstimate on the wire gauge? Have a neighbor with a clamp on multimeter that you could borrow?

From memory my solenoid connection on my current, non-Yanmar, tractor is either 10 or 12ga, but then again the wire only has current on it for a few seconds.

All the best,

Peter

 

[alexpops]

Are you sure you don't have a short in the original wire between the key switch and the solenoid start?

 

[pycoed]

I get 12v at the original solenoid wire when clutch depressed & key to start. 0v when clutch up. I've checked continuity from ignision switch to clutch switch & from clutch switch on to solenoid. All seem OK.
It starts easily by jumping 12v to the solenoid start with no indication that the temporary wire heating. I even ran the starter for 10 seconds by keeping the stop cable pulled & temp wire didn't warm at all. Yet there IS a problem somewhere?????

 

[alexpops]

Bad Key Switch?

 

[garry1p]

Strange for sure, turn the key +12V energize the solenoid through the clutch (switch) once energized solenoid contacts made 12VDC to the starter!!
What could possibly go wrong? For some reason it is never that simple.

You said you verified the wiring through the clutch switch to the solenoid and you jump around the solenoid and it starts OK so my guess is the solenoid itself or the key switch.

On edit I guess I was typing this as you were posting

I agree key switch.

 

[pycoed]

Any guesstimate on the wire gauge? Have a neighbor with a clamp on multimeter that you could borrow?

From memory my solenoid connection on my current, non-Yanmar, tractor is either 10 or 12ga, but then again the wire only has current on it for a few seconds.

All the best,

Peter

My fully equipped neighbour departed yesterday to Germany for a fortnight to visit relations. I'm opening & closing their chickens for the duration!
Our wire guages are different from the AWG but even keeping the stop cable pulled & running the starter on the small guage temporary cables for 10 seconds or so results in no discernible heat build up at all in the wire, yet the tractor wiring immediately blows even a 30A fuse. This is so simple... yet just not working. AAArgh.
I'll try putting various 55W bulbs at the end of the start wire to see what happens & I think I have some MAXI slow blow fuses somewhere to try as well.

 

[alexpops]

https://www.amazon.com/MGI-SpeedWare-Universal-Ignition-4-Position/dp/B07MT2N65B/ref=sxin_16_pa_sp_search_thematic_sspa?content-id=amzn1.sym.fb16fbe4-bf7e-47a2-a56d-1e42bc2dbf4d%3Aamzn1.sym.fb16fbe4-bf7e-47a2-a56d-1e42bc2dbf4d&crid=2YVCM9BRC0ID2&cv_ct_cx=12+v+key+switch&dib=eyJ2IjoiMSJ9.asIY8NLoj-TCFZ_YTP0nF08b0S9C1yKzt0u-L8klVZ7WsMaY7wWzQE9DuiP2e4NY.V3oJ9MWhDsnIwJndqUqUHhNtbhV7PQUxXq0sJnkuuvE&dib_tag=se&keywords=12+v+key+switch&pd_rd_i=B07MT2N65B&pd_rd_r=e9c8cd8a-fb0f-4aaa-b90a-714cbe1b2f2e&pd_rd_w=FZf12&pd_rd_wg=YiayZ&pf_rd_p=fb16fbe4-bf7e-47a2-a56d-1e42bc2dbf4d&pf_rd_r=3R8GPQD3TQ0BW4R7TJXW&qid=1722972707&s=hi&sbo=RZvfv%2F%2FHxDF%2BO5021pAnSA%3D%3D&sprefix=12+v+key+switch%2Ctools%2C124&sr=1-1-6024b2a3-78e4-4fed-8fed-e1613be3bcce-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9zZWFyY2hfdGhlbWF0aWM&psc=1

May not be available on your side of the pond, but you probably have similar available to you. Seems cheap enough to add to the toolbox as a quick & dirty key switch tester. If it works with the cheap one, you can spring for the OEM replacement.