Glow plug dash light and Glow plugs not working

[200mph]

The glow plug relay load is heavy wire to a 50 amp fuse. The relay closing wire is on a 5 amp fuse in the schematic of my previous post

If the wire is similar to my L4740-3, the wire diameter from the 50 amp slow burn fuse to the relay socket is fairly large (guessing 12 awg or metric equivalent). The wire from the relay output to the GP connector located near the oil filter is only approximately 16 awg (at largest). From there to the GP buss bar it is back to the larger size. Not certain why this is the case.

The WSM wiring diagram suggests the wire size between the Relay feed and output are the same, but that is not the case on my tractor. Just looked at it yesterday to help the other thread (L3240 won't start when cold) going on about GP operation.

FWIW it is very easy to test the GP voltage and supply time using the single wire connector assuming this model is similar. Disconnect connector and probe for voltage when the key is turned on. If battery voltage at this point everything is generally OK. (Note: GP can not be attached when testing voltage on GP buss bar. Voltage will read very near 0 volts)

Included pictures of the GP wire connector near oil filter and of the slow burn fuses. Please keep in mind these pictures are taken on a L4740.

Good luck with the diagnosis and repair.

 

[n4khq]

Thanks very much; very helpful. I will let you know how it goes in a few days

 

[n4khq]

Here is a summary of the glow plug problem. Tractor would not start on cold morning. Checked coolant temperature sensor and it was working. Dealer contacted Kubota Rep and the rep said could try replacing glow plug relay, they had problems with the relay, or try getting a temperature sensor that would send a high resistance for a given temperature or most dealers were adding a manual switch. After 3 days for trying to get the dash off; I just replaced the relay. The morning was 27 degrees, and the tractor started right up.

 

[200mph]

The problem is with the relay supplied by Kubota and the terminal size inside the relay socket. The relay socket is supplied with 3/8" wide female terminals on the power side (high current side of relay) and the relay supplied by Kubota is only 1/4".

The width isn't the issue, but the thickness of the terminal is. The 1/4" male tab has a thickness of 0.030" while the 3/8" male tab is 0.045. This extra thickness allows for a tighter fit within the female terminal.

In my case the detail that creates the spring force was highly fatigued, which I'm guessing was due to high heat from the poor electrical contact and high current of the GP circuit.

I have the details of my investigation on the other tractor web site with photos to better describe what's happening.

Send private email if you want the link.