2001 John Deere 790 4X4 Electrical Problem.

Paul5150 · Feb 28, 2017

Does anyone have good electrical diagnosis expertise on an electrical problem I'm having with my 2001 John Deere 790? My engine temperature gauge will not work unless my fuel tank is 1/2 tank full or higher. Once it drops below the 1/2 level, the needle on the temperature gauge drops all the way to the bottom of the gauge and doesn't move. The only thing I can think is causing this is that somehow the engine temperature circuit is being grounded thru the fuel gauge circuit. Any ideas?

beenthere · Feb 28, 2017

:welcome: to TBN

My first suggestion would be look for a copy of the service tech manual, that will have the schematics for the electrical circuitry.
Sounds like you may have a clue with your grounding thoughts.

Plantation Paul · Mar 8, 2017

Sender unit more than likely. Check the resistance with a volt Ohm meter.

joecdeere · Mar 9, 2017

I have a PDF of the tech manual you're welcome to, if wanted shoot me your email

Joe

Paul5150 · Mar 9, 2017

joecdeere said:
I have a PDF of the tech manual you're welcome to, if wanted shoot me your email

Joe

Thanks, I have the repair manual already that includes the electrical diagram. If I ground the wire going to the temp sender unit, the gauge pegs all the way up to hot. If I keep at least a half a tank or higher of fuel in the fuel tank, the temp gauge works fine. I'm thinking that the temp sender unit and the wire are good. I'm leaning towards a problem with the gauge being that its a soldered circuit board that includes all of the other gauges together. The bad news is that I might have to replace the whole instrument panel that costs over $500

Plantation Paul · Mar 10, 2017

Some how I misread your post, sorry. I would check the grounds on the panel, etc. Sometimes a faulty ground can do some strange things.

Paul5150 · Mar 12, 2017

Plantation Paul said:
Some how I misread your post, sorry. I would check the grounds on the panel, etc. Sometimes a faulty ground can do some strange things.

Thanks. I'm trying to gain access to the back of the instrument panel, but I can't get the steering wheel off.