Wiring problem on Hymac 580 C

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strontium90
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Wiring problem on Hymac 580 C

Post #1 by strontium90 » Wed Jan 25, 2017 5:42 pm

I wonder if anyone could advise me...Our Hymac starts ok but none of the gauges work (temp fuel etc)...I have removed the control panel and it looks like someone has bodged the wiring, hence the diagram in the workshop manual isn't much help....I have a feeling it's a bad earth but I notice a lot of wires have been cut/disconnected...what colour is the main earth that feeds the control panel and gauges, and where does it connect to first (the one that comes from the regulator)...the white wires (earth) jumping between the gauges seems to be intact, but I am hopeless with electrics...

Any advice would be much appreciated...Thanks in advance..


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Re: Wiring problem on Hymac 580 C

Post #2 by Jeremy Rowland » Thu Jan 26, 2017 8:47 am

Hi Alex, electrics is not my strong point; I will post a copy of the 580C wiring diagram so perhaps somebody else can point you in the right direction.

Jeremy


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Re: Wiring problem on Hymac 580 C

Post #3 by Jeremy Rowland » Thu Jan 26, 2017 8:49 am

Try again; this should be a bit bigger :doh:

Jeremy


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Re: Wiring problem on Hymac 580 C

Post #4 by strontium90 » Thu Jan 26, 2017 10:41 am

Thanks Jeremy...I have this diagram, but I'm afraid it's gobbilty gook to me...I will leave it for now as at least it is starting and charging...will have another go when it isn't so cold and I have more time..Cheers though
Alex

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Re: Wiring problem on Hymac 580 C

Post #5 by FOWLER MAN » Thu Jan 26, 2017 4:24 pm

Hi,
It's many years since I had to play with one of these and I don't remember too much detail.
Is it only the gauges that don't work :?: What about the wipers, heater and horn :?:
The gauges are both fed from the same fuse. I expect that you have already checked the fuses but have you checked that you have a live feed to the fuses. The fuses take their feed from the ignition switch. The connection on the switch will probably have multiple spade connectors on it.
Are you sure that the White wire connecting the gauges isn't the live feed :?: :?: The gauges earth through the temperature and oil pressure senders.
I see in the diagram posted here that they have used White for the live feed to the ignition switch, so that colour code probably continues right through.
A good place to start would be to get a meter or test light and check continuity between the ignition switch and fuses and from the fuse to the gauges. If there is a break in continuity it may be easier just to run in a new lead in place of the original.
Let us know how you get on.
Fred


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Re: Wiring problem on Hymac 580 C

Post #6 by strontium90 » Thu Jan 26, 2017 5:49 pm

Thanks Fred...I will get a look in a few days...busy with hedgecutter at mo...yes, it is just the gauges...the amber light works, and bizarrely enough the horn...I will wait until a good dry day and have plenty of time
Thanks
Alex


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Re: Wiring problem on Hymac 580 C

Post #7 by strontium90 » Thu Mar 07, 2019 11:09 am

It has taken me a while to get round to this, but as I am recovering from an operation, I.ve had some time to get on with it...I will update how I have progressed.

I did as Fred suggested and found that the white wires were the live, in the control panel, and that they feed fuse two (2nd from left) on the control panel and from it, via a green wire, feed the temp gauge, fuel gauge and the ignition light. There was 12 volts going to all THREE gauges. The 1st gauge is engine hours, fed from the 1st fuse on the left and there was a black earth bridging all three gauges. There doesn't appear to be a "cold start" and I don't think Ford engines had one anyways. Thus the workshop manual is useless for the wiring.

I seen this earth was connected to the upper front cab roof but was badly deteriorated so I replaced this earth and , voila, all three gauges sprang to life.
The engine hours and temp gauges are working normally but the fuel gauge is registering as "full". The tank is about 3" from the top but I thought I would check the sender feed anyway.

A green and black wire feeds to the fuel sender, accessed in the battery compartment. I checked that the post on the gauge for this wire is putting out about 4volts carrier current and it was the same at the spade where it connects to the sender. So the continuity seems fine.

However, when I had this wire to the sender disconnected, I noticed that the gauge still read full. If I earth it to the battery, the gauge shows empty so I assume that the sender has a float, which operates a simple potentiometer, which as the fuel level decreases, lowers the float and creates less resistance to the 4volt signal to earth and thus lowers the level on the gauge.

My question is this:- Does the sender unit earth by contact with the chassis of the fuel tank or does it need a separate earth? If someone could look you will see if the sender is connected by one or two wires.
I don't want to remove the top of the fuel tank to see if the float is stuck yet, until I know more about the wiring.
Also, is the sender unit the same as for another vehicle (e.g Landrover) so it would make finding a replacement easier?
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