N H 7740 issue.

[acorn]

I am having problems with a new to me 1996 New Holland 7740 (blue roof).
When it arrived the roof mounted radio did not always work.
Fitted new radio.........worked ok....
However it will cut out every now and again...
I have lifted the access panel off the roof and can only get 3 volts from the permanent live feed to the radio.

It looks like others have had an issue, there is another wire (not live) fed up the cab B pillar heading to the battery. It is not connected to the battery.

Has anybody had this problem before...?

Tia acorn.

 

[forblue]

Is the radio losing signal or power if it's power then disconnect perment live and fit the other wire straightr to battery if that works then yes problem is original live feed give me awhile and i will tell you what to look for.

 

[acorn]

.....radio not losing signal....just won't turn on
Fault is intermittant....
Any help gratefully received..

 

[335d]

What is your 3volts referenced to? Negative on the battery or a ground somewhere on the cab. Could be either a ground wire broken or a live feed problem. if you haven’t already, check the cab ground sraps and connect a wire to the battery negative and measure the voltage between your radio wire and the battery negative. I don’t have a wiring diagram to tell u what wire colours to check.

 

[acorn]

335d.
Fly lead to the battery negative, multimeter gives 3 volts to the permanent live at the radio and 12 volts to the switched live....?

 

[Mur Huwcun]

The permanent live is only a memory for the radio to keep your channels etc, as a quick bodge join the yellow and red together to feed both off your ignition feed. If your problem dissapears then just rig up another fused permanent live from wiper motor or interior light etc. We used to fit all radios to new tractors and one cab range didn't have a permanent live supply, tapped them all into the interior light.

 

[acorn]

The permanent live is only a memory for the radio to keep your channels etc, as a quick bodge join the yellow and red together to feed both off your ignition feed. If your problem dissapears then just rig up another fused permanent live from wiper motor or interior light etc. We used to fit all radios to new tractors and one cab range didn't have a permanent live supply, tapped them all into the interior light.

...sounds like a plan.

I have just opened the loom going down the b pillar and it's showing 3 volts there....

 

[forblue]

Here is wiring for radio

 

[335d]

335d.
Fly lead to the battery negative, multimeter gives 3 volts to the permanent live at the radio and 12 volts to the switched live....?

sounds like earth is ok then. its an easy thing to miss, chasing for a dodgy supply cable when it is the return that’s faulty.
as mentioned above, the permanent live is for storing the stations, but it is annoying if it’s not there.
I suspect some corrosion in a plug or loose connection somewhere. If you decide to use the wire that is to the battery, be sure and add a fuse.

 

[acorn]

335d.
I think it is better for me to take another permanent live from the beacon switch.....that way it should be fused anyway...?

 

[Mur Huwcun]

335d.
I think it is better for me to take another permanent live from the beacon switch.....that way it should be fused anyway...?

Try a temporary one from the beacon, I've seen radio's affected by switching the beacon on due to current draw emphasising a weak earth connection somewhere else!!

 

[acorn]

Try a temporary one from the beacon, I've seen radio's affected by switching the beacon on due to current draw emphasising a weak earth connection somewhere else!!

............ your fears are correct, switching the beacon on disabled the radio........now trying the feed from the interior light....

 

[Mur Huwcun]

............ your fears are correct, switching the beacon on disabled the radio........now trying the feed from the interior light....

Right, have you tried the blower fan, beacon and worklights all on at once? This is starting to point as been mentioned to a poor connection at a multi plug. there’s plugs at front of cab connecting main harnesses to the cab, have you checked and cleaned the main earth for cab, IIRC it’s not far from battery