Non starting

[Jeepman272]

Hi,
Drove my GMC at the weekend, not an issue. Parked her up, came to start her today and nothing, dash instruments on, lights work but nothing at the starter. Checked the 6v battery and all ok. Took the solenoid of the starter and it tests ok. whilst it was off I put the battery lead onto the starter direct and it turns over!!
My guess was it must be the solenoid but it looks good so took it to an electrical engineer and he said it's fine.
I put it all back together and noticed when I press the starter pedal, the fuel gauge drops from half full to empty (never noticed before so could be normal), and I can hear a slight humming.
When I find someone to help me i'll get them to press the starter whilst I am under the bonnet, but has anyone had similar issues?

Cheers,
Alistair