it's a 1980, 116 chassis. 116 3.5 litre motor. Just to clarify; I can hear the starter solenoid clunk, (though after 2 goes it gives up) but the starter motor itself does not engage.
I tried jumping it with my 124 diesel, but didn't help (though my jump leads aren't the best...)
The radio still turns on, exterior lights are dim and dip when trying to start.
Foxing me as it was fine less than 2 weeks ago.
Only service items I've changed are fuses and spark plugs.

This car and chassis is new to me, being used to the 124 before- whereabouts is the starter located on these cars?

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1993 320TE M104
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past:

1983 230E W123 M102
1994 E300D S124 OM606 (x2)
1967 250SE W108 M129
1972 280se 3.5 W108 M116
1980 280SE W116 M110
1980 350SE W116 M116
1992 300E W124 M103
1994 E280 W124 M104
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"music and women I cannot but give way to, whatever my business" -Pepys