Mahindra Bolero SLE — About speed of vehicle when lights on

Address:

Muzaffarpur, Bihar, 842001

Sir,
I have Bolero SLE, Reg No...0442, The speed of vehicle started decreasing when lights switched on even on full accelerator. I have visited two available service centres here in Towns and also to local mechanic. No body has recognised the problem, if you have any clue, please advise accordingly. My email address is [protected]@gmail.com