Most harnesses that I've seen come with the amp turn-on lead. Something to be mindful of when buying a harness is that most mid-90s on up cars used the same ISO connector only difference being that ign and constant power are reversed on some applications, so make sure that the one you buy has them correct for MB or will have to swap leads.

These following two are correct.

https://www.amazon.com/dp/B0007WRQG2/ref=psdc_15729931_t3_B0002BEQKM

https://www.amazon.com/Metra-70-1784-Wiring-Harness-Volkswagen/dp/B0002BEQKM/ref=pd_sbs_107_2/140-2506849-2013548?_encoding=UTF8&pd_rd_i=B0002BEQKM&pd_rd_r=a9e101b7-e85e-4939-9d2c-e24f892ae8a8&pd_rd_w=99y9r&pd_rd_wg=Gl9ap&pf_rd_p=52b7592c-2dc9-4ac6-84d4-4bda6360045e&pf_rd_r=0MFXJG9NERFBR984RMV8&psc=1&refRID=0MFXJG9NERFBR984RMV8

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