SL55 Interesting Coolant Pump Wiring

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Active Member
Oct 21, 2018
Noticed that I had the usual symptoms of a broken/weak coolant pump (had the same with my CLS55) so ordered a new coolant pump and got around to fitting it today.

Found out that the Bosch pump had already been fitted but the wiring had been changed! The original wire had been cut at the plug and a new wire has been spliced into a loom, I have no idea why. I traced the wires back up to the loom and found this under the wiring compartment in the engine bay...any idea why anyone would have done this?

What's the best way to test if the pump is receiving power? On my CLS55 it would run for about a minute or so when ignition was switched on but this doesn't seem to be happening with the SL? Is it meant to? I want to make sure that the wiring is fine before fitting the new pump. Any ideas.....?


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Update, returned all wiring to stock and coolant pump is now working perfectly.

I suspect that someone previously tried to wire up the pump to ignition but didn't really know what they were doing

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