to accomplish Willy's idea is to use a Hall Effect (HE) device. This device, for those who may not know, produces a voltage output proportional to the current flowing 'by' the Hall Effect sensor. You don't have to break into the wiring to sense the current flowing in the fans.

So use of the HE sensor and a few external parts (LED, etc) will show as a proportional glow in the LED as the fan(s) change speed. Nice device if it can be done cheaply.

I've never seen current flowing when an aux fan 'dies'. When they fail to 'turn', with eveythjing else being ok, you'll find that the brushes are 'bad'. Somtimes giving the fan a 'bang' will start it going.

If the controlling relay's contact 'welds' which is a realistic failure mode, the fans will continue to turn. But the LED will show that.

I'm thinking more about it . . . . . . .

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Regards . . . . JimF
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'94 S500 Cpe

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