Chicken switch

[danmetallic]

The PO of our van had an illuminating chicken switch installed that operates the low setting of the radiator fan.

A strange thing happens though. When in the off position the switch with slowly light up, getting gently brighter as the van travels faster down the motorway. Then dim again as we slow down. Very odd.

Any idea what might be happening?

[itchyfeet]

Does it happen if you rev the engine or just by van speed
?
I wonder if somebody has connected the green coil neg/ tacho to the lamp/LED thinking green is earth.

if its just van speed and not engine it must be voltage produced by the fan rotating, a motor and a dynamo are very similar.

[marlinowner]

Sounds to me as if the fan is windmilling at speed and acting as a generator. Lamp in switch is connected between fan and ground.

[CovKid]

Harness the power and take the load off the national grid.

[danmetallic]

Guys that makes perfect sense! Definitely only with speed. Should feed it back into the battery