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One isn't a relay at all Posted by Ari [Email] ![]() ![]() In Reply to: Difference between the head light relay's?, Wido, Tue, 14 Nov 2006 13:31:14 Members do not see ads below this line. - Help Keep This Site Online - Signup |
The headlight relay is a real relay. A magnetic coil switches contacts around. It's got moving parts.
The bulb check relay isn't a relay at all. It's got no moving parts. It has electronic circuitry that measures the current in each circuit going to a headlight filament. If the current matches between matching filaments (left low to right low beam, left high to right high beam), then all is OK. If it detects a current difference, it assumes one bulb is blown, and it lights the pictogram in the dash. It is the solid state version of the old version found in the early 9000's that used current-balanced relays and was quite unreliable.
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