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Old 11-02-2000, 11:58 PM
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Join Date: May 2000
Location: Scotts Valley, CA.
Posts: 145
OK, since there's so much talk about the different relays on board our wonderful cars, and also talk about "wiring in a relay" when using higher wattage headlamp bulbs, I need to ask the obvious question...

What function does a relay serve and how does it work?

I'll take a ration of muck from the list if it means getting this question answered.

Thanks folks,

Jay Yambrovich
1989 300 E
1992 190-E 2.3
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Old 11-03-2000, 01:13 AM
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JCE JCE is offline
Down to the Wear Bars
Join Date: May 1999
Location: So Kalifornia
Posts: 2,189
A relay is basically a heavy duty switch designed to handle more current than, say, your headlight switch. If I understand the wiring correctly, on many cars relatively minimum guage wire runs to the headlight switch, then to the headlights. This restricts the amount of current that gets to the lights. With a relay, heavy guage wire runs to the relay, then to the headlights. The light guage wire that used to run from the switch to the headlights now runs to the relay, and turns it on as a low current device, and the relay turns on the headlights as a high current device. This allows the headlights to draw the maximum amount of power without cooking the wiring or headlight switch. There is a great discussion of relays and diagrams for wiring at

Hope this helps

87 300E, 65k miles
Smoke Silver
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