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ORIGINAL: mySAVIOReigns
Does anyone on here know where I can find a good reference ..... relays and all that?
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how a relay works is quite simple. it's nothing but an electronic switch.
if you check on the great diagram:
http://www.midnightdsigns.com/james/...lightRelay.gif
at the lower right you'll find the workings of the Bosch relay ...-150
there are 5 connectors. 1 of them is not used (#87A). So forget about this one.
now what you see in the picture is the relay in the position off.
the battery+ is connected to #30
battery- (ground) is hooked up to #85
your light switch is connected to #86
and the connector at the headlight itself is hooked to #87
So let's check on that:
you have + and - on #30 and #85 (doesn't do anything)
as you can see in the diagram the little switch on port #30 is currently connected to #87A (that means you have 12V+ on this one from #30). But as it's not used, forget about it
Now here comes the interesting bit:
As soon as you flick on your headlight switch, you'll have 12V+ on #86. which will go through the coil in the relay causing (with a magnetic field) the switch changing
it changes from #30->#87A to #30->#87
that means you now have 12V+ on #87, (nothing on #87A) anymore. This way your headlight is fed with power causing it to light.
Now you probably think: why all that ????
you could always go:
lightswitch
"Battery plus" ----------------------/------------+
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X (headlight)
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"Battery minus" ----------------------------------+
this is exactly what the older Mustangs are doing. But it has a lot of problems.
a) you don't want heavy gauge wires under dash
b) you run through a million connectors (causing this dim headlight issue)
c) you can properly separate the switched circuit from the powered (working) circuit
this way your the headlight gets the power directly from the selonoid without haveing t0o bother through firewall, dash, etc ....
probably a cause for headlight switches to give up constantly
hope that helps ...