[V8] Remoting the Headlamp Sensor ModuleforHeadlightRelayUpgrades

Buchholz, Steven Steven.Buchholz at kla-tencor.com
Thu Nov 10 20:42:29 EST 2005

... if you assume that there is a fairly linear relationship between
overall voltage drop and the length of the wires, you'll find the
longest wires go from the headlamp sensor module to the lamps at the
front of the car.  If one of the reasons you're going for the relays is
to run higher wattage bulbs it compounds things all the more ... so from
my POV I'd say there is little to no value in installing the headlight
relays in the cabin and using the factory wires to the bulbs ...
*especially* since I think the only reason we're talking about this is
to figure out something that allows the headlight bulb monitor to

One big benefit of adding headlight relays and installing them under the
hood is that you get your supply voltage from just about the best place
... right on the high current connection at the alternator.  You can run
a high current wire to the headlight relays (fused of course!) and
shorter wires to the headlights proper.  I don't remember the numbers,
but I'd imagine you could see nearly 2V increase in the voltage at the
bulbs this way.  

I don't know that it has yet been a problem in V8s ... but on some of
the older cars the headlight relay box is also a handy place to locate a
load reduction relay for the starter solenoid.  On the I-5 turbos the
starter can get heat soaked, and that combined with a large voltage drop
in the path to the solenoid creates a situation where the solenoid won't
pull in when attempting to start a hot engine.  

Steve B
San Jose, CA (USA)
> I think you missed what I was saying here...leaving the light
> control module with stock wiring to the headlights and upgrading the
> supply wire to the module.  This would not put it series with the
> relay coils, it would leave it factory wired.  The relay coil(s)
> would be connected to the "old" original supply wire from the switch
> and ground.
> I was under the impression that it was the supply routed through the
> stalk mounted switch that was voltage drop culprit, not the wire
> from the light control module to the headlight. I was suggesting
> running a single large gauge wire from the battery to the footwell
> and relaying it there.

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