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Re: Lighting questions
I've taken the liberty of copying the text below from Scott Mockery's web
site (thanks Scott) at
Note the table re: Operating Voltage vs. Luminous Intensity.
It indicates that a 10% voltage drop results in a 33% drop in luminous
Did you ever check the voltage of a flashlight battery that appears to be
dead? You are usually throwing it away by the time it drops to 1.3 volts.
As Bob Meyers says...do the math. It doesn't take much resistance to cause
a significant voltage drop.
Scott Mockery writes:
Regarding the idea to install High Wattage 9004 Bulbs in the lousy OEM
headlights found in the 1986-88 5000T/Q and in the 1989-91 200T/Q. Don't
Many years ago, before I knew any better, I installed the aftermarket
70/80W 9004 halogen bulbs in my previous 1986 5000CS Turbo which "seemed"
to improve the lighting coverage over the standard 45/65W bulbs. At the
time, I also installed relays to improve the amount of voltage at the
headlight bulb and to avoid toasting the stock headlight switch
connections. The headlight switch connections can be toasted while using
the stock 9004 bulbs, see information in the next section for more details
on this problem. Before I installed the relays, I measured a 1.0 volt drop
from the battery to the stock 45/65W Headlamp bulbs. The factory wiring
setup runs the full current to the headlamp bulbs through the headlight
Hella published the following values for "Luminous Intensity" which point
out how critical it is to get full battery voltage to the headlamp bulbs.
100% voltage is considered 13.5 Volts for the 12V system. Using relays can
help even the marginal stock headlamp performance by providing full battery
voltage to the light bulbs.
Operating Voltage Luminous Intensity
The High Wattage 9004 bulbs were more trouble than they were worth,
they only lasted 4-6 months and they would burn up the stock 9004
connectors unless you beefed up the wiring or purchased the high wattage
9004 connectors. Finally, one day after using the high wattage bulbs for
about a year, and yet another High Wattage 9004 bulb burned out, I replaced
it with the stock 45/65W 9004 bulb I had for a spare.