When I respond to a posted question, I try not to do so in a frivolous manner. If I am not sure of the system involved, I take the time to research it thoroughly before providing an answer.
For example; in this case I suggested the use of a diode/jumper modification to provide power to both sealed beams via the normal high beam feed. The required voltage/power rating of the diode was provided - as was the AWG size of the jumper lead.
This was provided as an alternative to the commonly used method of using an independent power source supplied to the lows - via a relay operated by the high beam feed.
There has been some concern expressed that the addition of the low beams to the high beam circuit would place an undue load on the factory wiring. Unless there are some special considerations that I am not aware of, this modification should not present an issue. My reasoning is explained below:
The primary high beam feed in a 1991 R/V with quad headlights is supplied on a 1.0 gauge wire. This is to supply a pair of sealed beams rated at 65W (130W). The addition of a pair of low beams rated at 55W (110W) yields a total circuit load of 240 watts.
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As comparison:
On a 1986 GMC K2500 with quad headlights, when the headlights are in high beam mode all four sealed beams are supplied by a 1.0 gauge wire (same size as the high beam circuit described above). The uppers (high beam filament) are rated at 60W (120W L/R) and the lowers are rated at 50W (100W L/R). This yields a total circuit load of 220 watts.
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Using P = I x E (I = P / E), when in high beam mode - we get an estimated current draw of:
240/12 = 20 amps on the modified circuit of the 1991 V2500
220/12 = 18.5 amps on the OEM circuit of the 1986 K2500
Note: The current draw was calculated using a nominal voltage of 12 VDC. However, under normal operating conditions, the voltage available to the headlight circuits is more along the lines of 13.5 volts.
Using that voltage, the calculated current draw on each circuit drops considerably:
240/13.5 = 17.8
220/13.5 = 16.3
These circuits are protected by a dedicated circuit breaker in the headlight switch. That breaker is rated for 25 amps:
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Granted - the load on a 1.0 wire would be at the upper limit.
But, if that size was good enough for the design engineers who spec'd the wiring on the 1986 K2500 - it should be safe to carry an approximate 10% increase in current flow (in your Suburban).
240/220 = 1.09
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