Posted on Jun 8, 2012

When the driver depresses pushbutton switch S1, timing capacitor C1 charges to 12 V and turns on transistor Q1, which drives power transistor Q2 into conduction. This, in tum, energizes the relay which has its contacts connected in parallel with the headlight switch. The relay will stay energized unW C1 discharges to the Q1 tum-off level. The lights-on period is determined by the value of C1, R1, and the characteristics of transistor QL With values chosen on the schematic, about 60 light-on seconds are provided.

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C1-500 uF electrolytic capacitor, 15 VDC or better $1-SPST pushbutton switch, normally open 01-NPN transistor, 2N1302, HEP-641 (time-start switch) 02-PNP, transistor, RCA 40254, HEP-628 Misc-31/4-in. x 21/e-in. x 15/e-in. case, 1-amp SB R1-3,30D-ohm, 1/2-watt resistor fuse with pigtail leads, #14 wire, hook-up wire, R2, A3-560-ohm, 11.2-watt resistor printed circuit material, hardware, solder, etc. AY1-Aelay, DPDT, Hl-amp contacts, 12 VOC coil resistance-at least 100-ohms, Potter and TAB BOOKS Brumfield type MA11D or equiv.

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