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Old 09-07-2017, 02:11 PM   #4
_Ogre
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Join Date: Jan 2012
Location: Motown
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Re: Question About Interior Cab Light - 1959 GMC

the dome light in most gm precomputer vehicles has 12v+ to the bulb and grounds thru the headlight switch
cars also ground thru door pins, while our trucks don't have door pins the switch is designed for grounded dome light

this is the task force headlight switch



old trucks had pretty basic wiring, base truck had no fuse panel, no radio, no heater and vacuum wipers
all lighting on the truck was protected by the headlight switch, the small fuse is for instrument panel lights
the rest of the lights are protected by bimetal strips you see on the headlight switch picture
when they had an overload the bimetal would heat up up breaking the points, cool and restore power
this prevented total loss of headlights while driving, the headlights will flash

if the truck was ordered with a heater it will have an inline fuse
as accessories were added: radio and electric wipers, gm added a 4 fuse panel behind the headlight switch
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