Re: Educate me: What is the pupose of cab roof marker lights?
 

Don't think it would have been built with them as standard but probably would have had them added to meet regulations somewhere in its working life.

67MY was a transition year for lighting and the factory pretty much built to the federal minimums that soon changed. Many of the heavier trucks still only had a pair of roof marker lights if that. There is no indication in what I just went through in my 67 docs that the five roof clearance lamps were anything but an option (RPO U01). However it is very clear about the positioning with a dimensioned diagram. Below is a brochure clip showing a factory platform/stake dually without markers or even the bed clearance lamps only reflectors. Granted it is artwork and subject to some variations.

Re: Educate me: What is the pupose of cab roof marker lights?
 

I'll further simplify...An option till '69 when they became federally mandated

Re: Educate me: What is the pupose of cab roof marker lights?
 

Are these the earlier style shown on this 1/2 ton 72 GMC? Aftermarket?

Re: Educate me: What is the pupose of cab roof marker lights?
 

I'm ordering a set for my 67 c20 and my 72 c10. The new 07+ 2500 ones.
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Re: Educate me: What is the pupose of cab roof marker lights?
 

These seem correct for this 1971 GMC.....cool truck and for sale (not mine)