ahh, sorry I wasn't paying enough attention on your other post - GMC is the answer
I was thinking Chevy - I believe those were the beginning of the "tell tale" lights, a Blue Chip [5-9 series GMC] truck owner will have the answer, your light truck probably didn't get the actual lights .... and as your signal setup is add-on, they're not related .... maybe add the GMC detail to your post title [click 'Edit' under your first post] here to attract the right attention
also
check here, about halfway down is the 5-9 GMC shop manual and a Hydramatic manual you'll find useful
Bill
