Is this factory or something added?
 

Hopefully someone can help. Working on the wiring on the 71 blazer and cant find these relays on any of the wiring diagrams. One of them has a black wire that runs to the t350 transmission, I'm assuming this is the back up light switch? the other is a green wire that ran to the water temp sensor. Does any of your blazers have these mounted on the firewall next to the wire harness bulkhead?
Thanks in advance for any insight on this....:chevy:

Re: Is this factory or something added?
 

Part of the transmission controlled spark system? Early emission controls.

Is there a solenoid connected to the vacuum advance on the distributor?

Re: Is this factory or something added?
 

Are you talking about the solenoid on the transmission? Its connected to the manifold vacuum not directly to dist. I cant seem to find a wire schematic to show this wiring layout either? I don't know?:waah:

edit:
Ok, found some details in the original "10-30 Chevrolet Truck Service Manual", kind of hard to make out the wires and routing. I think I have some snipped wires I need to trace back?

Re: Is this factory or something added?
 

Those relays are factory. They are part of a 1971 only emissions system called CEC. In the attached diagram they are labeled Time delay relay and reversing relay. There also was a solenoid attached to the quadrajet that was part of the system. A google search of 1971 CEC will bring up more info on how the system was designed to work.

Re: Is this factory or something added?
 

Thanks JackB, that's the info I was looking for!