Tach help, its easy..

[Lineman]

What is this blue wire all about??

 

[BeepBeepRR]

Look at the lower section of this page. I assume you have the Rally cluster. Blue with the angle plug goes to the tach. Orange is the light bulb holder for the tach. The grey wire is the tach signal from the coil. The blue wire then goes to a keyed source. But in this diagram it says use the yellow 3 hole plug. Usually a hot off the fuse block. Orange will go to a 3 hole wiring plug.

 

[Nacho-RT74]

on that pic the blue wire terminal is not really accurate for 71 and lates models. Would require to use a bullet kind terminal like the orange one. It seems to be more like an earlier model, to be spliced straight to the fuse box ( it seems to be a "piggy back" terminal ).

however you could run it straight to the fuse box panel, in front, into an embossed male terminal ACC source. But that's not a fuse source.

about the coil wire
71 and 74 uses one cavity free of the bulkhead terminal. 71s into the engine harness block, 74s into the NSS harness block

72 and 73 uses the grommet, requiring to drill the firewall

The orange wire for socket wouldn be used. Rallye harness already provides that. Either with Clock, Tach, or Oil/gas large gauge, the socket for that location is alredy existant on harness

definitelly, that harness is not accurated for 71 and lates... useable thought

 

[Lineman]

Thanks guys, I should have stated.... I am working on a 69 non rally dash.. I didn't see where to connect it on the back of the tach.. I keep forgetting the tach has to independently powered I put the harness in the car a while back.. I have this to get squared away and connect up the cigarette lighter as that wire doesn't seem to just plug on the pin?? Any ideas there??

 

[Nacho-RT74]

Well, the blue wire will run to the back of fusebox then to the accesories source side and will be stacked with some other terminal.

I can’t tell about light provision for the tach on that harness HOWEVER, still having a clock or a delete plate, the underdash harness should have the socket hanging around for that area. I don’t get the need for the light provision on tach harness yet.