I'm putting a tach in my 91 5.8 and I have always hooked the green rpm signal wire to the negative on the coil...which on these trucks should be the orange wire on the bottom of the coil, right?

I'm thinking the rpm gauge is faulty.
What do you guys think?

 

The tach wire is behind the cluster too, even if you don't have a tachometer. I don't have my diagrams in front of me to give you the colors.

 

I was hoping you would chime in! Ya this truck doesn't have the factory tach and I wasn't sure if the wire is there like the 92-96 trucks so I figured I would throw this little 2" tach in it but can't get the needle to move!

When the key is on I have power to light my test light on both the coil wires in the pic.

The tach has to be faulty!

 

Coil negative is the tan/yellow wire.

 

Thanks Sean. Ya I second guessed my self over and over and then returned the tach and installed the new one in the parking lot...it didn't work either!!
So I went back in and got the bigger tach that seemed better quality and again installed it in the parking lot and it worked!
The lady at the store said must be a bad shipment.

 

Yeah, that would throw me off too.

 

You didn't get one of the small Equus tachs from Canadian Tire did you? The small 60$ ones only work for certain applications we found out, its not just you.

 

No the tach that wouldn't work was the small LED tach from princess auto.

 

I haven't installed those ones before, but may be a similar problem with some of the tachs not being able to get a signal from the coil like the ones I have tried.

 

Ya I was thinking that as well. The tach I ended up getting is much better quality and I actually had this same tach years ago in a old 4x4 and it worked for years with no problems.