Tachometer Install on 1984 2.3L

[RJMacReady]

Hey folks, trying to install a tach. It's the 4 wire style (power, ground, light, engine signal).

Found a good spot for the ground but none of the diagrams I've found look quite like what I'm seeing in my truck so I could use some help figuring out where to to put the rest. Here's a shot of my fusebox and my coil. Anyone know what I'm supposed to do here?

 

[RonD]

Tach signal comes from Coil "-" so the green wire terminal in picture

You don't want Tach to be "on" when key is off, so you need a 12volt key on wire or fuse
There will be a Red/light green stripe wire that comes out of ignition switch(under steering column) that runs out to engine bay, it has 12v key on
That same Red/light green wire is at the Coil "+" terminal in your picture so you could use the lead you are holding for 12v key on

Ford uses a Light Blue/red stripe wire for dash lights, it comes out of the main light switch, and has dimmer control, you can tap that wire at the switch to get dim-able back light for tach

 

[RJMacReady]

That's very helpful, thank you! Let me make sure I understand correctly. The cable with the plastic connector on it is key-on 12 volt, and the double green on the right side is the tach signal? Does it matter which of the two on the double green that I tap?

 

[RonD]

Yes, use a volt meter(or test light) to confirm 12v on that short wire with key on and no volts with key off, you could use a 5amp inline fuse on your added wire to the tach just because this is a main 12v wire and a short on your added wire thru firewall would be a BAD thing, i.e. melted wires and engine would stop running

And just FYI, that short wire and connector was used for a Radio Noise suppressor capacitor, as coils would cause static on AM stations when engine was running

They can look like this: https://www.fullsizebronco.com/attachments/f-18832-4_20180411220418-jpg.152172/
Or this: https://d3d71ba2asa5oz.cloudfront.net/12006198/images/inl12834_325__1.jpg


No, doesn't matter, you can tap either green/yellow stripe wire to get tach signal, but these wires do make the spark so make sure you don't break their connection to coil

 

[RJMacReady]

Awesome, I'm going to put a fuse in then. Better safe than sorry.

These little plastic taps they gave me with the gauge are junk, I'm going to have to order some in a different style.

I really appreciate all the detail, I knew signing up for this forum was a good idea.

 

[RJMacReady]

Got some T-Tap style connectors in 12 gauge, those did the trick. I tapped the two wires you mentioned and now I'm getting the right RPM readout! Pretty awesome.

I haven't tried to get up under the dash to find that dimmer switch wire, I'll give that a shot tomorrow.

 

[RobbieD]

Two screws will let you will drop the ashtray bracket, where you can pick up the Lt Blue / Red stripe wire for your tach light. It's easier getting it there than at the headlight switch.

 

[RJMacReady]

Trying to get into that ashtray area, I dropped 2 screws from the top of it, but it wasn't coming off. Took some trim off the right and found a third screw.. Not sure if I'm on the right track.

I do see a set of wires back behind the cage though.

Appears to be hold on by a third almost rivet looking kind of thing? Not sure what I'm seeing.

 

[RJMacReady]

Here's a better pic.

 

[RobbieD]

There's a similar screw on the left side; carefully pry the trim off to the left of the ashtray to expose it.

 

[RJMacReady]

Got it all dropped without too much trouble. Tapped the light blue with the red stripe and it's just what I needed. Now I the gauge has light and dimmer function! Thanks everyone, feeling good to have pulled off my first project of this sort.

Really wanted a good view of it right next to the speedometer, so I stuck it on the steering column. I didn't have a hose clamp so I 3d printed one. May rework it so the size is better and I can close it with an M3 bolt or something.

 

[RonD]

Looking good

 

[RobbieD]

Good job; I like how you mounted it!

Also kinda cool how both your red lines are at "55" : )

 

[RJMacReady]

Also kinda cool how both your red lines are at "55" : )

Haha I didn't notice that! Actually, question, how many rpms would the redline be for the 2.3L?

 

[RonD]

I would say 5,000rpm would be Redline for the 2.3l SOHC Lima engine
On 1983-1986 2.3l Max horse power is at 4,000rpm
Max torque is at 2,400rpm

So not many reasons to go above 5,000rpm