Factory Tachometer Install for 2.5L Iron Duke?

Rmhavema

Overlander
LIFETIME
CJ-8.com Member
City
Northville
State
MI
#1
I have a '82 CJ8 with the 4 cylinder 2.5L Iron Duke. It did not come with the factory tachometer, but I have one from a donor dash. I am guessing the tachometer is from the 258 or 304. Is there a way to make this tachometer work correctly with the iron duke? Also, would the wiring harness already have the connections for the factory tach? Any help is appreciated.
 
City
Halifax
State
UK
#2
The tacho says what engine its for on the rear of it somewhere and they are specific to the no of cylinders i believe, so unfortunately you will need one from a 4cyl Jeep i think.
 

AK-RWC

Legacy Registered User
SOA Member
City
south central
State
AK
#3
I always check the 258/304 differences by quick glance at the redline: the 304 is 5000 RPM, while the 258 is 4500 IIRC. I'm not sure what the redline is for the 4-cylinders. Either way, as noted above, the OEM tachs are specific to each engine. While the 304 and 258 share the same wiring harness splice (and can be installed in a 258/304 CJ that didn't originally come with a tach without the need for any additional wiring), the tach for the 4-cylinder had its own separate harness. Which means that there's essentially no way to make the tach you have work with your engine.
 

gazzo

AMC Jeep nutjob
LIFETIME
CJ-8.com Member
City
Fremantle
State
WA
#4
My renegade originally had the 4 and when I went to the 258 I just disconnected the tach wires and left them loose then pulled the fat red/t wires apart at the connector and plugged in the 6cyl tacho. I threw the 4cyl tach out at some point only to be told later that it was good for the V8. Dunno if that's the case though.
 

Rmhavema

Overlander
LIFETIME
CJ-8.com Member
City
Northville
State
MI
#5
Thanks all for the help. Turns out I have a 6 cylinder model. I did a little more research myself. According to the Service Manual, it looks like the 6 and 8 cylinder tachs have a black ground wire, orange illumination wire, and 2 red signal wires (one with a white stripe). The four cylinder tachometer has a 3 prong plug with red, white, and black wires. It also has the black ground and orange illumination wire. I found an empty 3 prong plug under the dash, so now just need to find a 4 cylinder gauge..... From what I have read, the aftermarket Omix Ada gauge is wired like the 4 cylinder gauge, but can work with 4, 6, and 8 cylinder engines. Apparently it wires to the negative side of the coil, different from the factory 6 and 8 cylinder models. So, it is not a direct plug in on the 6/8 cylinders. It should work on mine, but I am going to hold out and see if I can find an OEM gauge. Thanks for the help!
 
Top