I'm new here and am in dire need of help. What I have is an 01 3/4 ton that had a 24 valve with a blown motor. I've pulled the 24 out and replaced with a 12 valve, here lies my issues......1 tach doesn't work, 2 alt. Doesn't charge. Any help would be greatly appreciated

 

Did you replace the PCM with a '98 12V model? If not, you will have this type of issue. As I recall the 12V engines read the engine RPM from the crank speed sensor on the front balancer, and the PCM controls the alternator; whereas the 24V engine reads the engine from the cam position sensor. I know you can wire in an external voltage regulator to bypass the PCM controlling the alt, but I am not sure on what you need to do to fix the tach issue.
Hopefully someone with experience with this type of issue will chime in. I have never done a 12V swap yet, although one will be in my future at some point in time...
Good luck.

 

24 valve does use a cam sensor and the 12 uses a crank what I did was get a kit. From destroked that bolts on the balancer that has a two wire sensor my problem is hooking this sensor to the existing wiring

 

Maybe if you ask in the conversions forum, someone else who has done the conversion can give you some pointers. you will probably get better exposure there:
Diesel Engine Conversions - Diesel Bombers
I wish I could be of more help...

 

Well thanks just the same do appreciate any help or advice

 

u need an adapter for the cam sensor like they use for p-pumping the 24v trucks

 

Got one from destroked with a 2 wire. sensor tach will pickup for about 20 seconds then goes to nothing I'm beginning to be at a complete loss here