Fuel/Temp Guage

I have the stock 1972 Guage set up. Both my Fuel and Temp guages are not working properly. At this moment when the engine temp gets warm the needle barely moves off the rest position. And on the fuel side when I fill the tank it only shows a max of just under 3/4 tank. Its almost as if both guages became uncalibrated so to speak. There have been times where both needles pegged as well, but that hasnt happened recently. I need someone point me in the right direction with ideas to start checking. I am guessing its something behind the dash, as both of the guages do the same thing at the same time.

 

I'd check the grounds. Most electrical problems like this seem to be due to grounding issues.

 

The gauge system uses a voltage regulator which drops from 12v to about 5v for the gauges. Sometimes you can see the gauges pulse when they move up and this is the action of the gauge regulator. Not to confuse this with the alternator regulator. On some systems the regulator is built into the fuel gauge so you cannot see it. Other systems have it mounted on the back of the dash. It will be a small rectangular silver metal can with two terminals. One is power in and the other to the gauges. Because you said your gauges had pegged at one time, I suspect this is the culprit. HTH

 

http://www.jeepfan.com/tech/CJGaugeTech.php

this site helped me out so much with my issues. i hope it can help you as well.

 

Actually the regulator just shoots out 12 volt pulses. It's just VOM at that time were only able to jump up to about 5 volts because they were too slow in responding. These regulators worked no mater what voltage, polarity, temperature. They were pretty neat in design.

Their weak point was the ground. If you lost the ground the regulator would stop working and supply full power to the gauges causing them to pin. They could even burn out your fuel sending unit if the tank was full.

Maybe some of these articals can help, they are mostly for the later gauges used from the mid 70's but other than the external regulator the basics are the same. If yours have the internal regulator in the fuel gauge then these will be quite helpful.

Click Here for basic Gauge instructions
Click Here for Quick Facts about CJ Gauges
Click here for quick test on CJ Gauges
Click here for CJ Gauge Description