Instrument cluster electrical question 75cj5

Last week I noticed that I had lost both temp and fuel gauges. While running, fuel always reads empty, temp always reads cold (as they would in the ignition off position). With a test light connected to ground and the ignition "ON" I get a pulsing light (as if reading through a flasher) at the back of the guages. Anyone know what's up? Sorry, I don't know if I have given you guys enough information to answer the question?
Thanks in advance...Mike

 

the reason for the flashing/pulsation is the voltage to the gauges is being reduced and controlled by a voltage regulator built into one of the dash gauges, can't recall which one, (ie. 12 volts down to 8-9 volts) Iwant to say the dash fuel gauge though. 12 volts would come into the gauge with the regulator and the lesser amount would come out and be carried over to the other dash gauge; there should also be a connector bar (insulated) the connects the 2 gauges together.
It would probably be quicker/easier to temporarily ground each sending unit wire at the sending unit; if the dash gauge is functioning correctly, the needle will slowly go across the full range of the gauge; this of course meaning that the wiring and such are all okay
check for power out at your temp sending unit wire on the engine; with key on, you should get the same pulsation; if not, no power or bad wire or bad voltage regulator; if you do have pulsation, ground the wire temporarily, and the dash gauge needle should move across the face of the gauge; if not, possible bad gauge.
loosing both at the same time might mean a bad dash gauge, whichever one that has the voltage regualtor built into it

 

Thanks for the info Jim. I will trouble shoot tonight after work. I didn't know about the regulator in the guage and I did see the connerting bar back there. I'll check the temp gauge wire at the sender first.
Thanks again......Mike

 

Regulator is in the fuel gauge. 12 volts comes into one of the three terminals on the fuel gauge.

the other wire coming off of the fuel gauge goes to the sender.

the third terminal has a wire strap that goes to the temp gauge.

If you want to check this out, get the engine warm, and fill the tank with gas.

Using a test wire, connect the terminal that the 12 volts comes into the fuel gauge to 12 volts from a known good 12 volt source (battery??) If the gauges deflect then you either have a defective fuel gauge (regulator side) or a break in the connection between the IGN terminal on the ignition switch.

Don't connect the 12 volts to any other gauge terminal except for the one that has teh 12 volts coming in. On some jeeps I've seen this wire is actually two green wires. 12 volts coming in, and the second green wire passing the 12 volts on to something else.

 

That other wire is actually the feed to the ignition coil wire. And it is green on my 67. I know because I was doing some rewiring this weekend, and wondered where that other wire from the fuel gauge went....it shows it in the wiring diagrams in the FSM also. Or in other words there are actually 2 wires connected to one eyelet on the fuel gauge, one continues on to the ignition coil, and the other goes to the ignition switch to pick up power (12volts hot in run position).

 

Thanks guys, for all the help. I will report back when I trouble shoot it this weekend. Until then, I'm keeping a close watch on the odometer. She's my DD for now. Great site!

 

I am having the same problem with my 75. I know the sending unit is good (just replaced it). Had the dash out checking the wiring. I did pull the fuel gage itself. A wire was fried inside. Replacement time. Mine is also DD. Thanks for the info. This will be a great help. walt