Did the 5 volt gauge conversion-questions

[Curly5759]

I did the 5 volt gauge conversion to an extra dash cluster I had laying around. I followed the write up on this thread: http://www.ifsja.org/forums/vb/showt...=120103&page=4


I hooked some jumper wires to a battery and used a fuel sender as a variable resistor. Both the oil and fuel gauges worked but the temperature gauge will peg hot even without anything hooked to the gauge.



I took it apart, looked for problems, found none. It has 9 ohms resistance to ground w/o a sending unit attached. The other 2 had about 30 Ohms w/o a sender.


I did remove the noise suppression jumper from the circuit board.


Do I have a shorted temp gauge or is there something else going on here?


Thanks.

[tgreese]

Look at the diagram on page 1L-44 of the 1979 TSM on the Tom Collins site. https://oljeep.com/edge_parts_man.html

When you remove the radio noise suppressor, that interrupts battery voltage (we'll call it 12V) to the temperature gauge. The internal CVR is connected to this 12V in and the A terminal on the temperature gauge. You have disabled the CVR by removing the radio noise suppressor.

Now you supply 5V from the regulator chip to each of the A terminals (A1, A2, A3) of the three gauges: oil, temp and fuel. You can supply 5V to any of those A terminals and it will be conducted to the other A terminals by the traces on the circuit board.

Measure with your multimeter. You should have 5V at each of those points. Each gauge also has a sensor - the S terminal - which is a variable resistance to ground. Page 1L-43 shows the resistances that you should have to read each of the values on the gauges. If you ground the S terminal of the temperature gauge, it should peg to full hot. If you leave the S terminal floating (not connected to anything) it should read fully cold.

If you don't see this, then you either have a bad gauge or something shorted out. Do not short out the temperature gauge for more than a moment, since a short conducts full current through the gauge and will burn it out shortly (pun).

[Curly5759]

Tim, thanks for the reply. I do have 5 volts at all 3 gauges, and since the gauge pegs with no ground, I am going to guess that it is internally shorted or I didn't get it isolated from ground when I reinstalled it. ( I took it out to inspect it and try and learn how it works. )



I'm going to remove it again and make sure it isn't shorted internally, then put it back in and try again. This is just a test before I do the actual conversion to my working dash.


Edit: Thanks for the link, I have the 1980 and 82 FSM manuals here that I have been referring to.




Thanks again
Tim