Intermittent gauge problem 76 FJ40 (1 Viewer)

[shmukster]

Been having a persistent but intermittent gauge problem on my 76 FJ40. It has a stock instrument cluster, stock fuel tank and correct (original) temp sending unit. The problem is that at times (and currently) neither the temp gauge nor the fuel gauge read at all. At times they both work- but motre often than not they are not working.

I looked at the back of the cluster and saw that there was a terminal common to both gauges but not connected to the round pin connector, figured it was a ground. Ran a ground wire from the gas gauge terminal that was in common with the temp gauge and that did not help. Can anyone shed any light on this for me? I'd love to have thegauges working again and am getting tired of pulling the cluster out. HELP! Thanks, Gary S (Shmukster)

 

[rainerius]

Been having a persistent but intermittent gauge problem on my 76 FJ40. It has a stock instrument cluster, stock fuel tank and correct (original) temp sending unit. The problem is that at times (and currently) neither the temp gauge nor the fuel gauge read at all. At times they both work- but motre often than not they are not working.

I looked at the back of the cluster and saw that there was a terminal common to both gauges but not connected to the round pin connector, figured it was a ground. Ran a ground wire from the gas gauge terminal that was in common with the temp gauge and that did not help. Can anyone shed any light on this for me? I'd love to have thegauges working again and am getting tired of pulling the cluster out. HELP! Thanks, Gary S (Shmukster)

That is why I am saving to get me those damn Auto Meter gauges. The stock ones just gets crazy from time to time.

 

[subzali]

My '77 does that too and I've scratched my head over it for 3+ years. Haven't been able to search up a solution here on MUD either.

Looking at the wiring diagram, it would seem that there is an intermittent loss of power just after the oil pressure gauge. Unfortunately I don't know what that exactly looks like with the round pin connector and the circuitboard on the back of the gauge panel. I've swapped instrument clusters too and the problem was still there, so I'm pretty stumped.

 

[ColonelMustardFJ40]

Well, looking at the OEM wiring diagram (not the back of the cluster) I am surprised that if your fuel and temp gauges don't work that your oil pressure continues to work. Basically these all have common +V supplied on one side of the gauge and then each gauge has an individual wire running out to the associated sensor and then at each sensor the ground is provided completing the circuit. So, current needs to flow from the +V common point, through the gauge (needle deflection relative to current flow), out to the sensor, into ground and back into the source (battery). I am not sure where you hooked up the ground on the cluster that would help your diagnosis, especially if you hooked it to the common point for all of the gauges as this should have blown the 20A fuse for the heater (based upon the schematic I am looking at - 1976 FJ40 USA). So I would make sure that you have good connections and +V (battery voltage) at the common point with the ignition ON and that you have good continuity between the individual wires and the sensors and that some portion of the +V can be measured at the sensor point. Check for dirty/oily/frayed connections. Hope this helps.

 

[softdrinkviking]

happened to me and...

My '77 does that too and I've scratched my head over it for 3+ years. Haven't been able to search up a solution here on MUD either.

Looking at the wiring diagram, it would seem that there is an intermittent loss of power just after the oil pressure gauge. Unfortunately I don't know what that exactly looks like with the round pin connector and the circuitboard on the back of the gauge panel. I've swapped instrument clusters too and the problem was still there, so I'm pretty stumped.

both the temp and fuel sensors connections on my cruiser have a tendency to shake around and cut out sometimes. i replaced the fuel sensor lead because i needed to know how much gas i have, but i still haven't replaced the connector that slips over the temp sensor because it's original and it's usually fine.

if this is your issue, it's easy to check because all you have to do is snug up the wire connector on the sensor end when it goes out.

 

[edwjmcgrath]

Another possibility. The fuel gauge has a voltage regulator built into it that feeds 7 volts to the fuel and temp gauges and sensors. If that regulator fails so that it does not feed the 7 volts, those two meters will not work.

 

[LocoJR]

This seems to be a common thread to gauge problems. The 7v regulator seems to be a wire resistor around a bimetal strip in the fuel gauge. Mine ('74 FJ40) appears to have a break-contact if it draws too much current and heats.

This is besides the bimetal for the actual fuel gauge. If there is a short in the fuel or temp, or the circuits, it would cause an intermittent problem when the 7v regulator bimetal heats up.

Can somebody confirm?

 

[LocoJR]

My mistake. The regulator should buzz if it's operating correctly, averaging 7v using duty cycle. Look up Smiths Voltage Stabilizer.

JR

 

[PabloCruise]

Another possibility. The fuel gauge has a voltage regulator built into it that feeds 7 volts to the fuel and temp gauges and sensors. If that regulator fails so that it does not feed the 7 volts, those two meters will not work.

Back to this - has anyone ever found a replacement regulator/transformer to step voltage down to 7v for the cluster?