I have a '66 f-100.I have put in a new sensing unit and replaced the fuses but still the gauge does not work at all. What else can it be? I have the little round gauge package/speedo. temp gauge also does not work at all. idiot lights for alt and oil pressure work. I replaced the ground wire to sending unit and put anew connector to the sending unit =. the wire looks good to the harnes and is connected to the gauge? I 'm new to this and have no idea where to look next. Thanks for any help.

 

I would check on the little voltage regulator from the back of the speedo. It seems like to me that would be the most likely culprit. It looks like a little box with two small electrical blade connectors coming off of it. I don't believe the idiot lights use it, but the gauges do.

 

thx for the info. do you know if the regulator is readily avalible?

 

You can see from the diag. the CVR unit is also tied into the other gauges, think you will find if CVR unit is faulty the other gauges should also be effected. As Broomfieldbum mentioned possibily the CVR unit. You can test the CVR unit by taking volt meter should fluxuate between 0-9 volts. If the other gauges are working then you may try testing the fuel gauge, disconnect the leads and take a 2D cell flashlight batteries, positive to 1 side of the gauge and the other side of the gauge to neg. side of flashlight. Usually find the neg. side of flashlight is at the on/off button. Anyhow, food for thought?

http://i300.photobucket.com/albums/n...reDiagP5-1.jpg

 

If the ICVR = Instrument Cluster Voltage Regulator is defective, it also affects the temperature gauge.

When this regulator begins to fail, the needles on the fuel and temp gauges do the "hula" as they swing back and forth on their own.

B9MZ10804C .. ICVR (Motorcraft GR508) / Obsolete from Ford / Available from autoparts stores.

Fits: 1961/66 F100/1100 // 1959/66 Galaxie/LTD/Thunderbird / 1960/65 Falcon/Comet / 1962/65 Fairlane/Meteor / 1965/66 Mustang / 1966/77 Bronco.

Take the old ICVR with you to the parts store to match it up. There are other types, so you wanna make sure you get the correct one.

 

Thank you guys sooo much! yes, the gauges did the hula before they stopped working all together. I hope to get this repaired today. thanks again, I cann't tell you how much this site is helping me with my sons truck. will keep you posted with results.