clewi23

Hello! I am new to the forum and about to get me restored 65 Mustang 289 back on the road. However, I cannot get the Fuel and Temp gauges to operate correctly. I have done the IVR test - pulse at end of sensor line. I get the gauges to move when grounding, (with sensor connected), and everything else works fine. I have analyzed the back of the instrument cluster and cleaned all connections. Wiring and fuses seem fine. Both sending units were replaced new. Just replaced temp sending unit again and no change. I don't know what else to check? Any ideas from you experts out there? Thank you!

gjz30075

Do the gauges move to the extreme end when grounded? When they're 'not working', are the needles moving at all?

clewi23

Hello and thank you for the replies! I have now installed a new temp sending unit and have checked all grounds in engine compartment. Everything seems okay. I have pulled the instrument cluster to double check frayed wires, and make sure all is connected correctly. NOW the IVR seems to be operating incorrectly. When I connect the temp gauge to it correctly the gauge pegs at HOT. I do not have a voltage meter (probably need to buy one of those), but when I touch a simple volt/lamp connector - clip to IGN (input) side and touch outgoing - no pulse and the gauge rocks to HOT. Do I need a new IVR?
Both gauges peg to FULL or HOT when grounded at end. Had pulse last time I wrote, now just full light, no pulse. Thank you!

clewi23

also - the instrument lights and turn signals work on my 65 Mustang. I do have the instrument cluster out right now as a few of the lenses needed work. A good time to change out IVR IF that is the problem. One other note of interest. After driving it recently (before removing the instrument panel), the alternator seemed to be trying to turn AFTER I had turned off the engine! Sounds like something is not grounded? I am stumped...

bop11

Alternator problem is in the regulator. There is a cutout relay that keeps this from happening. Either it is wired incorrectly or the contacts are welded together.

clewi23

Thank you! You mean the Instrument Voltage Regulator on the back of the cluster? I also found that the regulator under the hood had not been grounded until I found that loose wire a while back. Is that regulator okay you think? I sure appreciate the feedback?

bop11

For alternator, I mean the regulator under the hood in the engine compartment.
The gauges, temp, Oil pressure, gas gauge and others, if you have them, have one side tied to the constant voltage regulator. The power to the regulator connects through a plug to the Accessory terminal on the key switch. The other terminal on each gauge goes to its corresponding sensor. If one of the sensor lines is shorted to the chassis,it will make the corresponding gauge go to full or high. If the wire is broken, the gauge will read nothing. So if some gauges are working then the Constant voltage regulator is probably OK.

clewi23

Thank you Bop11! I sure appreciate your input. So the Voltage regulator under the hood having not been grounded all this time has probably fried it ? The gauges do work when applying a ground to the wire. The gauge worked when the IVR was attached correctly, but both went to FULL and HOT respectively. I am going to double check the alternator and make sure it is wired correctly - I thought it was - and all other grounded lines. The wiring is pretty much brand new as I replaced with compete looms in most cases. Do you think I need to replace both regulators and is it true that the IVRs from Mustang supply houses rarely work? Not sure what next step is. Thank you so much for taking the time to help me with my classic!

bop11

The output of the constant voltage regulator should be about 5-6 volts. The original regulator was a bi-metal strip that bent when current flowed through a wire wrapped around it similar to a turn signal flasher but much faster. The average voltage at the output was fed to the gauge. If the CVR is stuck or bad in that the contacts are always closed , then the gauges will always have about twice the voltage they should and will go to the totally high. Get a cheap meter and check between the temp sender wire and ground, If it is above 6 volts the regulator is bad. IF not continue.
You said you replaced the temp sender. Take the wire off the sender and attache it to the old one. With the sender in your hand, not touching the car or engine, turn on the ignition. Does the temp gauge go all the way up? If yes pull the wire off the sender and check again. IF the gauge goes all the way up you have a ground problem in the wire or the gauge. Pull the wire off the back of the gauge. Is the gauge still pinned? If so bad gauge. Similarly check the other gauges that don't operate. The gauges are volt meters that measure the voltage between 12volts and the connection to the sender. The higher the temperature the lower the resistance of the sender and therefore the more voltage between 12Volts at the positive side of the gauge (the one connected to the constant voltage device not the one that goes to the sender) and the top of the sender unit.
Pull the cover off the alternator regulator and check that the contacts are not welded together (free to move) Do NOT bend the contacts as this is how the voltage control is set. These contacts vibrate very fast and just like the instrument voltage control, they average the voltage to the battery. Look at the coils to see if these show signs of being burnt or look brown from heat. If all looks good yo probably don't need a new one. However they are cheap about $35 at Mustang Barn, so it might be worth while just to replace it if you haven't already. A solid state constant voltage unit is only $18.

clewi23

Thank you again Bop11! I will do as you suggest. I did see that the wiring appears to be messed up at the alternator regulator. I just plugged in the loom I bought - appears to be in the wrong places. I am now trying to be sure to connect the correct colors to the tabs on the regulator. I have a wiring diagram, but hard to tell where they go in every case. I "think" I have it figure it out. Just looking for a good diagram that tells me which color wire goes to the 4 letters on the regulator. I can't remember them now, but I know it starts with green/black on I, etc., Thanks again for all your help. I will keep you posted!