• When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.

Instruments going to far right side - 66 Sat??

AR67GTX

FBBO Gold Member
FBBO Gold Member
Local time
1:29 PM
Joined
Jan 28, 2012
Messages
4,806
Reaction score
4,318
Location
Arkansas
My 66 is having some sort of instrument electrical issue that is sidelining it. After starting the engine and letting it run a few minutes the temp and fuel gage start slowly heading to the far right side of the gages and pegging there. The alternator seems to read high too although it's not going all the way over. If I shut the engine down and let it set for a few minutes, when I re-start it the gages read OK again and continue to do so for a minute or two, and then they start the steady progression all the way right as far as they can go.

My first thought was a sticking instrument voltage regulator so I bought a Standard replacement and plugged it in only to have it continue doing exactly the same thing. I've noticed that when the temp and gas gage start going over and I rev the motor up, while the alternator gage goes over quite a ways on the charging side, it will then start a frantic back and forth movement over there until I let it idle back down.

So - I've about exhausted the extent of my electrical know how at this point. Could it be just a bad voltage regulator under the hood that is overpowering the instrument regulator?

I haven't tried to take any system voltage checks yet - one of those things you only think of after putting the car up. Any thoughts or help is appreciated.
 
It could be the contacts in the voltage regulator sticking.
Pull the cover and check for proper mechanical operation.
If all looks good there, the pull the center connector in the bulkhead.
Look for melted wires/housing.
Clean the connector contacts with a small brass bristle brush.
Coat the male contacts with dielectric grease.
Plug it back in and see what it looks like then.
 
Last edited:
Well the voltage to those 2 guages are constant, the only varying input is the ground which are separate ( temp sensor and fuel level sending unit ) ....need to 1st verify you have 5 volts to both gauges then check your grounds. Full ground = pegged gauges.
 
Ok - not sure if it’s points type or solid state since I’ve only had the car a couple of months but I’ll pull it tomorrow and have a look at it. I think the car had been sitting up for several years before I bought it so if the VR could cause that type of instrument behavior, hopefully that will resolve it.

thanks
 
Well the voltage to those 2 guages are constant, the only varying input is the ground which are separate ( temp sensor and fuel level sending unit ) ....need to 1st verify you have 5 volts to both gauges then check your grounds. Full ground = pegged gauges.

I wondered about the ground. The cluster has the metal plate at the top that the screws securing the cluster in the dash run through. Right now I have the dash pulled out slightly so none of the screws are in place if that plate and the screws provide a ground path. But it’s behaving exactly as it did before I pulled the dash screws. So is the grounding of the cluster through the harness or is there a supplemental ground to the dash frame somewhere?

Not sure of easiest way to check voltage at the gages with the cluster mounted in the car.
 
The cluster grounds to the dash frame via the screws.....at least my 66 Belvedere does. Everything went berzerk after replacing the dash lights and I just set it in place without the screws to check the bulbs.
 
First thing is to verify the charging rate. Get a volt meter on the battery and watch what it does as you rev it up. 13.8 to 14.2 is a target range, The charging system and ammeter are totally separate from the other gauges. I would verify that first. Period.
 
I wondered about the ground. The cluster has the metal plate at the top that the screws securing the cluster in the dash run through. Right now I have the dash pulled out slightly so none of the screws are in place if that plate and the screws provide a ground path. But it’s behaving exactly as it did before I pulled the dash screws. So is the grounding of the cluster through the harness or is there a supplemental ground to the dash frame somewhere?

Not sure of easiest way to check voltage at the gages with the cluster mounted in the car.
I was referring to the grounds for those 2 gauges in question, they do not ground through the dash frame. They ground at the temp sensor and fuel level sending unit. Now if your voltage limiter is bad and is supplying full battery voltage to those gauges it will cause them to peg and eventually burn up...plug the cluster back in and turn the ignition on, verify battery voltage into the limiter and 5V out...very easy to check, sometimes requires laying on your back looking up at the cluster!
 
I've noticed that when the temp and gas gage start going over and I rev the motor up, while the alternator gage goes over quite a ways on the charging side, it will then start a frantic back and forth movement over there until I let it idle back down.

Do not ignore the obvious. If the input voltage to the voltage limiter is excessive the gauges will respond the same way. Head to the right. A limiter drops the input voltage to approximately 5 volts. If the input voltage is higher then the limiter output to the gauges will be higher. Like I said get a voltmeter on the battery and see what it says.
 
Thanks all - I will try to run some voltage checks and see what is going on. I have a spare 67 cluster sitting on my work bench so I’ll figure out where to go with my meter probe from it.
 
Pretty sure the old style voltage limiter doesn't put out 5 volts it's a time averaged thing where it turns on and off periodically and the gauges have a bunch of dampening in them to smooth out the square wave.
I've never put a meter on that part of the circuit but I don't think it would read 5 volts.
 
Had one sticking and could hear a ping when contacts separated. Wth is that? Then saw gauges going up, ping gauges going down.
 
I've noticed that when the temp and gas gage start going over and I rev the motor up, while the alternator gage goes over quite a ways on the charging side, it will then start a frantic back and forth movement over there until I let it idle back down.

Do not ignore the obvious. If the input voltage to the voltage limiter is excessive the gauges will respond the same way. Head to the right. A limiter drops the input voltage to approximately 5 volts. If the input voltage is higher then the limiter output to the gauges will be higher. Like I said get a voltmeter on the battery and see what it says.
I get what you're saying but how much voltage to you think it takes to full sweep those guages? And that's assuming his sending units are at their lowest resistance reading...I've had my car charging at 19V one time and it never pegged the guages...not saying it isn't possible, just seems unlikely to me......however it is probably the easiest thing to check, alternator output...
 
Had one sticking and could hear a ping when contacts separated. Wth is that? Then saw gauges going up, ping gauges going down.

Unfortunately my hearing is probably not good enough anymore to hear it. But it would be a real coincidence that two instrument voltage regulators would be identically bad and exhibit the exact same behavior. I was suspecting the alternator regulator but was seeking some concurrence that could cause this behavior. I should be able to check it tomorrow some more.
 
Unfortunately my hearing is probably not good enough anymore to hear it. But it would be a real coincidence that two instrument voltage regulators would be identically bad and exhibit the exact same behavior. I was suspecting the alternator regulator but was seeking some concurrence that could cause this behavior. I should be able to check it tomorrow some more.
I agree, very unlikely
 
Just unplug the regulator and see what happens. You can run for a while with no alternator.
 
Pulled the voltage regulator and pulled the cover off - it is a points type of some USA manufacturer. I ran a points file across the contacts and put the cover back on - the innards are too different from the details of the original in the FSM to do any trouble shooting as it describes. It doesn't appear to have an adjustment to tune the voltage output. I'll give it a try after lunch and see if that makes any difference and measure the voltage. If still acting the same I may just swap the one off my 67 GTX over to it temporarily and see what that does.

I'm no electrical genius but sort of doubting its a ground problem. As noted above the gages going all the way over to the right side indicates a full ground condition from the two senders - so those two gages are apparently isolated from the cluster ground path.
 
Auto Transport Service
Back
Top