I have a 69 Coronet R/T with a non rallye dash. All gauges/dummy lights were previously working. ran the car for the first time in about 6 months yesterday. all worked well (fuel gauge was reading about 3/4 full and temp gauge increased from C to middle of range over the first 5-10 minutes as normal). then out of the corner of my eye I saw the temp gauge peg out on Hot rapidly and then several seconds later went all the way back below Cold. quickly afterwards the fuel gauge went above full and stayed there until shut off. following morning started car up and neither the temp gauge nor the fuel gauge moved.

I don't want to mess anything up, but need help proceeding.

What order should i do things? really don't want to pull the cluster...
from reading I would guess it is the voltage regulator on the cluster?
Isn't there a way to ground the terminal at the temp sender wire end to see if the regulator is good or bad?

any help would be appreciated.

Thanks

actually it sounds like you ate the gauges.
the vr went full 12 volts and pegged your gauges till they died.

but yes, at the temp sending unit under the hood, you can hook up a test light.
turn the car to on/run.
if it blinks your vr is probably still working.

shut it off, then ground the wire and turn the car on. if the gauge moves to full, then both the vr and the gauge still work fine.

but I am betting the light doesn't blink and is on full time, and the gauge doesn't move.

Check out this link which explains how your gauges work:
http://www.allpar.com/history/mopar/electrical2.html

I'll add this, for checking the accuracy of the gauges.......after you fix your problem which is likely the voltage limiter as previously mentioned.
http://www.dodgecharger.com/forum/index.php?topic=1971.0

Just so I know I do/get this right...

1) If I pull the wire connector on the temp sender at the water pump I can use a test light or VOM to test whether or not the voltage regulator in the dash is working. To do this I clip on to the stud at the sender and put the other end of the light or VOM in contact with the connector on the engine harness (i.e., just put the light or VOM in series with the normal wiring)? With the key in the ON position, but the engine not running, the light should blink or the voltage should oscillate from 0 to ~5 V. This would mean the voltage regulator in the dash cluster is working. If the light stays on or volts don't switch on and off then the regulator is shot.

2) To test if the temp gauge in the dash is toast I start the engine and briefly ground the wire that connects to the temp sender to the block... if the needle on the gauge rises up towards hot I stop the test knowing that the gauge is still functioning?

3) if the light doesn't blink (constant on) in test 1 and the gauge doesn't move in test 2 it likely means that the voltage regulator in the cluster crapped out then my gauge became exposed to more than 5 volts (12 volts) and it fried? IF the light stays on, but the gauge appears to work i got lucky and just need to replace the voltage regulator in the instrument cluster?


Sorry for drawing this out, but I just don't want to make a dumb mistake and cause more damage to anything.

Thanks

test 1.
key on, engine off.
test light grounded and touching the wire going to the temp sending unit.
blinks if working. if solid on or no blink, the vr is dead.

vom will read average of 5 volts, or 0 to 12 volts switching. depending on your vom.

test 2. only needed if the test above passed for a good vr.
engine off, key off, wire the temp sending wire to ground somewhere. doesn't matter to what as long as it is grounded.
turn the key on, engine off. gauge should move to full.
when it gets about half way shut off the key.

if the light stays on, do not try grounding the sending unit wire. if you didn't fry the gauge, you will.

the vr works by turning 12 volts on and off to average 5 volts.
constant light means it is supplying a full 12 volts.
blinking means it is giving 5v.

typically they break by giving no light and no power. but a few get stuck full on.

So a test light at the water temp sender wire end in the engine bay does not illuminate or blink with keyed power. So is the VR in the cluster bad for certain? Since this circuit is broke I can't test the temp gauge except by going directly to the 2 posts on the back of it and powering it with a few alkaline batteries in series as I read about correct?

My car is a 69 Coronet R/T w/ non-rallye dash and of course in this case to make things tougher it has A/C.

Can the VR be changed under dash and can I get to the posts on the fuel and temp gauge from underneath? At this point the gauges could still be good and the VR may be able to be changed in place... So I'd like to try that first if possible. Any tricks to doing this in place? I guess also confirming the gauges work is a priority as if they don't then the cluster needs to come out anyway and the VR would be changed then. The thought of puling the cluster makes me sick so I want to make sure I only do it if necessary and avoid it if at all possible...

Thanks in advance

if it worked before, then it is dead now.
you can double check at the fuel sending wire as well.
if they don't blink the vr is dead.
you are correct, no way to check the gauge without an external source of power.

you could jump the gap in the cluster, but not sure how you would do it without it being out.
2 AA batteries in series will push the gauge half way.

if you look up pictures of it, you can see it is a 3 prong silver box.
the only catch is there is a capacitor that has a wire that goes into one of the slots.

you could probably reach up and pull it out, but making sure that wire is there, might not be possible.

as for the gauges, you probably can get to one of the lower gaugues. 2 alligator clips and you should be able to test it.
the posts should be exposed. you will just need some long lengths of wire to pull it off.

What's the easiest way to get to the instrument voltage regulator on this dash? under the dash, through the radio hole, etc...?

based on this it is all the way on the left, just above the fuel gauge.

I just dug up this picture. guess the regulator is above the fuel gauge to the left of the steering column.... so only way to access without pulling the cluster entirely would be from underneath... hopefully this can be done without dropping the column if the gauges appear to be OK?

see the canister to the left.
there is a black wire that goes to the center prong on the vr.

just make sure you get that back in when you plug in the new one.

if you can reach up past everything, you should be able to do it without removing stuff.

I would unhook the battery. just incase so you dont bridge the amp meter connections right next to it.

turns out the dash voltage regulator (VR) is from RT-Eng

so i did further testing that may or may not help:
when I turn the key on the LED on the VR does light up (solid).
a testlight at the water temp sensor end of the violet wire in engine bay still does not light with the key on
i have continuity from the temp sensor end of wire to the bulkhead connector
when i put a 3 V batter across the fuel gauge it does not move... i can't easily get to the back of the temp gauge

what do you think is going on? doesn't the LED on the RT-Eng VR mean it is functioning?

seeing it is an rt-eng regulator i am puzzled? both gauges failed in the same short period of time, and that VR has protections in it...
how/why would both gauges fry w/ the rt-enf VR in place?

I built my own, so I don't know what is in that one. can't say what the light means other than it has power.

no light at the temp gauge blinking or otherwise says nothing is making it out.

did you try the batteries wired in both directions on the fuel gauge? if you aren't sure which is the ground, you could have wired it backwards and it didn't move because of that.
picture shows the outer one is ground though.

the vr has 3 prongs. pos, neg and output.
pull it out and wire it to the car battery directly. see if you get 5 volts out or at least a test light lit.

that way you will know for sure if it is wiring or the vr.

Your Rt-Eng limiter is bad according to their website............
Says it should blink: http://rt-eng.com/rte/index.php/RTE_limiter

I have been installing his limiters and tach boards, I have not had or read of issues with his stuff. Anyone else have issues?
I still think you should use a solid state replacement.

I appear to be getting full voltage out of the output post... assume that means it failed and then cooked my gauges...

Anyone know how to get a hold of the folks at RT-Eng? can't find contact info on their website...

I thought a big advantage of the RT-Eng limiter was to protect the gauges from these types of events?

I assume the cluster needs to come out and the gauges repaired/replaced and the VR replaced?

did you recheck the gauge? swap pos and neg on the posts just in case.

just to make sure before pulling anything.

and it is curious to me why you don't get a light at the sending unit if it is giving 12 volts out.

Sorry... I did reverse the poles on the 3V source when checking the fuel gauge... couldn't get it to work no matter what I did.

If the gauge burned wouldn't this break continuity to the water temp sending wire and be why i don't see voltage there?

I'm puzzled also, but i don't know much about this stuff???

It can't be the cluster grounds can it? the lights in the cluster consistently are working fine... as to is oil pressure dummy light..