rallye gas dash gas gauge problem

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71RALLYEDART

71RALLYEDART

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I have a rallye dash from a69 barracuda that i can not get the gas gauge to work in. I havve a new circuit board,a new rte voltage limiter,a new sending unit. All the other gauges are working. I have even had all the gauges repaired. when i got the gauges back the gas gauge started to smoke, I disconnected everything right away. When i rehooked veverything it didnt smoke buteverything worked except the gas gauge. The new sending unit is grounded, and the gauges are also. Any help would be greatly appreciated.
 
was the voltage limiter inside the gauge bypassed or disabled before you put the new vl on.
 
71RALLYEDART said:
I have a rallye dash from a69 barracuda that i can not get the gas gauge to work in. I havve a new circuit board,a new rte voltage limiter,a new sending unit. All the other gauges are working. I have even had all the gauges repaired. when i got the gauges back the gas gauge started to smoke, I disconnected everything right away. When i rehooked veverything it didnt smoke buteverything worked except the gas gauge. The new sending unit is grounded, and the gauges are also. Any help would be greatly appreciated.
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You smoked the gas gauge. I bet if you take that gauge out, take the face off (very easy to do), you will find the wire inside burnt in half.
 
Yes i dissabbled the stock limiter. And i dont see any fried wires inside the gauge. But what could cause the smoking. I cant find any shorts anywhere
 
Can anybody tell what the voltages are suppossed to be at the back of the gauge on each of the 3 studs.
 
I may be wrong but I believe you should have:

12v on one (this gets reduced to 5v internally)

5v on another (directed out to the temp and oil gauges)

last is a common ground.
 
Since you've already let the smoke out... Rather than question voltages lets focus on ohms.
Each gauge should show 20 ohms resistance beteween its low voltage post and its sender post.
Hope this helps
 
71RALLYEDART said:
I have 32.5 ohms at those two posts. What do you think that means.
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32.5 is wrong. fatory spec and allowable tolerence 20.0 +/- .5.
Outside of that will equal a gauge that can't be calibrated .
First put the leads together and zero the ohm meter. Eventually it will show the resistance within its leads. In other words, If there is 12.5 ohms resistance in your ohm meter the 32.5 ohm reading would be correct.
 
I would call whoever rebuilt the guages . The resistance doesn't make sense. As far as smoke it could be just residue cooking off the new windings. The old mechanical voltage regulators for the alt would do this.
 
I definately have smoke from a short or voltage going to the wrong place. Is the sender pingetting power from the gauge or from thewiring harness,and how many volts. The gauge is shot and i want to find out what burned it out. I spoke to the guy who rebuilt it and he said he bench tested it and it worked fine.
 
low voltage from a limiter or regulator goes into each of 3 gauges. the voltage passes through a special ni-chrome resistance wire and comes out on the other side of the gauge. The sender supplies a variable ground path on that side. The current passing through the gauge heats the ni-chrome which in turn heats the bi-metal strip its wound around . yada yada the needle moves. Too much current = too much heat = smoke.

The insulation on the nichrome wire is a blend of fiberglass and silk. it should be a pale yellowish color. It will burn to black and crumble though. Nothing is fire proof.
 
It seem like the old voltage limiter is getting hot. I watch it bend and smoke when i turn the key on. Do anybody have an idea what I should test next. This is really becoming frustrating.
 
this may be unrelated, but I will post anyways. I had an bad alternator, visually it looked fine. when we hooked everything up the fusible link in the engine bay fried immediately!! Didnt know what caused it...67dart273 told me how to chk the alt and it turned out bad. Redfish knows his chit too, so you wont go wrong with what he has to offer. I actually spoke to 67dart273 on the phone and that helps huge! maybe send redfish a pm with his # so you can walk thru it over the phone?? Then post your findings here.

Good luck!
 
For those who thought they would watch this thread to learn something, here's something...
The resistance wire in the gauge is a special nickle chromium. Its resistance per inch dictates the length required to get the proper total resistance.
Most importantly solder will not stick to ni-chrome. You might get the 2 ends captured in a ball of solder and get continuity but the resistance would be wrong.
Unless you've managed to tie the 2 ends together the wire would pull right out of the solder. Bottom line, Once burned in two or broken, it must be replaced.
 
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