75 Dart fuel temp guages inop HELP!

[Matt70]

I know it's not an E body but could use some advice.
75 Dart Sport /6
Back ground- Fuel and temp guages inop. Figured it was the voltage limiter so replaced it. No luck Added ground wire to intrument cluster no luck. Then I noticed I keep blowing #6 3 amp fuse. My understanding is that it protects the instrument cluster lights and that circuit feeds the limiter.

There is some corrosion on the headlamp switch. Other than that I can see anything physically wrong.

Should I have voltage on both terminals of the amp meter? I think I read somewhere I should not???

Any help would be greatly appreciated,    Matt

[dodj]

You should have full voltage at either terminal. You should get zero voltage when you have your meter leads across the ammeter terminals. If I read your post correctly, you did not realize the fuse was blown before you changed the limiter, or did you begin blowing it after the limiter change?

[Matt70]

I think it was blown prior to the limiter change. Thanks for clearing up the amp meter question. Does all the cluster power come through the headlamp switch? Thanks for the help,  Matt

[Matt70]

Been reviewing the diagrams (confusing) Seems like all the lights and guages power comes in from the #1 pin (12 O'clock) on the cluster main connector. Anyone know for sure? Thanks,  Matt

[dodj]

Does all the cluster power come through the headlamp switch?

I'm not familiar with the Dart/Duster dash but it appears that your h-light sw has a dimmer in it so the dash lights power would go through the h-light switch assembly. Power for the gauges/limiter, probably not. I don't have a diagram for a 75 Dart, so I can't be any more specific. If the dimmers for your Dart are similar to the e-body dimmers (looks like a similar design),  they are problematic.

[Matt70]

OK, tested power to pin #1(12v in to cluster) disconnected from cluster got 12V. Plugged back into cluster turned key on fuse blew. Removed connector and retested no voltage. So problem is in cluster.

Replaced fuse and disconnected head lamp switch, turned on key fuse blew. So problem is not headlamp switch.

Checked resistance on fuel guage 15 ohms. Did D cell test on gas guage and it did not move. So gas guage is bad.

Checked resistance on temp guage infinite. So temp guage is bad also.

My guess is one of these guages has an internal short causing the fuse to blow. Does this sound correct?

[dodj]

If you are measuring across the gauge terminals, 15 ohms for the fuel gauge seems ok to me. Checked a spare cluster (Challenger) and got 15.2 ohms. Infinite for the temp would not be good. But to find where the short is you should be checking resistance from the limiter connection to cluster case ground - it should be infinite.
You should also remove all the cluster light bulbs just to remove any possibility of a short in a light socket.

[Matt70]

Thanks Dodj, I'll do that. Even if I have 15 ohms on the fuel gauge when I applied 3 volts the needle didn't move so it's bad also. I'll keep testing tomorrow afternoon. I really appreciate the advice.                Matt

[Matt70]

I checked the resistance between the limiter connector to the cluster housing, on one prong inlet I got .002 ohms so nothing really I assume?

Pulled all sockets and still blew fuse

Pulled both temp and fuel gauges incase they may have an internal short, still blew fuse   

Kinda lost on where to go next. Maybe the circuit board has a short? 

Any ideas would be appreciated,  Thanks   Matt

oh and anybody know where to buy replacement gauges or entire clusters? 

[dodj]

I checked the resistance between the limiter connector to the cluster housing, on one prong inlet I got .002 ohms so nothing really I assume?
 

That's your short blowing the fuse.

[Matt70]

So it's in the circuit board! Awesome!   

Any ideas on where to get a new one and replacement gauges?

Thanks for all the help,   Matt

[ShelbyDogg]

So it's in the circuit board! Awesome!   

Any ideas on where to get a new one and replacement gauges?

Thanks for all the help,   Matt

Matt,

You've got the whole circuit board right there in front of you. Use your meter with the continuity "beep" mode and follow the traces with the probes till you find out where the short is. If you pull the board off, that could help too. There is something in there that is shorting something to ground. You just have to find it.  I've cut traces with a razor blade to isolate sides then bridged "the gap" with solder to reconnect it.

Good Luck!

[Matt70]

Rob, thanks for the advice really appreciated. I'll give that a try. Take it easy.   Matt

[ShelbyDogg]

Also check that capacitor on the bottom. disconnect it and see if fuses blow.  It shouldn't pass any voltage to turn a test light on. You do have a test light right? That is a filter capacitor that smooths out the voltage going into the regulstor.

To check guages, use the regulstor output, (5volts pulsing?) with a 10 ohm resistor in series with the ground side of the tested guage. the needle should go to "F" or "H" and not go higher or lower.
The regulator is simple. The case gets grounded, the terminal in gets 12v, and the output goes to the guages.  I use a small 12v battery from my hand held spotlight, to power stuff up for bench testing and a couple of alligator clip ended test wires.

[Matt70]

Thanks for the info ShelbyDogg, I did leave the capacitor unplugged to see if the fuse blew, it did. I used D cells to test the gauges. Right now I'm looking for a cluster to put in. Found a couple on ebay but my daughters car Sh#t the bed last weekend so the extra cash went there. Broke down on the way to opening night Pueblo Drag races!    Hope to get one next week.  Thanks,  Matt