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Opeler
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161 Posts
Discussion Starter #1
Short story long. Haven't had instrument lights in a while and have tried to fix it with no luck in the past. Finally got around to pulling the intrument panel again to track down the issue and found that the last light in the series wasn't grounded right and now have dash light again but the fuel/temp gage has stopped working now. In troubleshooting this I've hooked a small external battery to the gage to see if the gage worked. It does. But doesn't have power from the wiring harness. If I understand the system right, the power wire goes to the fuel gage and has a jumper wire that goes to the temp gage. Fuel gage 2 wires. Temp gage 3 wires, one of which is the jumper from the fuel gage so I assume this is the power wire since it goes to both gages. Temp gage other 2 wires read the resistance from the temp sensor. Fuel gage other wire hooked to fuel tank level sensor for ground resistance to operate gage. That is how I understand the system. Now, where does the power come from for the power wire? I've checked the fuses, even changed a couple out just to be sure. Still no power. Since the fuel and temp is in the same pod and powered by the same wire I assume that if the fuel gage doesn't work then the temp gage won't work either. Which is why I'm hesitant to start the car to get a temp reading. Any ideas? Gage worked before I pulled the panel and fixed the lights.
 

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Resident Curmudgeon
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1,405 Posts
If we're talking about a GT, my wiring diagram shows that power comes to the fuel gauge via a black/red wire from the oil pressure gauge.
 

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2,497 Posts
Ok, the red/blk wire goes to the oil + feed on the back of the gauge then goes to the 6 way union that is mounted between the speedo & tach, off of that, power to the tach, & lower right of the directional indicator. Then goes to the fuse box, #2 from the left, 5 amp fuse. If you have power to the tach, & oil gauge, look for a broken wire, since they are all feed power from the same source. :yup:
 

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Opeler
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161 Posts
Discussion Starter #4
Ok, the oil press gauge works so must be the wire between them. I had to patch that wire once and even redid the splice thinking I might have messed it up. Well, looks like I did. I'll track it back to where it goes bad and repair/replace as necessary. Will have to wait till Sunday though. 3yo grandson visited tonight keeping me away from the car and spending the day tomorrow autocrossing my Miata.

Thanks guys for pointing me in the right direction.........hopefully. Get this fixed and with dash lights working I'll be able to drive it more. Couldn't/wouldn't drive it after dusk because of the instrument lights.
 

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Opeler
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161 Posts
Discussion Starter #10
Got back on it this afternoon. I do have power to the gauge. Still doesn't work. Even took the power wire off the oil pressure gauge and put it on the fuel gauge. Again still don't work. Took a partially discharged cordless drill battery with about 3 volts and put it on the fuel gauge and it pegs the gauge. So that should mean the gauge is good. So with power to the gauge and still not working, I guess that means that the next step is to take out the spare tire, jack, small tool bag, fire extinguisher and back tray to get to the fuel tank and check out the sending unit. Right? :confused: :ugh:

On a side note, very hot out but took my class autocrossing yesterday. :D
 

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Bikini Inspector
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5,771 Posts
or you can take out couple tail lights and reach in with an 8 mm I believe.

might have to remove spare tire shelf first. mine has been out for long time.
 

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Since you have access to the back of the gauges, turn power on, then ground out the input fuel or temp wire form the sending units, if the gauges are working correctly, then they will peg to the other side. Not sure if hooking power (low v cordless batt) is a good indicator, not designed to work that way, it will cook it. Was everything working prior to the repair ??
 

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Opeler
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161 Posts
Discussion Starter #13
Just tried that. Ended up popping the fuse causing loss of all gauges. New fuse brings back everything except the fuel gauge.
 

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Got back on it this afternoon. I do have power to the gauge. Still doesn't work. Even took the power wire off the oil pressure gauge and put it on the fuel gauge. Again still don't work. Took a partially discharged cordless drill battery with about 3 volts and put it on the fuel gauge and it pegs the gauge. So that should mean the gauge is good. So with power to the gauge and still not working, I guess that means that the next step is to take out the spare tire, jack, small tool bag, fire extinguisher and back tray to get to the fuel tank and check out the sending unit. Right?
Yuck Yuck
I've used an external power pack to test the circuits before.

Mostly to bypass a fubared power window switch..I've also done this to engage the electric fuel pump.
Both legs has to be connected.
 

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I don't remember it blowing any fuses, just pegs the gauge, is the temp gauge working ? you can test the temp gauge the same way. But it shouldn't blow a fuse, look for a short to a + wire somewhere in the back of the dash, or check the hook up's
 

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Opeler
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161 Posts
Discussion Starter #16
The gauge saga continues after a week of honey-dos, 100-deg heat and babysitting grandson. Pulled the tail lights and checked the connector at the sending unit. Seemed ok. Put my multimeter reading DCV in line and applied power to the system. Got what I figure is appropriate reading for the amount of gas in the tank. Tank has about 1/4 tank of gas and read about 2.5 volts on the meter. Know I have power to the gauge but checked again anyway. Put the multimeter probes on the gauge terminals and promptly popped the car fuse. Every time I do this it pops the fuse. Could this mean the gauge is bad? With an external power source I can get the needle to peg full (gauge disconnected from the system naturally when I do this). Thinking about replacing the fuse (again) and starting it up and let it run for a while to see if the temp gauge is working. I tried the suggested jumping of the temp gauge and it also pops the fuse.

With the gauge popping fuses makes me think the gauge is bad. Now where can I find one.
 

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Opeler
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161 Posts
Discussion Starter #17
Success

This whole fiasco started when I fixed the instrument lights. Got those fixed and lost the fuel/temp gauge. I thought it gave every indication of a bad ground but just couldn't find the bad ground. Went through the system multiple times. Asked for guidance here and followed the advice and still couldn't find anything wrong but still didn't work. This morning I went through triple checking every connection, and I mean every connection. Found a loose connector at the fuse box. I know I checked that multiple times but somehow missed it. Fuel/temp gauge now works!!! And the dash lights still work!!! :veryhappy Even after I put the dash, steering column and tail lights back together. Now I can take the GT out for some exercise and celebrate. :cool:
 

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Registered
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This whole fiasco started when I fixed the instrument lights. Got those fixed and lost the fuel/temp gauge. I thought it gave every indication of a bad ground but just couldn't find the bad ground. Went through the system multiple times. Asked for guidance here and followed the advice and still couldn't find anything wrong but still didn't work. This morning I went through triple checking every connection, and I mean every connection. Found a loose connector at the fuse box. I know I checked that multiple times but somehow missed it. Fuel/temp gauge now works!!! And the dash lights still work!!! :veryhappy Even after I put the dash, steering column and tail lights back together. Now I can take the GT out for some exercise and celebrate. :cool:
Hi
I have the exact same problem after I had the dash out.
What wire was loose at the fuse box?
Hope to find some help even though it is an old thread.


Sent from my iPhone using Tapatalk
 

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Can Opeler
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3,363 Posts
Hi
I have the exact same problem after I had the dash out.
What wire was loose at the fuse box?
Hope to find some help even though it is an old thread.


Sent from my iPhone using Tapatalk
Check all the blue wires. Blue wires are sender wires. The red fuse box connector has the wires for that guage.
Power for the gauge comes from the positive of the oil pressure gauge. If your oil pressure gauge is working the problem is either the sender wires (blue) or the small red/black wire between the oil + and fuel +. The brown ground on the gauge goes to the top of the speedometer.

The needle may just be stuck give it a few moderate taps with a rubber screwdriver.
 
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