Fuel gauge help

MiradaCMX80

Well-Known Member
Joined
May 24, 2020
Messages
61
Reaction score
12
Location
Michigan
My 80 Mirada has a new gas tank and sender unit. But the fuel gauge doesnt work. I just took the tank out of the car, and saw a wire hanging. The sender harness has a green wire which was the wire dangling, a blue wire to the sender post, and a grey wire hooked to the spade terminal of the sender (I assume ground.) What is the green wire for, and is this my problem? I've only seen the fuel gauge move once since I got the car. Can't seem to find any wiring diagrams to confirm routing and to test the gauge itself.
 

Aspen500

Well-Known Member
Joined
Feb 14, 2015
Messages
7,279
Reaction score
2,933
Location
Rib Mountain, WI
You should have 5 volts on the blue wire at the post and gray is ground, eventually. It's splices in and shares a grounding point with a few other things and I'm not sure where the ground point is on a Mirada. If your interior and rear lights all work, the body ground point is good and the wire from the sender is broken (assuming it doesn't have continuity to ground). The sender is a variable ground. I can't remember exactly off hand right now but it's something like 10 ohms (full) and 90 ohms (empty). 12 volts goes into the gauge voltage limiter and comes out as 5, runs through the gauge and continues on to the sender. What the green wire is,,,,,,,,,,,don't know, sorry.
Check the voltage at the blue wire for approx 5 volts and check for continuity to ground on the gray. If you ground the blue wire, the gauge should peg on full.
If the power and ground at the sender are OK, it's most likely the gauge since the sender is new. New just means new, doesn't necessarily mean good but since the gauge has never worked you can assume the sender is good. About all that's left after that is to try grounding the gauge right at the cluster, which may be easier said than done, and seeing if it pegs on full or not. Do not pull the gauge and bench test with a 12 volt battery, then you WILL have a bad gauge.:D
 

SRTMirada

Well-Known Member
Joined
Dec 29, 2015
Messages
110
Reaction score
71
Location
Niagara
The original harness has three wires. The grey is the ground, the dark blue is the sender and the light blue is the low level warning.
20200531_142520.jpg
 

MiradaCMX80

Well-Known Member
Joined
May 24, 2020
Messages
61
Reaction score
12
Location
Michigan
The original harness has three wires. The grey is the ground, the dark blue is the sender and the light blue is the low level warning. View attachment 40377

Ok....obviously the sender on my car doesn't have low level. So in theory, my gauge should be working with the sender wire and ground, assuming all is well. I pulled the cluster out to replace a bunch of bulbs, and the voltage limiter. When I reconnect the cluster, I'll test as Aspen500 outlined to check the gauge. All of my rear vehicle lighting is good and working, so the ground SHOULD be ok. My other gauges (charge and temp) work too. Thanks for the input, guys!!
 
Back
Top