Question about gas gauge resistor

[69Z28]

Hello everybody. I have had this nagging question for awhile and I hope someone here can answer this for me. First a little history...

The console fuel gauge on my 69 Z only registers to just over a 1/4 tank even when it is full. When the fuel level gets to that point driving the car the gauge starts working again. I know I may have a problem possibly with the sending unit and have gone thru all the test that have been recommended on CRG and TC. I've had the sending unit out of the tank testing and in the tank testing. When I test the gauge and the sending unit together out of the tank it works fine, but when I put everything back together it performs as it always has...just over 1/4 tank and stops. When I drive the car, making turns and all that and I know I'm getting close to that mark on the gauge the low fuel light comes on and I know the gauge is working. I can't tell you how many times I have pulled all this stuff out to fix this issue. Electrical has never been my strong suit but I am not a 'TOTAL' idiot.

The nagging question I have is the use of or not use of the resister. If the resister is installed the gas gauge gives me a totally different action then if it isn't installed. I fooled around with this all last summer with no clarifications on whether I needed this resister or not. Were there different gauge manufacturers, or is the resister for the standard fuel gauges on the 67-68-69's or for the gauge package for the 68 only console? I have 2 original console gauges, neither one has a resister on the back of it and I'm not sure why I even bought it.

Anybody have any thoughts on this? I'm still trying to fix this issue and currently in the market for a new fuel sending unit. Are NAPA's any good?

Thanks guys.

[Mark]

You need the resistor on all original GM gauges, it is what provides the downscale function of the gauge, without it the gauge will go full and never come down off the F peg.  It should measure 46 ohms, sounds like you might have a 29 ohm or so resistor back there.  Some of the reproduction gauges have it built into the windings of the gauge and its not necessary.  Don't know how to tell which repro ones have it and which ones don't.

[69Z28]

Hi Mark. Both gauges are GM originals as far as I know. One is in the console and one isn't, anyway to make sure, I can check the one that's out? Is there a breakdown, schematic drawing, picture or something I can compare how these are put together? The problem I have is when I install the resister it goes to full now that you say that. I've been really curious about it. I was told several times the resister should be there, but like I said when I install it the needle goes to full and stays there. How do I check the resister? Just touch the OHM meter + - leads to the mount holes and see what it reads correct?

Thanks. I really don't want to fool with this again this year. What about the sending unit? Maybe bad?

[69Z28]

ok. I checked the loose gauge with the ohm meter and it reads 43.0 I also checked the resistor I bought and it reads 90.0.

On the loose gauge at the bottom of the face it has AC MADE IN USA 6431022. I can't check the other gauge, it's in the console at the moment.

[Mark]

The 90 ohm resistor is for the Temperature gauge.

[69Z28]

OK thanks Mark. I know what happened then. Although it's been a few years back I ordered the resistor from Rick's and they must have given me the temp resistor instead of the fuel resistor. Things happen I suppose. Oh well, at least I can put that to bed now.

[Mark]

A 90 ohm resistor on the fuel gauge would make it read beyond full  until it got down to about 1/2 a tank, and then slowly come down to 1/2 at empty.  Thats not what yours is doing.