72 Blazer 4WD fuel gauge problem

[Moreyel]

I'm new to posting and trying to get involved in some of the great discussions on this really fine website. So please ignore my ignorance......I'll figure it out!

I posed this thread in the 72 Pickup forum and couldn't figure out how to move it here.

I've been reading many threads on fixing my gauge, but haven't been able to figure this one out.

My gauge only registers empty to 1/4 full. My new sender reads 0 ohms empty and close to 90 in the full position. I followed the tan wire to the fuse box, finding no problems there.

I disconnected that wire at the fuse box and the gauge goes just past full to about 1-2:00. Not to the 3:00 position forums said it should go to.

When I ground the fuse box terminal, the gauge goes to MT.

With the sender in the MT position, it reads correctly. When I raise the float to the full position, it won't go past 1/4 full.

Any help will be greatly appreciated.

[Chulisohombre]

There should be another ground wire from the sending unit to the frame. If its not there or corroded it won't put a good signal to the gauge. Mine was off completely and putting it back on my gauge worked perfect. Check that. Otherwise your junction block may be dirty or loose and not Making a good connection. There is two more connections iirc under the dash that could be loose before the harness to the gauge cluster. That or your printed circuit could be not making a good connection. Do you dash light work correct. I had to add a better ground wire direct to the gauge cluster to get the lights and turn signal indicators working correct.

[Moreyel]

Great suggestions Hombre. The new sending unit does have a separate ground (where the stock one didn't). I did run it straight to ground, but I will follow your advice and check the others. When you say junction block, do you mean where the wires meet at the fuse box connection? All I've found so far, is the tan wire from the sending unit straight up to the fuse box, then I assume it goes to the cluster from there. Poor grounding does make sense though.

[Chulisohombre]

Yeah that's what I meant. For some reason I was thinking junction block because the tan wire from the brakes master goes Through there. But also the fuse block has all the other wires going through from the firewall too. It comes from there through the dash harness and up through the harness with the steering column and start switch wiring and splits in between to the gauge cluster. I believe there is two connections I between those that can come loose. Been a couple years since I've been under my dash. Just unplugging all the connections and reconnecting them can Make them have good Connection again if They area lil loose. Also check the harness that plugs In the back of the gauges. If you pull the cluster check the grounds from the printed Circuit as well. Make sure Nothing Is Shorted Or Burnt. Mine was cut from previous owner who hacked It To Put in a tach.

[Moreyel]

I'll work on it Sunday. Look for my response back to you that eve.

I didnt know they made a 3/4 ton Blazer in 72.

[Chulisohombre]

They didn't make one any year. I built mine 3/4 ton for strength. I kept breaking my half Ton stuff.

[swyfor5]

Sounds like a ground issue to me. But I had to go 1 ton!

[Chulisohombre]

I'd like to go one ton. But 60s aren't raining from the sky lately. Lol. Seriously. I'm only going 35s but I've broken two rears and two front hubs. Now 3-4 ton with the bigger outer bearing so is a little stronger plus the bigger wheel studs which i was also Breaking on the stock stuff. Also 4 wheel disk for better braking.

[Moreyel]

Swyfor5, with the other tests I showed, where the gauge reacted like it did, I had discounted ground. I'm hoping I was wrong.

[Moreyel]

Swyfor5: tell me about your brown Blazer. How much lift? What size tires/wheels. I'm just finishing a crate engine install and I'll be needing new rubber. What would I have to go through to make it look similar to your or even a little less?

While it's been on the lift, I had the springs re-arched and put all new suspension bushings in. I'm not afraid to take it few steps further!

[DANTES JIMMY]

I can almost promise you that yo have a ground to the printed circut or to the gauge or to the entire cluster that is corroded or bad

[Truckman73]

My issue was the little white flat resistor on the rear of the gauge went bad. $12 fix

[Moreyel]

Truck man, how did you test the resistor? Or was it just noticeably bad?

Dante's, Thanks. I'm pulling the dash cluster Sunday. I'll let u know what I find.

Thanks to everyone. What a great website! I hope I'll be able to help someone in the near future.

[Truckman73]

http://67-72chevytrucks.com/vboard/s....php?p=5410890

Ran throughout the bench test

Originally posted by hatzie on 7/1/12

The problem you're describing is usually a damaged or loose calibration resistor. You'll find the resistor (usually white with a brightly colored center that corresponds to the resistance value) on the back of the gauge can between 2 of the three studs. Time, vibration, and moisture in the air can corrode and/or wear through the thin metal contact surface of the resistor.

When the resistor makes proper contact the needle will sweep to the full range of the gauge. When the resistance changes, from loosing contact, the needle will no longer move to the top of the gauge but bottom is unchanged. When you change the gauge out it works again because the new gauge has a fully working resistor not because the gauge itself was bad. It's possible to fix the resistor by lightly buffing the contact with fine steel wool (for corrosion) or adding washers that are slightly larger than the bottom of the retaining nuts to get by the vibration damaged contact surface.

I'm a cheapskate, I try to go after the cheapest part first

[Moreyel]

Well, I sincerely thank all of you that posted help advice. I took out the dash and found the fuel gauge resistor loose. I cleaned the terminals, added flat washers and got it snugged in. BUT, that wasn't the problem. Those that said it was a bad ground were right! I ran a new ground from the sending to the frame, and voila, that fixed it!

I took the opportunity to do a solder repair on the circuit board and sent for LED's to put in.

Has anyone purchased repair panels they are happy with? From who?

I thank you all again. I can't get over what a great website this is!

Morey

[Chulisohombre]

Figured that's what it was. I got my repair panels from brothers trucks. Fit good and went in place pretty well with no real trimming.