Gas Gauge and Tach don't work

chope97

Active Member
Messages
193
Reaction score
56
Location
Silver Spring, MD
My 71 with a 3.3 and 5speed converted from and automatic. Neither the gas gauge or tach work. The temp gauge works fine. I swapped in my spare instrument cluster and nothing changed. I checked the wires at the coil, everything looks good. I have heard about adding an additional ground to the wires behind the cluster. Would this be tapping into the brown wires and running a wire to a known good ground? Complaint, the wires that pug into the back of the cluster are awfully short. I almost thought about adding more wires to both of these to make it easier to plug the cluster in. I need to get to the gas tank in the trunk to check the sending unit it has been awhile. Thanks for your help.
 

eriknetherlands

Well-Known Member
Site Donor
Messages
2,015
Reaction score
1,232
Location
Netherlands, Eindhoven area
Sounds like a ground issue as you have two gauges that give up a the same time.
I'd first target the ground, as that is easy to do, and only costs 30 minutes and zero beer money is wasted.

In my e9, (not sure about e3) There is a ground at the hood release handle, which I think sandwiches 3 ground wires crimped to brass eye's. Wire brush the A-pillar, and sand each of the 3 brass eyes.
Secondly, the fuel tank lever sender also has a local ground, located in the trunk, near the middle at inside where the licence plate sits. wire brush & sand that ground point as well.
 

Attachments

  • 20220120_212709.jpg
    20220120_212709.jpg
    283.1 KB · Views: 29
Last edited:

Dan Wood

Well-Known Member
Site Donor
Messages
571
Reaction score
460
Location
Newnan, Georgia
I assume they were working before. It might sound stupid but check your fuses. I had a similar issue on 2800CS and bad contact on the fuse was the issue. The fuse looked good but wasn't making good contact. IIRC it was fuse #7. Either way it is a good place to start.
 

rsporsche

Well-Known Member
Site Donor $$
Messages
9,412
Reaction score
2,590
Location
Atlanta, GA
@chope97 you might want to check the cluster wiring harness. one make sure that there aren't any cracks in the wiring and that they are plugged into the right place. the wiring starts at one side and goes to the other sequentially. @eriknetherlands has a very good point about the grounds - especially the fuel sending unit which uses resistance to control the reading. i would start with the ground and then see if you are getting readings at the sender - those are notorious for going bad and giving you bad readings.
 

Dick Steinkamp

Well-Known Member
Site Donor
Messages
1,562
Reaction score
1,682
Location
Bellingham, WA
You may be already doing this, but I found it easiest to drop the steering column before pulling the cluster. It gave me plenty of room to remove and replace the wiring and prevents scratching the top of the column. Of course if you still have a speaker under the speaker grill, that needs to be removed also.
 

chope97

Active Member
Messages
193
Reaction score
56
Location
Silver Spring, MD
So last night I took the sender out. the gas tank was full to the top. I shook the sender and nothing moved and there was some wire sticking out the side, It's bad. So now I am looking for a new one. Oh by the way when I ground the brown and yellow wire the gas gauge needle does move so the gauge does seem to be OK.
 

bavbob

Well-Known Member
Site Donor
Messages
2,760
Reaction score
1,150
Location
Boston, Ma
These can be repaired. I think there is a DIY by Leslie Wong, not here, he has a blog that is old but still up.
 

chope97

Active Member
Messages
193
Reaction score
56
Location
Silver Spring, MD
Ok Bob I have about three broken sending units. If I send them to you with the wire will you fix them? Yes I refer to Leslie Wong's site often. You have those special hands made for a job like this. Just kidding but I would be glad to pay someone to fix them. I was told that the part is NLA even though the E( part is still available.
 

bavbob

Well-Known Member
Site Donor
Messages
2,760
Reaction score
1,150
Location
Boston, Ma
Sounds like you have nothing to lose. Open em up, take a peek, slide may just be hung up.
 
Last edited:

chope97

Active Member
Messages
193
Reaction score
56
Location
Silver Spring, MD
The one in my 73 I found the bottom nut had fallen off and the cylinder was crooked rendering the float to always be at the top even when it was empty ask me how I found that out
 

chope97

Active Member
Messages
193
Reaction score
56
Location
Silver Spring, MD
Sounds like you have nothing to lose. Open em up, take a peek, slide may just be hung up.
once again you are right, last Sat I cleared out the truck, twisted the sender out (gas tank was full what a mess) I shook it no movement, I took it a loose and found all wires intact, I clean everything with alcohol plugged the wires up and turned the ignition to on and it worked. Now I have to siphon some gas out and I ordered a new O ring for the final re-install. I found I have a good spare but it is longer than the one in the 71. Might fit my 73. thanks Bob for the encouragement, this car sat in my yard for 10 years before I got it on the road. I did use POR 15 to reseal the gas tank but did not think to take the sender a loose to clean it. on to the next thing
 
Top