Recently had new floor and trunk redone. rear tailights and backup lights worked beforehand. Now they don't. Spent all afternoon checking the wiring, couldn't see anything obvious. Replaced fuse and current was crossing the fuse because my tester light lit up on right side of the fuse. This mean power is going out of fuse box to rear of car. Somewhere in between something is not connected. 1) Is there another fuse in the trunk or under the back seat? 2) Is there a ground wire that I need to check in the trunk? Front headlights work and front turn signal lights are on constant, but no turn signal. I know there is a mutliwire harness under the floor going to the back of the car for brakelights and backup lights..they took good care to preserve it and hooked it back up when work completed.
Second problem...my tachometer needle no longer register rpms even though it lights up with dash at night...do I take tach out and send it somewhere to be fixed? It plugs into a harness that has several wires going into it. How can I check to see if it works?
Third problem. Gas guage: when car is off, the needle sits on 1/3 full. When I turn ignition key gas guage flips to far right and stays there until car turned off. I replaced sending unit at the fuel tank thinking that was bad...any ideas on this one?
So three separate electrical issues, appreciate anyone's kind help with these issues.

 

I'm not positive on the 1964, but I know on newer years there's a ground strap that attaches to the square piece that the trunk latch connects to when you close the trunk. It should be part of the tail light harness. There shouldn't be any connections under the seats. Back to the late 1960's I know theres a connection under the quarter panel near the inner fenderwell on the drivers side. I've got a 1964 but I've not begun to restore it yet so I can only say what I've seen on late 1960's. Your description of the gas gauge also sounds like a bad ground.

If someone can tell you how to test the tac I'd try that before taking to a shop. John

 

Around the drivers side rear inner wheelhouse, there should be a wire that separates from the ribbon harness.
That should be the ground - make sure it's a clean connection to the trunk floor.
Same with the gas guage - check the ground wire off the sender!

2blue - guess we think alike - I was watching a show + typing, got distracted, so I took awhile1

 

I checked where the trunk latches, no ground wire. Checked the rear quarter panel fenderwell and no ground wire there either. There is a harness with four wires wrapped that is connected to the right tailight, then left taillight, and backup lights, then wire goes down the back of the seat towards the front of car. I am getting positive current at the brake light switch so there is a disconnect between that point and where the rear wire exits the back seat going back towards the tailights. Have looked thoroughly under car and in trunk and fenderwells, no ground wire.
I checked the ground wire for the fuel guage, still not working so will undo the dash and check the back connections of the fuel guage in the dash itself.
I appreciate your input..THX JM

 

Is this rear inner wheelhouse the left rear wheel well? Is it the inside where the tire is or is it the exterior of the rear wheelwell that you see looking to the left into the trunk? Don't see any wire in trunk that connects as a ground. There is a four wire harness starting on the right tailight,coming around to the left tailight with a wire branch off to the reverse light and trunk courtesy light. This wire harness continues into the area behind the power top motor behind the back seat. So the harness continues under the carpet to the front where it connects to brake light switch. I did find positive current at the brake light switch. So there is a disconnect between that point and where the harness exits the backseat area into the trunk towards the brake lights. Checked the ground off the sender, but the gas guage needle still to the right..going to remove dash and check connections at the fuel guage. I appreciate all your input here. THX JM

 

If I can get home from work in time tomorrow night I'll check my 1964 I'll try to see what it has in the trunk harness. John

 

This turned out to be a simple issue. At the front behind the fusebox there is a connection that brings power to what is called a "ribbon cable" that is flat and has flat copper wire inside of it. The plastic plug was loose and the copper teeth from the ribbon cable were loose. Tried to put it back in straight, but may try to use a replacement ribbon cable to solve the problem. Got all lights to work except for the reversing backup lights. Will check that connection in the transmission shifter as there is a switch there. The fuel gauge worked for about ten minutes and then went back where needle stuck to right. I think once I try a new ribbon cable with a tighter connection at each plug, I should be okay.
Thanks to all for their input on this issue.