Need help with ground problem.

[Mike G]

A while back I took apart the dash in order to replace the speedo needle, cable and a non working speaker on my '71. When I went to put the dash back in, my tach and speedo lights no longer worked. Looks like I messed up a ground wire somewhere as I can get the lights to work when I turn the light switch on and ground each of the lights housing to the chassis using a separate wire.

There is a ground on the left side above the kick panel with two black wires and they look to be OK. I also noticed that each of the tach and speedo have a ground wire that clip onto the back of the speedo and tach each. I tried to ground those wires separately, but nothin happened.

How do I trace or figure out which ground wire is the one that I messed up. Can anyone help me go through this systematically? I'm lost!!!!

Thanks.

[Verle R.]

Re: Need help with ground problem.

Do other lights on the dash work?
Do lights in the oil, fuel, clock, .... work?

Verle

[Mike G]

Re: Need help with ground problem.

Yes, the pressure, clock, etc. lights work and can be dimmed by the dimmer. Also, the emergency brake light works. The only ones that do not work are the turn signals and the tach and speedo lights (blue wires and gray wires).

Thanks.

[William C.]

Re: Need help with ground problem.

Wiring diagram shows a Ground on the speeedo and one on the tach. Tach side looks like a ring terminal, speedo looks like a plug onto a blade. Both black wires.

[Mike G]

Re: Need help with ground problem.

I can see these wires and connection points to the back of the dash. Both are blade type connections. The key question is do these ground connections need to be connected in order for the lights to work. I have manually tried to ground both of these and the lights still do not come on.

Any other ideas?

[William C.]

Re: Need help with ground problem.

Yes, they need to be connected.

[A L.]

Re: Need help with ground problem.

Mike, in your OP, it was indicated "I can get the lights to work when I turn the light switch on and ground each of the lights housing to the chassis using a separate wire.". In your last post, it is indicated, "I have manually tried to ground both of these and the lights still do not come on." If I am following your post correctly, the OP would indicate you have a ground issue and the follow-up post would indicate you have a supply voltage issue.
The easiest way to trouble shoot your problem is with a volt-ohm meter. Determine if you have voltage to the center connector of a couple of the light sockets(lights have to be on and best to have dash light brightness turned to max to get a readable voltage, probably 6 to 12 volts),if voltage is there, then check the continuity(a couple ohms or less) of the black ground wires to determine if in fact they are connected to ground.
To answer your key question, yes the black ground wires have to be connected to the blade connectors on the back of the tach and speedo housings. I suspect the tach and speedo cables could provide grounds but would not want to rely on it.
Once it is determined that there is voltage and a good ground, the only things remaining are the bulbs and bulb sockets. I would doubt if the all the bulbs and sockets went bad at the same time.
On a side note, if it was found there is no voltage,check the fuses.
A.G.

[Stephen L.]

Re: Need help with ground problem.

GROUNDS MUST BE CONNECTED.

Are the bulbs OK? Did you replace these while doing your repairs? Replace with a known good bulb (one that definitely lights) as a test.

Check to see if the bulb sockets have 12v present.
Make sure the ground wires are good. (Check continuity of the ground wire terminal to a good ground on the car)
Check continuity of ground lug to the metal tach/speedo cases. (Possibly assembled with an isolating washer or something by mistake)

[Mike G]

Problem Solved!! Thanks.

Yes, the ground wire must be connected to the tach and speedo housings in order for the lights to work. What threw me off a little was that the brake light, which comes from the same harness group of wires was able to go on. What I failed to understand was this light has two wires, obviously completing the electrical circuit on its own without the need for the other ground.

Ah, the joy of learning new things. Thanks for being able to bounce this off you guys.