Many Instrument Gauge issues on a tach dash

[Super Birthday Snake 11]

So got my car on the road but I have the following issues (pretty much everything) with my tach dash:

 

1. Speedo doesn't work, assume it's fell out one end so no big deal

 

2. Tach doesn't work correctly, does move but won't go over 1000 no matter how high it's rev'd

 

3. The bulb at the right side of the tach doesn't light, neither do the full beam, engine warning or any other warning/indicator lights. Turn signals work fine.

 

4. Fuel gauge doesn't work.

 

5. Temperature gauge doesn't work.

 

I replaced the CVR with a solid state one which made no difference. Could any of the gauges grounding against the housing cause this?

 

I've got a new printed circuit which I've heard can be crap as well.

 

Tried flipping bulbs for the light issue.

 

Thanks in advance!

[69volunteer 84]

May want to start with one issue and then try to solve backwards. I am trouble shooting my gas gauge (new AAW wire install) and was able to determine it is either my tank or sending unit by grounding the feed at the sending unit.

[SA69mach 39]

Speedo - remove the sender unit from the T5 (you can do it from under the car with the T5 in place. Check you have a drive gear on the end of the cable. If YES, poke a finger in the trans and feel for a drive gear on the SHAFT of the trans. (You might use a small mirror and a flashlight to do the check too)

 

If it looks good with both trans gears in place, try twirling the drive gear by hand (or a very slow drill speed, and get someone to observe the speedometer in the car. Does it register?

Yes - then you have a problem with the trans gears

No - move to the rear of the speedo

 

You have obviously removed the dash panel before, so make sure you have the white plastic "ring" in place to hold the speedo end of the cable into the back of the speedo.

I have messed this up before, and failed to get the square shaft into the back of the speedo properly seated, and also did not get the weird plastic clip in place. The clip goes on with a odd rocking motion, you have to push it off center and then onto the back of the speedo, and it locks in.

 

If that is in place correctly, it could be a problem with your internal drive gear inside the speedo. Small nylon cogs which can have the teeth all chewed off. It is pretty easy to disassemble the speedo once it is out, and you can examine the internal gears, see if you can spot a problem.

 

this is a mechanical system, so something is not connected right, or it is chewed up.

 

2. don't know about the tachos

 

3.You got power to some parts of the circuit board, because the indicators are part of that. Some of the bulb carriers fail when put into the circuit board. I have rebuilt my dash instruments twice and you just gotta get onto the bench with a test light, a battery, some leads and test everything. Test a bulb carrier, then put in a bulb, then another bulb, and so on, until you find all the good ones. When you have a good circuit on the board, and you insert a good bulb carrier and a good bulb, it should work right? Hmmm sometimes it just needs a twist or a tweak to make it work. Dash lights have to be chased hard to get them all working.

 

4. fuel gauge - two identical fails on my 69 and 70. Low level, sluggish activation, just tired gauges. I have tested my wiring, grounds, senders, IVR. replaced all for new. Tested all components before installation, added extra grounding wiring, tried the potentiometer test. All showed the gauges should work. So far, still showing low for both. Next step should have been my first step NEW GAUGE. They wear out. You may have better luck and more fun testing and replacing everything except the gauge than I did.....

 

5. Ditto the temp. gauge. You may want to do the standard circuit testing and grounding test for both fuel and temp gauges. they are easy. Switch the ignition ON. Remove the wire and cap from the temp sender and ground the wire on the block or the chassis. The gauge should peg past full. (Only do this for a few seconds or electrical/gauge damage can occur) if you want to go further testing the gauge, if it pegs out, is to borrow a potentiometer and apply known resistance to the sending wire. 78 ohms should be 'empty" and 10 ohms should show 'full'. That is the range for 69 and 70 temp and fuel gauges.

 

I have been messing around testing and trying to fix my fuel gauge and temp gauges on two cars for about a year. Most other owners with this particular problem have bought repro gauges and they fixed the problem. Just saying.....

 

Your issues are not necessarily related to each other. the speedo is definitely NOT electrical problem. Bulbs, IVR and circuit board are probably related.

 

You must be sure to isolate and insulate your temp and fuel gauges from the housing. there is some cardboard spacer/insulators that should be in place between the gauge and the housing, as well as plastic caps . That could well be the reason why both those gauges are dead. if they don't register with the grounding test then that is a strong possibility.

 

Long post - but, it is tricky to fix all the things you have listed. You will have to find the fault and make the best repair you can, one by one.

 

I have used tachman.com for some gauge restoration and he is a good guy. There are others, and all the parts are available, either used old parts or reproductions.

 

Good luck. let us know how you proceed and how it works out. it is a weak part of the 69 and 70 Mustangs and very common to have problems. Remember - most people find solutions with new gauges - usually after doing all the testing and work I have suggested. Your call.....

[SA69mach 39]

May want to start with one issue and then try to solve backwards. I am trouble shooting my gas gauge (new AAW wire install) and was able to determine it is either my tank or sending unit by grounding the feed at the sending unit.

 

 

I have found that the grounding test gives a false positive on the function of the gauge. If it pegs out I don't think that means the gauge is 'perfectly good'

I have spend many hours trying to fix my fuel and temp gauges and associated components with all the standard tests. I think the grounding test just shows it has power, and will peg out - nothing more. I have replaced and restored every portion of fuel and temp sensing systems in two cars now, and all four gauges pegged out when grounded, and still read low and erratic.

 

My opinion now, after all the work, is that is the gauges themselves. I fixed every other component of the clusters that were not operating correctly. the gauges just will not play fair. they are all faulty. Hard lesson learned.

[Super Birthday Snake 11]

I have found that the grounding test gives a false positive on the function of the gauge. If it pegs out I don't think that means the gauge is 'perfectly good'

I have spend many hours trying to fix my fuel and temp gauges and associated components with all the standard tests. I think the grounding test just shows it has power, and will peg out - nothing more. I have replaced and restored every portion of fuel and temp sensing systems in two cars now, and all four gauges pegged out when grounded, and still read low and erratic.

 

My opinion now, after all the work, is that is the gauges themselves. I fixed every other component of the clusters that were not operating correctly. the gauges just will not play fair. they are all faulty. Hard lesson learned.

 

Speedo - remove the sender unit from the T5 (you can do it from under the car with the T5 in place. Check you have a drive gear on the end of the cable. If YES, poke a finger in the trans and feel for a drive gear on the SHAFT of the trans. (You might use a small mirror and a flashlight to do the check too)

 

If it looks good with both trans gears in place, try twirling the drive gear by hand (or a very slow drill speed, and get someone to observe the speedometer in the car. Does it register?

Yes - then you have a problem with the trans gears

No - move to the rear of the speedo

 

You have obviously removed the dash panel before, so make sure you have the white plastic "ring" in place to hold the speedo end of the cable into the back of the speedo.

I have messed this up before, and failed to get the square shaft into the back of the speedo properly seated, and also did not get the weird plastic clip in place. The clip goes on with a odd rocking motion, you have to push it off center and then onto the back of the speedo, and it locks in.

 

If that is in place correctly, it could be a problem with your internal drive gear inside the speedo. Small nylon cogs which can have the teeth all chewed off. It is pretty easy to disassemble the speedo once it is out, and you can examine the internal gears, see if you can spot a problem.

 

this is a mechanical system, so something is not connected right, or it is chewed up.

 

2. don't know about the tachos

 

3.You got power to some parts of the circuit board, because the indicators are part of that. Some of the bulb carriers fail when put into the circuit board. I have rebuilt my dash instruments twice and you just gotta get onto the bench with a test light, a battery, some leads and test everything. Test a bulb carrier, then put in a bulb, then another bulb, and so on, until you find all the good ones. When you have a good circuit on the board, and you insert a good bulb carrier and a good bulb, it should work right? Hmmm sometimes it just needs a twist or a tweak to make it work. Dash lights have to be chased hard to get them all working.

 

4. fuel gauge - two identical fails on my 69 and 70. Low level, sluggish activation, just tired gauges. I have tested my wiring, grounds, senders, IVR. replaced all for new. Tested all components before installation, added extra grounding wiring, tried the potentiometer test. All showed the gauges should work. So far, still showing low for both. Next step should have been my first step NEW GAUGE. They wear out. You may have better luck and more fun testing and replacing everything except the gauge than I did.....

 

5. Ditto the temp. gauge. You may want to do the standard circuit testing and grounding test for both fuel and temp gauges. they are easy. Switch the ignition ON. Remove the wire and cap from the temp sender and ground the wire on the block or the chassis. The gauge should peg past full. (Only do this for a few seconds or electrical/gauge damage can occur) if you want to go further testing the gauge, if it pegs out, is to borrow a potentiometer and apply known resistance to the sending wire. 78 ohms should be 'empty" and 10 ohms should show 'full'. That is the range for 69 and 70 temp and fuel gauges.

 

I have been messing around testing and trying to fix my fuel gauge and temp gauges on two cars for about a year. Most other owners with this particular problem have bought repro gauges and they fixed the problem. Just saying.....

 

Your issues are not necessarily related to each other. the speedo is definitely NOT electrical problem. Bulbs, IVR and circuit board are probably related.

 

You must be sure to isolate and insulate your temp and fuel gauges from the housing. there is some cardboard spacer/insulators that should be in place between the gauge and the housing, as well as plastic caps . That could well be the reason why both those gauges are dead. if they don't register with the grounding test then that is a strong possibility.

 

Long post - but, it is tricky to fix all the things you have listed. You will have to find the fault and make the best repair you can, one by one.

 

I have used tachman.com for some gauge restoration and he is a good guy. There are others, and all the parts are available, either used old parts or reproductions.

 

Good luck. let us know how you proceed and how it works out. it is a weak part of the 69 and 70 Mustangs and very common to have problems. Remember - most people find solutions with new gauges - usually after doing all the testing and work I have suggested. Your call.....

 

That's some excellent advice, really appreciate you taking the time for that.

 

New gauges would be the ideal, particularly aftermarket ones but unfortunately I just don't have the money for them.

[69gmachine 15]

It has been my experience that the gauges seldom go bad. Most often it is the sending unit or the wiring. I don't know what constitutes "perfectly" good, but if it passes the grounding test and goes full scale, then try using a 30 ohm resistor to make it go half scale to convince yourself to look elsewhere.

 

As for the tach, it sounds like it's shot. This is the exact same failure mode mine exhibited. I would consider upgrading to a 3 wire tach conversion. The factory tach carries the current to the coil so you don't want to keep driving on it waiting for it to completely fail.

 

The speedometer is most likely disconnected at the dash cluster (but you should do the verification tests to make sure nothing is missing). Remove the dash cluster. Disconnect the cable at the tranny so you can pull enough length through the firewall to establish a solid connection to the cluster BEFORE you bolt it back in place. It's very difficult to ensure a good connection while it's bolted it.

[Super Birthday Snake 11]

It has been my experience that the gauges seldom go bad. Most often it is the sending unit or the wiring. I don't know what constitutes "perfectly" good, but if it passes the grounding test and goes full scale, then try using a 30 ohm resistor to make it go half scale to convince yourself to look elsewhere.

 

As for the tach, it sounds like it's shot. This is the exact same failure mode mine exhibited. I would consider upgrading to a 3 wire tach conversion. The factory tach carries the current to the coil so you don't want to keep driving on it waiting for it to completely fail.

 

The speedometer is most likely disconnected at the dash cluster (but you should do the verification tests to make sure nothing is missing). Remove the dash cluster. Disconnect the cable at the tranny so you can pull enough length through the firewall to establish a solid connection to the cluster BEFORE you bolt it back in place. It's very difficult to ensure a good connection while it's bolted it.

 

Thanks a lot for this. What does the 3 wire tach conversion involve?

 

I've definitely got a speedo gear etc. so the cable's either disconnected at the back of the gauge or the gearbox so will check that out.