[JAL69Z]

I know this is a very old post but maybe you can help. My 69Z console is having an electrical gremlin..[when I turn on the rs headlights both the temp and the gas gauge stop working. This is a new recent development and has no mods to it. I just purchased the wiring diagram and hope it will get here soon. Would you have any ideas why this would be happening? No expert here by any means on electrical gremlins. Does this sound like a bad ground or? I took off the plate but nothing seems out of place, I did notice one black wire that appears to be the only ground.

 

[JAL69Z]

Does it have factory gauges? Never the less I'd be looking for a loose or bad ground to the gauges. Also check the voltage regulator mount on the firewall if it still has the old stuff on it.

It does have all the factory gauges, nothing altered at all. I was thinking loose ground as well...will look at the back of the console to see if i can see anything. Checking the voltage reg as well..thanks!

 

[JAL69Z]

My guess is also a console ground issue. Based on the wiring diagram (one from Larry Dubois - excellent!) , the gas gauge and temperature gauge share a ground with the console gauge lights. Maybe when the console lights go on with the headlights, the console light's current through the shared console ground is causing an issue. (Note, the stock oil pressure gauge and ammeter do not use this ground).

Are the console gauge lights working properly when you put the lights on?

Do the gauges work if you turn the gauge/dash light brightness all the way down by turning the headlight switch knob all the way? This will reduce the ground current due to the console gauge lights.

Do those gauges work properly if you only turn the parking lights on?

Hope this helps,
Bert

Bert..thanks....the console gauge lights do not come on at all as well as the temp and fuel gauges not working as I pull out the headlight knob. Once the headlight knob is push back in the gauges work fine except the light bulbs in the console cluster. Strange tho that the end of the console light in the rear works fine. Based on your reply and others its seems like i need to trace the ground wire and make sure something hasnt come loose. The one ground wire I did see look fine and is located on the top of the housing. I havent tried your suggestion on the parking lights and dimmer yet but will later today.
Really appreciate the help here!
Jim

 

[JAL69Z]

The console courtesy light bulb is fed by always hot 12V "battery" (orange wire - fed through a fuse). This bulb is turned on by being grounded through the door switches or the courtesy light switch in the headlight switch. So it is on a separate grounding circuit so I am not surprised it still works.

Be sure to let us know what you find.

Bert

The console courtesy light bulb is fed by always hot 12V "battery" (orange wire - fed through a fuse). This bulb is turned on by being grounded through the door switches or the courtesy light switch in the headlight switch. So it is on a separate grounding circuit so I am not surprised it still works.

Be sure to let us know what you find.

Bert

Will do...look hopefully before the end of the week.
Thanks!

 

[JAL69Z]

DaytonaYellow:

Be careful - the wires to the ammeter gauge are connected directly to the battery (through fusible links) and are always hot.

You should make sure the gauge pack is grounded before turning the lights on else the ground side of the fuel and temp gauges will be pulled close to 12V through the bulbs since you have no chassis ground connected. I do not know if this can damage the gauges or not.

Looks like you are missing the ground. There should be a THINNER black wire with an eyelet coming out of the console wiring harness (NOT the ammeter wire). I believe this ground eyelet is attached with a screw to the back of the gauge pack on the metal mount between the ammeter and the temp gauge. It is hidden in your picture.

Here is a pic of an aftermarket gauge similar to the original. You can see where the black ground is attached on this unit at the bottom center between the ammeter and the temp gauge connectors. I believe the original connects the same way. This matches how it is shown in the AIM.

View attachment 320125 View attachment 320126

If you can not find the ground wire from the console harness you can do what Fairfax1000 suggests and just add a new/additional ground wire from that screw hole or that empty ground stud above the fuel gauge connector on the back. Just make sure you connect it to a good ground on the car on the transmission tunnel.

The stock gauge pack has two separate metal mounting brackets - one for the fuel and oil and one for the ammeter and temperature gauges. The two should already be connected together internally.

Bert

Really great info for me as well....my ground strap is on top of the gauge housing and I have not taken the gauge housing out to look underneath it. I will look to see if I have the ground attached trans tunnel.
Great pics.

 

[JAL69Z]

Hi,

JAL69Z and DaytonaYellowZ - did you ever get you gauge issue sorted out?

Unfortunately for me no success. Grounds appear to be fine and have good contacts. I tried grounding the gauges with a jumper wire and had no effect.

Not sure what else to do at this point, just really puzzled two of the gauges work and the other two don't.
Just love electrical gremlins.

 

[JAL69Z]

The oil pressure gauge is mechanical and is fed oil pressure directly with a tube from the engine. Other than possibly its gauge light, it will have no affect on the other gauges.

The Ammeter is wired separately into the engine compartment and connected across the charging wire from horn relay buss bar (or junction in the harness near there - I do not recall) and the battery junction near the battery. It is connected to these points through fusible links and actually monitors the voltage drop across this wire. The Ammeter is floating relative to the console gauge power and grounds. It should not affect the other gauges when the lights are turned on (except again possibly its light). These leads are always hot so be careful with them.

Do the Temperature and Fuel gauges have any reaction when you turn on the headlights on with the ignition OFF?

Can you measure the Ignition Power voltage at the Fuel or Temperature Gauge connector with a voltmeter with Ignition power on and the Headlight Switch on and off. Vary the dash light dimmer as well

You could try to remove the small 4 or 5 amp "Instruments Lamp" fuse and then try the headlight switch. Removing this fuse will isolate the Instrument and Console Gauge illumination lights from the headlight switch. Then check the gauges operation. Vary the dash light dimmer as well. If the gauges are OK with the fuse removed you have tied the problem to the console gauge lights. If no change then it is something else. Here is a snapshot of the fuse panel from the 68 AIM but I think the 69 is the same.

Let me know.

View attachment 320860

Geez Rs-man you really know your stuff and thanks for helping me out on this! To answer at least one of your comments/questions, dimming doesn't do anything to help the situation. With the engine off the fuel gauge pegs below E and the temp goes past H. None of the console gauge lights work when I turn the engine on and turn on the lights to the dash etc. Will definitely try the other suggestions as quickly as I can in a few days.
Thanks again,
Jim