Team,

Gauges on my 79 have been perfect since I refurbed the cluster board a while back...all instrument lights work, all gauges read appropriately (even the clock on a good day).

Yesterday, shortly after I turned on my headlights, the oil pressure gauge dropped to zero and the amp gauge was showing less than full charging at highway speed; even the gas gauge was bouncing a tad. Temp seemed OK. The oil pressure rebounded, as did the amps, but both were flaky and sporadic. Alternator belt is fine, as is oil level. Car ran great. Cluster lights all OK.

History: I recently installed a newer lighter socket from a modern mini-van - no issues at all; all still worked great including new lighter (I had a bad ground on the original that kept blowing the fuse so I took it off line until I could replace it)

Shorthly thereafter I lost retraction function on my power antenna; goes up fine, but no response when HU shut off so need to retract by hand.

I recently lost the retention on my left turn signal (won't hold when cliked down): Column refurb pending

Question: Are any of these failures related? I know the antenna and lighter feed from the same central harness so I can imagine I may have tweaked some antenna wire when playing with the lighter. But I can't see how I would have impacted the gauges, especially all of a sudden and seemingly coinciding with turning the headlights on. Is there a common ground in and around the tunnel that could be the issue?

Woah is me...time to save the pennies for a full harness replacement. I hate old wiring...

Thanks for any thoughts,
Steve

 

The statement bad ground was blowing fuses concerns me. Bad grounds don't blow fuses. The gauge symptoms point to a bad ground though. I would look closely at the plug in on the gauge cluster. The tabs on the printed circuit board tend to pull loose when removed. Glue them all back into their proper positions if they are loose.

 

Agreed...worded poorly. The socket was shorting out; the outer, grounded shield was contacting the inner, hot sleeve somewhere. Never had an urgent need to spark one up so decided to disconnect. New socket with it's isolated ground config worked perfectly.

I'll check the plug at the board...I was rooting around in there a bit but not too much. I suppose if the clip was in, but not fully locked, it may have worked its way loose.

Any other thoughts, especially the association with the headlights? Coincidence? I know the cluster lights route through the light switch but I'm not sure about the gauges (and my apologies, I haven't had a chance to peruse the wiring diagramn yet...)

 

The tie to the gauge panel from the HL switch would be the panel lamps. If they are feeding back through a bad ground it could cause erratic gauge function, or if one of the tabs is bent over and touching another, it could cause problems. So, there is a connection to the HL switch.

 

If you're experiencing these issues and blowing fuses, I would suspect a hot partially shorting to ground, e.g. a wire with worn insulation against a grounded part of the car.

 

Please elaborate...



Update: no improvement in gauge function yet

Clarification: I am not blowing any fuses...my amp and OP gauges in particular are sporadically erratic, seeemingly when lights are on. All else works fine

1. repaired left turn signal issue; no change to gauges

2. Interesting new finding...I start the car and test all the turn signal functions with the headlights off. Everything seems OK. However, when I turn on the lights the inner rear passenger side signal blinks weakly and out of sync (ie when the outer is on , the inner is off, and vice-versa). The culprit? I'm thinking of swapping out the socket but I know the rear lights have their own ground point and don't know if a bad socket could influence the gauges

3. I had coupled the ground from the lighter with the ground from the antenna, using the wire that the original lighter connected to. I removed the lighter from the loop to see if antenna and/or gauge function would restore; no to either

4. The antenna relay is giving the signal when the radio is turn off, just no down function on antenna...I think the antenna may be bad, and I don't suspect it is causing the gauge probs. I will likely replace antenna to remove relay

5. Bonus: Found the connection at the base of the column for cruise control; disconnected it and found the spades on the connector were corroded; cleaned up and reconnceted, now cruise control works


Assume the headlights are not the culprit...any other thoughts?

Thanks for your patience...I've been over the wiring diagrams but I confess I have a hard time following them. I need to get one of those real world ones that shows the actual wire, not the schematic

Smiles, Steve

 

Guages- easy to not have a good connection (can be cleaned w/ pencil eraser) to the printed circuit.

Sounds like 4 tail lights which would be a mod., bulbs, wiring & socket should be checked. 2 element bulbs & sockets needed to do it right. I also changed the flasher for 4 tail lights.

 

Update:

Pretty sure the antenna is NG. Will likely replace but OK for now.

I replaced one of the rear sockets (yes, 4 bubble-light mod...good call!). Lights work great, gauges still sporadic.

Got a good inspection of the rear of the cluster...no issues, buttoned up tight, good contact.

Checked the ground at the alternator...uh-oh...kinda cruddy and corroded. Cleaned up the ground conncetion

While cleaning up the battery lead I inadvertenly loosened the internal nut that holds the battery post and had to do a disassembly of the alternator (major D'oH). Unfortunately I trashed the spade going from the windings to the center triode when separating the cases. I swapped in a back-up unit I had on the bench and behold, all is well! Gauges dead-on and smooth, with or without headlights on.

Bottom line...either alternator was bad to begin with and I serendipitiously discovered the prob (it was purchased used) or cleaning the connection points for the battery and the ground wires cured it. Regardless, I'm good to go.

Thanks to all, Steve