Tach, oil pressure, oil temp Gauges stopped working!

[rennch]

Hi all,

It's been a while.

A while ago, my gauges stopped working. My tach spent one day jumping around, (It's got an MSD tach adapter and an MSD box) and now doesn't move at all. My oil temp and pressure gauges, that once worked, are not working either. I remembered recently that I installed a "modern" 12v socket so I could charge my iPhone. I'm wondering if I might have shorted something in the process. Is there a commonality with those gauges?

Thanks!

Mike

[Bobboloo]

You either lost 12v+ or ground. Usually when you lose ground the gauges will peg. If that's not the case then 12v+ is probably gone. Your iPhone install could be the culprit.

Have you checked your fuses?

[rennch]

I've checked the fuses...I'm trying to backtrack and go back to ground zero at the moment, though I don't really know how to use the voltmeter. Googling that now. :0

[dshepp806]

Originally Posted by emptyo

Hi all,

It's been a while.

A while ago, my gauges stopped working. My tach spent one day jumping around, (It's got an MSD tach adapter and an MSD box) and now doesn't move at all. My oil temp and pressure gauges, that once worked, are not working either. I remembered recently that I installed a "modern" 12v socket so I could charge my iPhone. I'm wondering if I might have shorted something in the process. Is there a commonality with those gauges?

Thanks!

Mike

depends on how you "wired" into the circuit....how did you wire this "socket"?

Doyle

[rennch]

I've made zero progress on this front, and would love anyone in Denver that's handy with this kind of thing to perhaps give me a hand with it. I'm fairly useless when it comes to electrical stuff.

[rennch]

Can anyone offer any insight on how to test the gauges? The circuits?

[fintstone]

I am travelling and do not have a wiring diagram...so I cann be specific but, generally speaking, most cars have all gauges running off the same power/fuse and the actual changing inputs are from senders that change resistance on an external ground. What this means is that if more than one gauge goes out at a single instant...it is almost always ith fuse or connection on either end of that wire.

[86 911 Targa]

Originally Posted by Bobboloo

You either lost 12v+ or ground. Usually when you lose ground the gauges will peg. If that's not the case then 12v+ is probably gone. Your iPhone install could be the culprit.

Have you checked your fuses?

+1.

I do not have a CKT for your year/model, however, I would first check the fuses, then if all is well, remove your modifications, and see if your gauge functions return.

Good luck,

Gerry

[rennch]

Yea, I've done the "reversal" plan, to no avail. I'm stumped.

Curious...what's a CKT?

[86 911 Targa]

Originally Posted by emptyo

Yea, I've done the "reversal" plan, to no avail. I'm stumped.

Curious...what's a CKT?

CKT=circuit diagram.

I have one for our '86 which is most probably not compatible with your year/model.

Gerry

[hessel1974]

Have you figured out how to use a volt meter yet?

I would pull the meter from the dash. On the back you have 3 types of terminals: 12V+, ground and "G". "G" are the wires which come from either the Oil temp sensor & Oil pressure sender. This is not what you should look for.

Set the voltmeter in such a way to measure 12V. Turn the ignition to the first step. This will normally power the meters. Check if there is 12V on the + terminals.

If so, you have a ground problem. If not, you will have to dive deeper into the wiring diagram to track back where the current is lost.

These problems can be very tedious, but a case of trace and elimate causes.

[woland]

Hi

Maybe you can find some help in this thred:

Wiring all the gauges in a 911 SC

Anyway in your car the things cannot be much different from my SC exept for the speedo. Every gauge and tach have a 12V wire (red and black), a ground (brown) and a sender wire (different color for each wire).

How to work with the ohmeter:
You set in at 0-20 VCC and connect the red with 12V and the black with ground. Probably you will find no tension.
If the clock works (clock has a separate 12V working alltime) try to switch this wire with the 12V wire of a gauge and see if it works.

I think that's not prabable that ALL the gauges died at the same moment.

I saw all your work but tried to see your t-shirts I'm not allowed. Why?

[rennch]

Current state of affairs:

power off | Power on

fuel gauge: Ok. | Ok
Oel gauge: Bottom | pinned

temp: Bottom. |. 120
pressure: Bottom | pinned

tach (w/msd). Nothing | nothing
speedo Stuck at 30 mph | doesn't move

that's what I've got currently.

[rennch]

Oh, and all fuses intact.

[hessel1974]

You can check if the gauge is working when you take the sender wires from the senders and groung these to the engine block. When these are grounded, the gauge should be pegged to the top. If this is the case, they work.

Perhaps a good idea to check this. Don't forget to switch the ignition on so that the gauges get power.

[pete3799]

There's a ground behind the ash tray with several brown wires going to it .
Clean it and see if that helps. See if there's any loose wires in that area.

[rennch]

I'm going to check the grounds behind the ash tray. I'm feeling more and more like this is a ground issue.

[86 911 Targa]

Originally Posted by emptyo

I'm going to check the grounds behind the ash tray. I'm feeling more and more like this is a ground issue.

We still do not know where you connected your iPhone.

Here is the wiring diagram for the '84 3.2.

Disconnect the ground(s) to your gauges individually, and test for continuity to ground.

Then disconnect the +12V wire(s) individually, and test for +12V.

I think that pete3799 is close.

pm me.

Good luck,

Gerry

[rennch]

All I did is swap out the OEM cigarette lighter with one from radio shack. Same two connections on it... The OEM one was a little bigger and the adapter was loose in there, so I just swapped for a more modern, smaller one. It's got the same exact specs as the OEM one...ground is on the outside body, 12V goes to the center.

I just pulled the gauge that has the pressure and fuel. Don't ask me to do that again...what a colossal pain to get behind the dash. Anyway...I pulled it, and in the cockpit, tested the ground with a fresh wire grounded to the chassis in a couple different spots. No change yet. I really think I need to bring someone in on it...I can't imagine that all the senders would have failed simultaneously. Thanks for the help thus far, all.

[fintstone]

It is likely not the ground or senders or wires to either. It should be something that all gauges have in common. Generally speaking, most cars have all gauges running off the same power/fuse and the actual changing inputs are from senders that change resistance on an external ground. What this means is that if more than one gauge goes out at a single instant...it is almost always the fuse or connection on either end of that wire...so follow the 12v wire red/black in the schematic above.