Elec help with gauge

[look 171]

My tach, and the 2 left gauges are out along with my signal lights. It comes back on once in a while. Where would you start looking and what are the process of elimination? Speedo and boost gauge are fine. It is an 88 930. Crank fired. Are all the gauges on a single fuse? Something is loose somewhere but where would you start to track it down?

Jeff

[look 171]

anyone?

[kidrock]

I'd check my Bentley for fuses and relays, and follow through.

[dshepp806]

have you the Bentley?

I'll try to check mine this evening for data (fuses).


Best,

Doyle

[DRACO A5OG]

Lights or Guage readings?

Behind the Fuel Guage there is a ground connector, check that.

[look 171]

No Bentley but thanks for checking for me.

Drago, The gauges are dead, but the lights in the gauges are working. That leads me to think its not a fuse?

Jeff

[kidrock]

pull your fuse cover and check your fuses first. Your problem could be a fuse, relay, ground or maybe a sign that your voltage regulator is going kaput.

strongly recommend plunking down a c-note for the Bentley, probably the smartest $100 you'll ever spend on your ride.

[marks914]

Sounds like its a ground issue, the lamps usually have a seperate ground so they work.

Mark

[86 911 Targa]

look171,

Without knowing the circuit deficiency, (ground or +12V), or a Bentley manual, this would be a tricky issue to resolve.

Check/replace the appropriate fuse(s).

Sometimes, after long term use, these fuses become corroded at the fuse holder.

You should buy a Bentley ($35), and a Fluke 77 ($75) on eBay.

The Fluke is very handy around the car, and the house.

Good luck,

Gerry

[look 171]

Bently is in the works. Do you guys know if the gauges are on one ground, or each gauge has its own ground? Is that something I can see once I pull the gauges?

[86 911 Targa]

Jeff,

Page 970-82 of our Bentley shows a common grounding point for the instruments in question behind the tachometer. (G116).

After carefully pulling the tach and speedo, the connection(s) should be very accessible.

Also, verify voltage on both sides of fuse #8.

Good luck,

Gerry

[86 911 Targa]

Jeff,

Bentley on the way..........

In the meantime, try this link.

http://www.cannell.co.uk/Manuals.htm

Good luck,

Gerry

[sprintamx]

Another possibility is the ground strap on the transmission. My tach, oil pressure and temp gauges went whacky, and got worse when I turned on the headlights. Also, and I did not think this was related, the motor would struggle so much to start--even with a fully charged battery--that I thought my starter was going.

Checked the voltage at both the battery posts and the cables while running, all was well. Battery held a charge just fine. Fuses were fine, no corrosion. Could not detect any loose wires on the guages or any obvious cuts or gaps in the wiring. The guages are all on common power and ground, with the wiring disappearing into places I wasn't ready to go, so I was getting frustrated and seeing vissions of $$$ floating on the wind.

Turns out it was the ground strap. The guages now work correctly and the motor starts right up with strong engagement--literally night and day difference. Surprised the heck out of me that there was so much drain from a bad ground that the starter was working at about 1/2 its capacity. Also, and this could be just my excitement, the motor feels/sounds smoother and stronger. Stronger spark? Better injection, timing, something else from the DME? Dunno, but check your strap!

Aaron

[DW SD]

I would think along the lines of the ground on the instrument cluster. If the car doesn't crank, then think towards the ground strap from transmission to body.

Doug

[look 171]

Originally Posted by 86 911 Targa

Jeff,

Page 970-82 of our Bentley shows a common grounding point for the instruments in question behind the tachometer. (G116).

After carefully pulling the tach and speedo, the connection(s) should be very accessible.

Also, verify voltage on both sides of fuse #8.

Good luck,

Gerry

Gerry does it show a different ground for the right 2 gauges in the manuel or are they all grounded to the same spot? I will check this weekend and report back.

Thanks a bunch, guys.

Jeff

[86 911 Targa]

Originally Posted by look 171

Gerry does it show a different ground for the right 2 gauges in the manuel or are they all grounded to the same spot? I will check this weekend and report back.

Thanks a bunch, guys.

Jeff

All use the same ground (G116).

Please use the link I sent you.

Good luck,

Gerry

[scarceller]

I'd pull out the left hand gauge (Oil/Fuel) and simply test for power and ground on it. Try to figure out if it's the 12V feed or the Ground that's not making it to the gauge, this will allow you to know what to further investigate. Meaning are the gauges not working because they have a ground issue or a supply voltage issue.

First connect the test light to a known good ground and then test for the 12V source wire to the gauge.

Then flip the procedure, connect test light to known good 12V source then test the ground at the gauge.

Do all testing with no wires removed from gauges (trust me on this one) you really need to do all testing with the gauge load applied. Try to leave things as they are and don't start unplugging wires just yet. Reason for this is that if you have a corroded contact you really need the load (current draw) produced by the gauge to get the contact to fail. If you unplug the power and ground from the gauge and then test across these 2 wires with a DigitalVoltMeter very often the DVM does not draw any current and will measure 12V but the minute you plug the connectors back to the load (The Gauge) then you see no voltage (or low voltage) because it now has caused the bad contact to act up and the voltage is being dropped across the bad contact. Simple OHMs law here. The simple reason for this is that a good contact has 0ohms but a corroded contact could have 10000ohm resistance and if the only load is a hi-resistance DVM (1,000,000ohms) then the DVM will read near 12v but the minute you put a load on the circuit of say 1000ohms now things are very different. The corroded contact will have about 10v across it and the load (gauge) will only have 2v.

DVMs are not good choice to chase these problems down, they will only work if you use the DVM with the load still applied. Test Lights are better as they produce a load (the bulb). But in the end it's always best to test with the natural load applied.

Kind of long explanation but this will drive you nuts if you don't understand these principals. To often I've heard the story "I tested with the DVM and it has voltage, but when I plug it back in it doesn't work?".

[dshepp806]

clean those damned connectors real well.....

Should you get a situation that provides a suspected resistance (subsequent ohms law voltage measurement) producing a suspect voltage, then simply have a look at (measure) the contacts/connector resistance with the ohmmeter function.

Agreed: plug it all in and test (a meter is your good friend as long as you know just how to use it).

Best,

Doyle

[look 171]

Thanks again. If you have anymore tricks up your sleeves, please let me know. I will for sure try the test light trick. It is simple enough.

86 911 tagra, thanks for the link.

Jeff

[scarceller]

Originally Posted by look 171

Thanks again. If you have anymore tricks up your sleeves, please let me know. I will for sure try the test light trick. It is simple enough.

86 911 tagra, thanks for the link.

Jeff

When obtaining a known good Ground or 12V it is always best to get these right at the battery if you have a test lead that's long enough. I keep extra long (10') leads with alligator clips in my tool box for this purpose.