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  #1  
Old April 1st, 2012, 11:08 PM
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Ian Gregory
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ANother strange gauge question?

Had a problem with my temp gauge in my 97 since Iíve had the truck. Stock gauge works fine. Turn on lights, gauge rises, turn off lights gauge drops back to normal. Turn on ac, same deal. Turn on lights AND ac, gauge almost pegs. Other large electrical loads like the cig lighter, wipers, etc. do the same thing.

Actual truck temp checks out fine with a laser thermometer.

Easy fix methinks. New VDO gauge and sender, check. Run new 14 ga wire direct from new sender back to gauge, check. Run new 14 ga ground direct from gauge to a good solid ground point that is also tied to the battery, check. No fix. Same problem????

Anybody got any other ideas?

Thx

Ian
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  #2  
Old April 1st, 2012, 11:21 PM
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Chris Solis
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Sorry no help but I feel your pain, I've been round and round no joy. It sucks. The only thing I just found out is that despite checking and cleaning grounds and adding a ground strap and running all new wires my sender is still not grounded (the sender spade still causes the test light to come on when checking). So if you figure anything out please let me know.
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Old April 2nd, 2012, 01:33 AM
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Ian Gregory
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Thx Chris. Saw you're thread and your issues was/is REALLY odd.

Was sure mine was related to the stock sender and/or ground wires just being too small but it seems not to be the case. Only wire I haven't changed is the + feed wire but I don't see how that can be the cause?

Behaves the same with the stock gauge and the VDO. Same with the stock sender and the new VDO one.

Strange.

Ian
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Old April 2nd, 2012, 04:14 AM
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Was thinking more on yours Chris as I was considering my issue. Have you tried running a ground jumper to some point on whatever your sender is screwed into? Can't remember the setup in a TDi but you might not be getting a clean ground path between the engine parts and the block where your frame gound is attached possibly?

Thinking to bridge the inlet manifold to the block on mine to make sure I have a good ground path. I know the bolts should ground the manifold to the heads and the heads to the block despite the gaskets but is it possible that yours isn't? Have you tested the resistence of the ground at the housing that the sender is screwed into?
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Old April 4th, 2012, 02:45 PM
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Ian,

I was having the same problem with my VDO temperature gauge. There were a couple of problems that contributed to it. First, make sure that your gauge light circuit is separate from your gauge circuit:

- All ground wires for instrument lighting only goes to instrument lighting
- All ground wires for gauges only go to gauges
- All supply wires for instrument lighting only goes to instrument lighting
- All supply wires for gauges only go to gauges

You can check this by removing all gauge and lighting connectors, unplugging the instrument cluster at the main connector, and performing a continuity test at the main instrument cluster plug for the four pins:

- Instrument lighting ground
- Instrument lighting supply
- Gauge ground
- Gauge supply

No pin should be in contact with any other pin. I had crossed them over at a couple of points, once for a ground and once for supply.

I also added an additional chassis ground to the instrument ground circuit. Probably not needed once I sorted out the above, but given I've added a tach, I figure an extra ground couldn't hurt.

Good luck.
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Old April 4th, 2012, 08:02 PM
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Quote:
Originally Posted by michael67 View Post
Ian,

I was having the same problem with my VDO temperature gauge. There were a couple of problems that contributed to it. First, make sure that your gauge light circuit is separate from your gauge circuit:

- All ground wires for instrument lighting only goes to instrument lighting
- All ground wires for gauges only go to gauges
- All supply wires for instrument lighting only goes to instrument lighting
- All supply wires for gauges only go to gauges

You can check this by removing all gauge and lighting connectors, unplugging the instrument cluster at the main connector, and performing a continuity test at the main instrument cluster plug for the four pins:

- Instrument lighting ground
- Instrument lighting supply
- Gauge ground
- Gauge supply

No pin should be in contact with any other pin. I had crossed them over at a couple of points, once for a ground and once for supply.

I also added an additional chassis ground to the instrument ground circuit. Probably not needed once I sorted out the above, but given I've added a tach, I figure an extra ground couldn't hurt.

Good luck.
Thanks Michael,

Some good ideas and stuff to check there. I also plan to check my supply side to make sure it isn't a voltage drop issue from a weak alternator maybe.

Looks like the meter and the test probe are coming out and I have some checkin' to do.

Ian
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Old April 4th, 2012, 11:08 PM
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I have run a jumper cable from the neg terminal to the sender housing and still no reading on the gauge but I didn't check with the test light if it was grounded. Hopefully sat I'll be checking grounds starting at the battery with the test light and then working my way out following the ground straps and checking for the light to come on. As soon as I find a place that isn't grounded I'll fix it as see what happens. I will be checking again with the jumper to start. I'll def let you know
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Old April 7th, 2012, 03:03 AM
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Michael White
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I just remembered - I replaced my main ground cable too. Again, replacing the ground alone didn't fix it, but given the poor condition of the cable, it certainly didn't hurt.
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  #9  
Old April 8th, 2012, 10:03 PM
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Ian Gregory
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Fixed.

Re-checked the battery to frame/t-case and frame to engine grounds. No issues. Wires look OK and the connections where clean and tight.

Before I decided to dive in with a meter and start measuring and messing I decided to try something. Had an old ground cable for a winch that was too short for a defender. Decided to run it from one of the studs on the back of the driver's side head to the battery direct.

Ran it in, started the truck and let her warm up to normal temps. Gauge worked fine. Added loads one at a time until everything in the truck was switched on. Gauge never varied. Turned them all off and played around with different loads and so on. Gauge was rock steady.

So I am guessing itís just another case of Lucas undersized wiring degrading with age to beyond the capability of handling the design load. My winch cable is twice the size of the stock main ground!!

Probably not going to help you much with your problem Chris, sorry. Thx for the help and suggestions Michael.

Ian
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Old April 8th, 2012, 10:29 PM
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Hey I'll give it a shot since I don't have any other options.
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