Gauge resistances?

[kacomess]

I am trying to determine the resistances for both the water temperature and the engine fuel level gauges for my 1995 D-90 (manual transmissions) in order to obtain correct generic (VDO) replacements (a cost-saving measure).

Thanks in advance,
KAC

[Terrys]

Man, I haven't done this in a long time. I used to build ham RF amplifiers and needed to do it, but it's been too many years, so I sure do hope if there's a EE out there who knows I'm wrong, say so:
This one of the occassions where a DVM works better than an analog VOM.
Take a known resistor whose value will be close to what you approximate the internal meter resistance. PPut in parrallel with the guage, and take a reading of the circuit. Take that reading, square it, subtract the square of the known resistance from that. Then take the square root of the remaining number, and you should get the meters internal resistance.

Whether I'm wrong or not, VDO are great replacements for the stock Def guages. FWIW, I used a VDO mechanical water temp guage, just because I trust them more. Did you know that behind that funky little finnisher panel where you square clock, cigar lighter and hazard switch are, are three holes, 2 1/8". You can get 3 matching VDO guages to go there, and LR parts manual for the defender (Wordlwide parts manual) has a 3 guage finsher panel. Looks good, and a good place for a Voltmeter, VDO round clock, Oil pressure (thats what I have in my 110) or whatever floats your boat.

[kacomess]

Thanks and...

a point of clarification. Will *any* VDO 3-point gauge fit and work properly in a manual-transmission D-90?

Second question: are those gauges significantly cheaper than Land Rover replacements (listed at RN for ~$200/gauge)?

Thanks,
KAC

[Terrys]

a point of clarification. Will *any* VDO 3-point gauge fit and work properly in a manual-transmission D-90?

Second question: are those gauges significantly cheaper than Land Rover replacements (listed at RN for ~$200/gauge)?

Thanks,
KAC

First off, the gauge doesn't care what transmission you have.
By *any" what do you mean? What do you want to monitor?
I'm not sure what you mean by 3-point, either. The oil pressure gauge is a 3 wire unit, one +, one -, and the third to the sender.
There are several styles, several sizes. You want the 2 1/8" diameter units. Yes, they are alot less expensive, and frankly a hell of a lot better than LR instruments. Also, you will be able to do away with the voltage stabilizer too. That was to bring the voltage down to 10.5 volts, and balance the fuel and water gauges. Without having ever changed my original fuel guage (though I may be on my 3rd sender) I'd be willing to try using the VDO fue gauge with the LR sender and see what happens. It can't be any less accurate than stock.

[kacomess]

clarification

Sorry to confuse the issue.

My basic question is this: Do you know exactly what VDO gauges I would need to order to replace the LR water temperature and fuel gauges?

The mechanic who's doing the work contends that VDO gauges have different resistances. Unless he orders the gauge with the same resistance as the LR gauges, they won't read correctly. He can't find out which gauge to order, so he's left that task to me. Hence, my obtuse questions.

One final point of clarification: both LR gauges work, but when the dashboard panel lights are on, water condenses behind the glass of the water temp and fuel gauges. Replacing the O-rings on these did not solve the problem. That's why I'm looking for replacements!

Thanks again!

keith

[Terrys]

NO, I don't know what gauge you want to use. VDO makes dozens of gauges, styles and sizes, not to mention mechanical, and electrical.

Tell your mechanic I think he's the one being 'obtuse'. Actually I think, since he's charging you to do work, he's an outright idiot. He "knows" the gauges have a different internal resistance, but doesn't know what the LR gauge resistance is? He must be clairvoyant. Give him the formula and tell him to do the math. Jeeesh!

Better yet, let me save you the trouble. Your water condensation problem is not because of your gauges. It's because it's a Defender. They all leak water to some degree, usually down the scuttle vents along the inside of the bulkhead. My VDO guages show condensation too. Two suggestions;
Live with it, and find a mechanic who isn't a prima donna.

[kacomess]

Thanks and...

I agree with your assessment on his attitude, but finding a competent mechanic near my house is a problematic venture.

As long as the condensation behind these two gauges won't damage them, I won't be too concerned. I had a 1971 Series II-A before I purchased this D-90 (it formerly belonged to Mark, here at RN), so I am quite accustomed to water problems. I just assumed that the issue with condensation behind these two gauges (new issue since last year) would eventually cause them to malfunction.

Thanks again,
Keith