VDO Oil pressure gauge

[Skyedriver]

Dash has been out, wires pulled from spade connectors rather than connectors off terminals. All recrimped/soldered although wires extended a little.
Gauge no longer works, connected as I think it should be, the needle goes to maximum, disconnect the earth from the inverted "T" it's minimum.
Gauge knackered or a wiring problem. I seem to have continuity from one end to the other..
Any thoughts from the electronic wizards out there?
Thanks in advance.

[GreenV8S]

I can't visualise the 'inverted T'. Do you have three terminals (+, -, sensor)?

The symptoms suggest one of those is not connected. I can only suggest you check - is at battery -ve voltage, + is at battery +ve voltage, the sensor has battery +ve on the other side, sender input terminal is at the same voltage as the output terminal at the sender and you're getting a sensible resistance across the sender. Check the spec for yours but they're typically in the range 10 - 100 Ohms.

[Skyedriver]

Would connecting the live to the sensor terminal and the sensor wire to the live terminal blow something in the gauge or the pressure sensor?

[GreenV8S]

Unlikely to damage the sensor but could easily damage the gauge.

[Skyedriver]

That's what I thought.
New gauge required it would seem. Damn!

[Lotobear]

Is it for a Caterham - think I may have an old one somewhere when I upgraded to a mechanical one?

If I can find it you can have it for the postage

[Skyedriver]

Thanks Lotobear, it's actually a TVR 350i but the gauge appears the same as the one in my 1990 Caterham and a 1989 Lotus Excel. All 5 Bar VDO gauges.

I purchased a new one from Demon Tweeks, decided to bench test it first, took care to connect up the correct wires to the correct terminals (+ve & -ve, no sender obviously) and the new gauge read 5 Bar max. Don't understand that unless the new gauge is defunct.

[Lotobear]

Ah,.. I found the Caterham gauge as well!

Personally I would convert to capillary as I've never trusted electric gauges

PS: my 1995 Caterham (K series) gauge is 10 bar scale so would not have worked anyway.

Edited by Lotobear on Tuesday 7th September 16:44

[Skyedriver]

Lotobear, would you do me a favour please, connect up the positive and negative leads to a battery and see if the needle moves.
Thanks, on mine, inc the replacement, it goes all the way to maximum, can't believe that's correct.

[McVities]

I will check my gauges tonight.
I connected the wires up wrong to mine and got instant full read when voltage was applied.
Once I had put the wires on the correct terminals, it worked fine.

Off the top of my head, the inverted T with lines looks like it should be earth, but I think its actually for the sender.
There should be a '+', '-' and inverted T moulded on the back of the gauge.

Failing that, there should be a wiring diagram online to download.

[Skyedriver]

McVities said:

I will check my gauges tonight.
I connected the wires up wrong to mine and got instant full read when voltage was applied.
Once I had put the wires on the correct terminals, it worked fine.

Off the top of my head, the inverted T with lines looks like it should be earth, but I think its actually for the sender.
There should be a '+', '-' and inverted T moulded on the back of the gauge.

Failing that, there should be a wiring diagram online to download.

That would figure!
Having said, a fellow on the owners FB page sent a photo of his and the upside down T was the earth I think.
edit: thinking about it, the earth connection is obvious (to me) in that it is fixed to the bolt rather than isolated.

Edited by Skyedriver on Thursday 9th September 15:44