VDO Vision 240-33Ohm gauge

[eherlihy]

OK. Uncle...

I bought a VDO 301-105 Fuel gauge for my O'day 35. This is described as a 240-33 Ohm Fuel Gauge. The fuel gauge in the tank works great, except that you can't see it.


This is a Mohler mechanical gauge that has the sending capsule built in. When empty it reads 247 Ohms, and when full, it reads 35. - Close enuf... I connected it as follows: +12V to the Instrument circuit breaker (RED), Sender "S" (PINK) to the sender, and a YELLOW wire from the other side of the sender to the ground bus. Simple eh?
Well the needle is PEGGED FULL 100% of the time.

OK, so I suspected the sender might be doing something unseemly, so I purchased a new sender, and crawled into the lazerette, and installed while practicing my yoga positions... same thing.. FULL 100% of the time.

So, I pulled the sender and tested it by moving the arm up and down. Still, FULL 100% of the time.

I then pulled the gauge and tried an ohm meter on the terminals. All the way up (full) read 30 Ohms, and all the way down (empty) read 246 Ohms...

Must be a bad gauge, I figured.. So I bought another new one. SAME RESULT!!!

ideas?

[tommays]

The guage will read full if the sender wire is grounded



Normaly the gauges would get power from a purple wire And the sender wire goes to well the sender And the tank would already be bonded to the filler and ground like the green wires in your picture

I would try and lose the yellow and see what happens

For reasons only they know even with your tests they do build senders and gauges in 10-180 and 240-30 and 30-240

[eherlihy]

Originally Posted by tommays

The guage will read full if the sender wire is grounded

yes, this gauge reads full if the sender (PINK) wire is grounded, or if it has 240 Ohms or 30 Ohms between the gauge and ground.

Originally Posted by tommays

Normaly the gauges would get power from a purple wire And the sender wire goes to well the sender And the tank would already be bonded to the filler and ground like the green wires in your picture.

I thought so too... It was after a phone cal with VDO support that I ran a separate (YELLOW) ground wire to the DC return, or "-" bus.

It's a short run from the breaker panel to the gauge. I used a RED wire to supply +12V to the lamp for the gauge, and jumpered that to the gauge itself.
Light on = Gauge on, Light off = Gauge off

Originally Posted by tommays

I would try and lose the yellow and see what happens

See above...

Originally Posted by tommays

For reasons only they know even with your tests they do build senders and gauges in 10-180 and 240-30 and 30-240

I've even addressed that... The Teleflex sender that I bought to replace the Moller has a thick-film varistor mounted in a piece of plastic which you mount to the U channel that drops in the tank. You can mount it so that it reads 240 Ohms (Full) to 30 Ohms (Empty), or flip it, and it will read 30 Ohms (Full) to 240 Ohms (Empty). No difference - it ALWAYS reads Full when it has +12 Volts applied to the + lead of the gauge, and goes to ground through either 240 Ohms or 30 Ohms.

Maybe - if I try connecting +12V to the sender, and run it to ground through the gauge it will work?

[tommays]

Maybe - if I try connecting +12V to the sender, and run it to ground through the gauge it will work?

That would be REAL BAD

Something is wrong we are still just not aware of what that is

[eherlihy]

I believe that I found the real issue...

While the sender was grounded, and the lamp in the gauge was grounded, the gauge itself was NOT properly grounded.

The CORRECT way is to have +12, a ground, and a sender wire connected to the gauge, and a sender wire and a ground at the sender.