motor senders, gauge stuff

[bagmaker]

Any guru's know about gauges?
1987 Volvo but fairly standard gauge senders for that vintage, etc.
I am re-doing the basic dash gauge wiring. I want to understand what is happening as half was never working and the half that was, well, I was a bit enthusiastic about weight loss

For a 2 wire oil pressure sender / gauge, does the dash send power it and measure the resistance or is full power sent to the sender and the dash measures the feedback?

For a tacho, there is a simple 2 wire sender counting teeth on a layshaft. Does the dash (gauge) send the power which then gets grounded or do I power the sender and the gauge counts the positive pulse feedback?

For a low water alarm set in the expansion tank (2 metal probes) I imagine power is running through them and the coolant acts as a switch. No coolant, no electrical flow. But this is reversed to a normal switch (lights up when ON, this would need to light a dash warning when there is NO coolant) so do I use a relay? But if I do this then I always have power running through the coolant? Perhaps thats why its a plastic tank......?

How do these work?
Any help appreciated

[T1 Terry]

The low water is a negative return, so one probe goes to the body work and the other back to the gauge/light. It should already be set up to only come on when there is no circuit through the water between the probes.
The oil pressure sender should also be a negative feed using the metal contact of the engine to one end of the resistor and the slide goes back to the gauge, full negative should result in a full gauge.
The counter for the tacho generally has a 5v supply from the gauge and it measures what comes back as a frequency.
You need a voltage stabiliser for the gauge positive supply so they don't change readings when you turn the lights on or flick with the indicators

T1 Terry

[BruceS]

Another job for you when you get home to Mannum Terry ....
I don't often travel at night but when I turn on the instrument lights all my gauges show a different value. (reading?)
I've thought it may need a thicker feed wire from battery.??

[Busman]

If you intend fitting a cruise control the voltage from the speedo will not be enough, we fed ours with 12 v to make it work.
Took weeks to work that one out !!!!

[jon_d]

It depends.

You're best with VDO or the good American gauges.

My tacho works on a hall sensor counting the pulse of the timing teeth.


This is how I calibrated it. Using a laser tacho on the lathe.

[bagmaker]

OK all, thanks for that.
Mr google was ever helpful too, for anyone searching in the future.

section-3-group-37-component-wiring-diagram-b10m-mk-ii-page-16-l-9d1da85af6a29133.jpg

cheers

[jon_d]

Hi Bagger,

this is what I have in the Bedford.... I could do with a voltmeter.

I find I pay most attention to the EGT and the revs

[BernieQ2]

The pic doesn't enlarge Jon . To small to see .
Bernie .

[jon_d]

i did for your small data allowance Bernie.

[BernieQ2]

Thanks Jon appreciated .
Bernie .