Gauges and warning lights - anyone done this?

[Papa Whisky]

Morning all.

I am currently getting my late mother's '75 845 TL back on the road. The engine and box are out so I have great access to the wiring loom. It has the 2nd type dash.

I want to keep it looking as original as possible inside and under the bonnet, but I have a few ideas to make it reveal its secrets to the driver before it's too late...

I would like to:

1) turn the red oil pressure / overheat lamp into an ignition warning lamp (moderate)

2) turn the redundant amber heated-screen lamp (the HRW switch has its own intergral telltale lamp) into the oil pressure lamp (easy enough)

3) turn the voltmeter into a temp gauge using a transmitter in the water pump where the overheat switch is located. (Hmmm...)

The manuals I have (including the genuine Renault factory one) are to say the least very vague about how the voltmeter works. I'm sure that with a lot of trial and error I could get there, but I was wondering if anyone had any tips? Some tinkering with sender resistance might be required but I could wire in a small rheostat for initial setting, and set up using Infra red thermometer.

Any tips would be greatly appreciated!

Cheers

Paul

 

[angel]

The charge warning lamp is not that easy. You either need a remote voltage regulator with a provision for warning lamp, or a later alternator with the built-in regulator.
The heated rear screen lamp receives +12V when switch is turned on and grounds via the intrument cluster - its bulb holder is metal. The oil pressure / temp warning lamp uses an insulated bulb holder, a +12V supply (switched) and lights via the sensors grounding.
The voltmeter is a thermal unit, so you first have to use a voltage stabilizer like these on Smiths systems. But since these provide a voltage of about 10.5V, the instrument will record in the very low range. I guess a fuel gauge from a similar instument cluster could be made to fit on the voltmeter place; being a moving coil intrument it will then be easier for you to match a thermal sender to it, if you can actually find one that provides 0 Ohms of resistance at 120 deg.C

 

[Papa Whisky]

Many thanks Angel! I will see if I can rig something up on the "spare" car (same model and year) which I can use as a Guinea pig.
I was considering a voltage sensitive switching relay like some of the split charge systems have but wire to the closed side of the relay so it would break the feed to the bulb when the voltage increases. My paranoia about temperature comes from years of working on, and owning, Rover K-series vehicles, where one looks at the temp gauge almost as often as at the speedo!

Paul

 

[angel]

...and has to replace the head gasket as often as brake pads!

 

[Eccles60]

Many thanks Angel! I will see if I can rig something up on the "spare" car (same model and year) which I can use as a Guinea pig.
I was considering a voltage sensitive switching relay like some of the split charge systems have but wire to the closed side of the relay so it would break the feed to the bulb when the voltage increases. My paranoia about temperature comes from years of working on, and owning, Rover K-series vehicles, where one looks at the temp gauge almost as often as at the speedo!

Paul

The K meaning kettle perhaps? A friend of mine was product manager of the K series and Rover 200/400. They knew what to do but the accountants' cost cutting as well as careless assembly of the gasket with the long bolts (much more care was taken by craftsmen during its development), led to the well-documented problems. Apparently the Chinese K series has no such problems because they copied and fixed it. It's much easier to copy and improve than start with a blank sheet and no money. Rover spent less developing the MGF than Ford spent on the late '80s Fiesta facelift.