Early temperature gauge sender issues, Early temperature gauge sender issues Options

[forrestkhaag]

I am having some issues with the installation of an early temperature gauge on a new (second) 200 degree sender and new taco plate on a 1.7FI original motor in my 1971. The sender has been replaced twice.

The wiring has been "hot wired" directly to the green lead behind the gauge to the sender lug. this to eliminate the old wiring harness as the problem...

The ground has been hot wired to the negative terminal of the battery. ibid

The light works in the gauge. There is juice to the three gauges / the clock works & the voltmeter works...

The gauge is startled awake when the ignition switch is turned on / but only movers to the right of the cold white tick-mark on the left side of the scale after the engine is fully warmed.

Then, out of nowhere, after a spirited run of 25 or so miles, the gauge is either teenager-dead-asleep on-the-couch or dancing wildly (can you say teenager) in slashing movements between hammered to the right or fully dead or sometimes.... and very rarely while driving at various RPM's reading what i hope to be a nice needle somewhere just south of the wide red band.

What gives?

the offer:

I will donate 50 bucks to the first informative responder, your favorite charity, or other suitable recipient if you have an exacting solution. This is baffling due to the short circuit testing that says the wire is not the problem. The gauge is fully rebuilt and tested and apparently is not the problem. And, the second identical sender showing the same craziness is redundant and seemingly not the problem.

Sidebar: The gauge was recently overhauled and bench tested to be spot on for resistance.. and when the sender lug is grounded to the frame, it needles to the far right side of the gauge - which i am told is the test for the gauge for resistance and functionality.

Maybe this is simply another 914 debacle which makes for a much more interesting experience than my 993 or 996C4S that required a dealer to resolve a burnt out light bulb in the cockpit...........

Your thoughts please

[914Sixer]

Is the wire to the taco plate NEW ? If not chances are the old one is going open with the engine vibration.

[904svo]

Just a WAG but check with a ohm meter and measure the resistance of the sender
unit on the taco plate with the wire disconnected. One side of the meter connected
to the sender connection the other side measure it to the engine case and then to the sender bass side. they should be the same. If the engine side is open or higher the taco plate is not grounded properly.