Pulsating Voltage in Gauge Wires??

[Stephan D]

Trying to get the original temp and oil pressure gauges to work, I found a new problem.

The voltage in the gauge-wires are pulsating from 0 to 7 volts, this happens with the engine turned off as well.

Is this normal?

(If I short the gauge-wires to ground, the gauges goes to max, so they gauges are working.)

 

[Mike69cuda]

Yep, normal if you have the original IVR (Instrument Voltage Regulator). That is how they work. I have had at least two bad temp senders over tha last few years. The chineseium parts are crap. I am not entirely sure that I didn’t damage one by over tightening the nut on the wire. Check the sender with an ohmmeter before you install. Should read 70-80 ohms at room temp.

 

[RedFish]

Senders body needs a chassis ground path too. A lot of paint in threads, teflon tape, etc.. can interrupt that ground path.

 

[Stephan D]

Yep, normal if you have the original IVR (Instrument Voltage Regulator). That is how they work. I have had at least two bad temp senders over tha last few years. The chineseium parts are crap. I am not entirely sure that I didn’t damage one by over tightening the nut on the wire. Check the wire an ohmmeter before you install. Should read 70-80 ohms at room temp.

Thanks, now I learned something today as well!

I just have the new water temp sender to play with right now, trying to check the sender with an ohm-meter just shows an open circuit, both hot and cold, might be faulty then?

 

[Stephan D]

Senders body needs a chassis ground path too. A lot of paint in threads, teflon tape, etc.. can interrupt that ground path.

I think it has good chassis ground, showing approx 0,5 ohms between the outer(black) nut on the sensor and ground on the engine.

 

[Mike69cuda]

Thanks, now I learned something today as well!

I just have the new water temp sender to play with right now, trying to check the sender with an ohm-meter just shows an open circuit, both hot and cold, might be faulty then?

If it reads open from the terminal of the sender to the case of the sender it is bad. It should read about 70-80 ohms room temp, about 10-20 hot (engine warmed up).

So yours may be bad out of the box. Same thing happened to me.

 

[Mike69cuda]

You can boil a glass of water in the microwave and dunk it in there to test it hot with an ohmmeter.

 

[Mike69cuda]

I made this handy dandy little test box to troubleshoot gauges. It works on gas, oil & temp. You hook it up in place of the senders and it can simulate low, half scale & full scale on the gauges. I can loan it to you if you want. Fits in a small flat rate box. Just pm me your address.

 

[Stephan D]

I made this handy dandy little test box to troubleshoot gauges. It works on gas, oil & temp. You hook it up in place of the senders and it can simulate low, half scale & full scale on the gauges. I can loan it to you if you want. Fits in a small flat rate box. Just pm me your address.

View attachment 1715641528

I appreciate your help indeed...but sadly we are on opposite sides of the globe.

 

[67Dart273]

The idea of the original late 50's technology for the gauge regulator/ limiter is "duty cycle." It produces an on/ off pulse that is "something close" to 50% on and 50% off. This then divides the power about in half. The reason the gauges don't "show this" is because they are very heavily damped---they move slowly. The original IVR worked similar to a turn signal flasher---a heating coil wrapped around a bi-metal strip heats it up and it moves, breaking a contact, and then cools off and remakes contact

These were used by Ford, Mopar, and I guess AMC. I don't know about anybody else. I don't think GM ever used a similar system

First encounter I had was in about 1967, I had a '60 Ford Falcoon for awhile. One day the gauges both pegged. I think the Motor's Manual belonging to my Father held the answer LOL

 

[MoparMike1974]

Sometimes you can see the gauge needles pulsating if you look close enough.
The bi-metal strip flexes and makes/breaks a set of contacts to regulate voltage. Very crude but it worked good enough.
The major problem with this design is when the contacts stick....burns up your gauges.