No power at temp gauge

[mlparkey]

With key on you should have battery voltage at the sending unit wire at the sending unit. If you ground the sending unit wire and the gage goes to full hot, then the wiring circuit is good. The sending unit controls the ground resistance. Full resistance, (cold), no resistance (hot). Sounds like the sending unit is not grounding.

 

[Tommy L]

They make two sending units. One for a idiot light and one for a gauge.
Right one?

 

[76burb]

With key on you should have battery voltage at the sending unit wire at the sending unit. If you ground the sending unit wire and the gage goes to full hot, then the wiring circuit is good. The sending unit controls the ground resistance. Full resistance, (cold), no resistance (hot). Sounds like the sending unit is not grounding.

How could there be a bad ground on the sending unit if it is threaded in the engine block?

What am I missing here?

I tested another new sending unit I bought(which other forums said is the only one that will work) and it had 530ohms resistance out of the box

 

[Snoots]

COOLANT TEMPERATURE GAUGE PARAMETERS

For Truck Years: 1967 - 1973
The Temp Gauge Needle Should Point to:
Left Line (Cold) when sender resistance = 350 Ω
Middle Line when sender resistance = 76 Ω
Right Line (Hot) when sender resistance = 51 Ω

For Truck Years: 1974 - 1978
The Temp Gauge Needle Should Point to:
Left Line (Cold) when sender resistance = 350 Ω
Middle Line when sender resistance = 68 Ω
Right Line (Hot) when sender resistance = 46 Ω

For Truck Years: 1979 - 1990
The Temp Gauge Needle Should Point to:
Left Line (Cold) when sender resistance = 1,365 Ω
Middle Line when sender resistance = 96 Ω
Right Line (Hot) when sender resistance = 55 Ω

As you can see there are three different ohm ranges
depending on the year. there are also 1/2" and 3/8" pipe
threads so you need to match the size.

 

[76burb]

COOLANT TEMPERATURE GAUGE PARAMETERS

For Truck Years: 1967 - 1973
The Temp Gauge Needle Should Point to:
Left Line (Cold) when sender resistance = 350 Ω
Middle Line when sender resistance = 76 Ω
Right Line (Hot) when sender resistance = 51 Ω

For Truck Years: 1974 - 1978
The Temp Gauge Needle Should Point to:
Left Line (Cold) when sender resistance = 350 Ω
Middle Line when sender resistance = 68 Ω
Right Line (Hot) when sender resistance = 46 Ω

For Truck Years: 1979 - 1990
The Temp Gauge Needle Should Point to:
Left Line (Cold) when sender resistance = 1,365 Ω
Middle Line when sender resistance = 96 Ω
Right Line (Hot) when sender resistance = 55 Ω

As you can see there are three different ohm ranges
depending on the year. there are also 1/2" and 3/8" pipe
threads so you need to match the size.

Yes ive seen all these numbers. But every sensor ive tested out of the box has like 6-800 ohms resistance lying flat on a table. Does that resistance change when it's screwed into the block? and all of the ones ive tried screw in to the engine correctly so threading isn't an issue

 

[Snoots]

To answer your question, no.
There is, or should be, a ground block at the left-upper kick panel behind the parking brake. Several dash grounds are attached there. The block itself has a tendancy to lose contack with the body.
I'd suggest that you remove the block, clean all of the contacts, re-install and try again.

 

[76burb]

To answer your question, no.
There is, or should be, a ground block at the left-upper kick panel behind the parking brake. Several dash grounds are attached there. The block itself has a tendancy to lose contack with the body.
I'd suggest that you remove the block, clean all of the contacts, re-install and try again.

behind the parking break is the fuse box. I did find 2 grounds attached to the metal bracket at top of the parking brake. Cleaned them and reinstalled still no change

 

[Ricko1966]

If you ground the sensor wire and the gauge swings and you remove it and it swings and you hook it to the sensor and it's dead. Then either the sender is dead or wrong,or it's not seating metal to metal for sensor ground to the head. That's it. There is no other possibility

 

[76burb]

Well it seems the problem is that there was no thermostat installed and once I installed a 195 thermostat the gauge works and sits just left of the middle line once the engine warms up.

 

[Snoots]

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