Ok guys, I need help here. This a total frame off resto, so most everything has been replaced, this thing runs like a champ, I'm really happy with it.

However, disconnected temp sending unit between plugs 1 and 3 on left side, to change and check plugs for color (they look great), and then, reconnected the single wire hook up to the sending unit. Then, no temp gauge reading at all!!!!

Now, keep in mind, this gauge has been working fine for the entire breakin procedure, and has been reading right where I was expecting it to read. (when engine fully warmed up, gauge reads at about 40% (which equates a little less than straight up on the gauge), that seems about normal for a 74)

Now it reads "zero". (actually below zero, in other words, no reading at all)

Checked contacts on sending unit and contacts on wire from wiring harness. Everything looks good.

So I need some hints as to where this problem is. I can't recall for sure, but I think the sending unit is brand new. (If not, it looks brand new based on my cleaning it up to "new" standards, or whatever I did in this total frame up resto.)

The gauge was working just fine a week or so ago, like I said, disconnected it to check plugs. So what in the heck is happening here?

I haven't touched the gauge cluster inside the car, and wire to sending unit from harness looks just fine, sending unit is either new or near new, and/or cleaned thoroughly, but do these sending units just, for no reason, crap out?

Any help would be immensely appreciated.

Tnx, Bill

 

Its not anything inside the car. Either you crushed the wire when you installed the engine.
I'm not saying how I know that
Or the terminal came off the wire when you pulled it off.
You can take a pin and shove it through the insulation If a multimeter check for continuity, if no meter hook a bulb up to it and a battery, does the same thing. Between the terminal and the wire somewhere downline.
It worked, you touched it, now it don't work.

 

did u check your fuses?

 

Have you tied the ground strap to the block yet?

 

That temp sensor is a thermistor which decreases resistance with increasing temp. So if you connect that wire to touch a ground (engine, frame) u should peg that gauge inside the cockpit hi - with ign on of course. Maybe u want to use a low resistor (1K ohm) in series to ground first so u don't ruin the gauge too. Now u replaced ur engine grounds to the frame like jbs75 said on rebuild didn't u? U should have a black battery cable connecting the engine block to the frame (my '74 is on the p-side mtr mount) and a black cable again connecting the frame to the batt neg (-).

If u need a new sensor only Lectric Limited sells the correct one for our '74s. I tried every auto parts store in town for this after PepBoys sold me a switch instead of a sensor (and yes my temp gauge never moved while i boiled over ). If u need gauge repair i have to recommend Corvette Instruments in Florida - great work and great price.
Hope this helps. cardo0

 

You guys were right. Was really quite simple. It's just that it was working fine ever since the engine was back in a few months ago.

Per CF guidance, I stuck a pin through the insulation about 4 inches downstream of the connector that attaches to the temp sending unit.

Did a voltmeter check with ign switch on. No voltage at the connector, yet at the pin, 12.4 volts!

I examined connector very carefully. No apparent cracks, or anything that would indicate a problem. Cut the wire, replaced with new connector, works perfectly.

Sometimes the simplest things can be the most troublesome to fine.

Tnx to all for your help.

Bill