Inoperative temp gauge on a 1986 V6, it stays at the far left position, so first I disconnected the connector...

Checked resistance on the sender terminal opposite of the cutout/notch (for the needle) it measures 3.5 to 4.1 ohms at 68 to 70 degrees F.

- Correct right?

Then put a jumper wire from the green wire (for the red light) to engine ground with the ignition on the red light illuminates.

- Correct right?

Now the other terminal, put a jumper wire from the green/yellow wire (for the needle) to engine ground with the ignition on the needle doesn't move.

- I believe this is NOT correct, the needle should peg right?

[This message has been edited by Skybax (edited 05-04-2021).]

Yes, the needle should peg full right. You can also tell if the gauge is working by turning on the ignition. It should rest on the bottom of the thermometer and move to the 100 mark when ignition is turned on.

You know your bulb circuit is good, so it may be that it's actually your gauge that's gone south.

Ok thanks, I will check the ignition-on needle movement and post back...

Also, I haven't done "wire switch fix" yet to prevent needle from pegging because I want to get it working first, and I don't think it was done before I owned it, which is probably why the gauge isn't working now!

With the key off the needle is sitting exactly at 100 and when I turn the ignition on the needle stays at 100... no movement whatsoever.

EDIT: I just realized I did that test with the connector disconnected, I'll go back downstairs and try it again with the connector connected...

[This message has been edited by Skybax (edited 05-04-2021).]

Same thing... with everything hooked up, gauge at 100 with key off and key on, no movement.

Side Note: Oil PSI gauge sometimes works and sometimes jumps around when engine running, so I purchased a new 1988 oil psi sender and connector but haven't installed yet. To rule out other gauge malfunction and/or bigger problem, what should the Fuel Gauge and Volt Gauge look like with the KEY OFF and KEY ON?

[This message has been edited by Skybax (edited 05-04-2021).]

Update: I found answer to my key on / key off question in archives...

quote what the gauge says with the key off - Fieros use an 'air core movement' for the gauges. That is instead of using an electromagnet against a spring, they use an electromagnet against an electromagnet. The gauge won't become inaccurate as it ages because of the natural tendency of springs to weaken over time. But with the key off, there is no electromagnet, and thus the needle may just sit where it was with the key of or might move and then stop. What the needle does with the key off has no meaning with an air core movement.

So back to my temp gauge not working, I assume since the gauge doesn't move with sender grounded and/or key on, next step is to bench test the gauge right?

Found this is archives...

quote Once you carefully remove it (temp gauge) test as follows. A member helped me troubleshoot it using the following instructions. “To check it you will need a 12-13V power supply and a resistor 130 to 140 ohms. Looking at the back of the gauge you have 4 posts. The top center post is ground, the left post is 12+ volts, and the right side post is the reading in ohms from the sensor on the engine block. You place the resistor (130-140 ohms) across the signal post to the ground post. Hook up + an - from the power supply and the gauge should read around the 220 to 230 degrees.” You can buy resistor kits on Amazon/eBay in various values. Then you attach them in series and add the values together to get the resistance you want. Now you can reference the table again and the gauge should indicate the temperature based on the amount of resistance you’ve put inline. Approximately anyways, within a couple of lines.

Is there anything else I can check or I'm forgetting before pulling the gauge? (really don't want to pull that gauge out, lol)