[Ozzmann]

I have speedhut gauges installed, in my 69 GTO which have been great, however ever since I changed my ignition switch over to a new one, my gauges have a grounding problem. most evident on my fuel gauge which doesn't show the correct level most of the time. switch the ignition on and the step motors automatically reset and display the correct level, but then when you turn the key and wind over the motor, the gauge must loose it's earth connection and the needle goes straight to full position.
if the car cranks for more than a few seconds, you can watch the fuel gauge needle, jump up with each crank the engine makes.
I have swapped the ignition switch out and put my old one back in, and it did the same, I believe it must be a ground wire in the plug the connects to the ignition switch. I must have done something to it when first removing it. Does anybody know if such a wire exists in this plug, or any other idea's?

[TedRamAirII]

I dont know that set up. For sure there should be a ground wire for the gauges, or a printed circuit board. The ignition switch does not have a ground other than the hole it sits in. A wiring diagram would point everything out.

[Ozzmann]

Originally Posted by TedRamAirII

I dont know that set up. For sure there should be a ground wire for the gauges, or a printed circuit board. The ignition switch does not have a ground other than the hole it sits in. A wiring diagram would point everything out.

The gauges do have a ground themselves, but this problem only started when I installed the new ignition switch. this is the one half way down the steering column.
till then these gauges have worked flawless for the last 4/5 years. The problem only arises while cranking, once fired if the gauge reads incorrectly, I just switch off and restart the car, and most times it will then read correctly. Something's got to be the culprit in the ignition switch wiring?

[64speed]

I hate electrical gremlins. There is a guy around here that does nothing but electrical work on cars. His shop is huge, his house is bigger so he’s making a ton of money, and his wait time is thru the roof but when you get it back you know it’s right. I am gonna attempt to rewire my car from scratch but if I fail it will go to him

[TedRamAirII]

I would verify the battery to engine and battery to body grounds. Get a volt meter and connect 1 lead to the battery ground terminal and the other to the engine, crank it over and see what your voltage is. Anything over .5 volt is cause for concern. If that looks good, then check from the negative terminal to the body. https://www.autotechnician.org/start...plain-english/

[chiphead]

Recheck the schematic for the gauges. It seems like the gauges may be starved for power or not getting powered up in the right manner.

Stepper motor gauges require power to the electronics to run the motors, as well as power to the sense wires that go to the fuel tank, CTS, oil pressure sender, etc. If you totally lost ground to the gauges, it wouldn't work at all. Loose ground could make it reset or do strange things, but you mentioned the ignition switch. Check grounds go directly to engine block or battery negative. (dash sheetmetal isn't good enough).

That power has to be clean, and not subject to ignition coil pulses, etc. Make sure the dash is powered by a dedicated ACCY terminal. If no spare terminal, the ign switch can drive a relay that pulls power straight from the battery. Starter solenoid engagement or ignition coil pulses will reset the control electronics in the dash and it'll do wonky things. So if you're doubled up on the ignition circuit or the charging circuit, I'd change it.

I've got a wideband gauge in my car, and some of the relays make it malfunction. Every time I purge the nitrous, the freaking O2 meter resets. I had to put freewheel diodes on the relay coils to keep the noise spikes from resetting the gauge. You may find it's something similar.

[Ozzmann]

Originally Posted by chiphead

Recheck the schematic for the gauges. It seems like the gauges may be starved for power or not getting powered up in the right manner.

Stepper motor gauges require power to the electronics to run the motors, as well as power to the sense wires that go to the fuel tank, CTS, oil pressure sender, etc. If you totally lost ground to the gauges, it wouldn't work at all. Loose ground could make it reset or do strange things, but you mentioned the ignition switch. Check grounds go directly to engine block or battery negative. (dash sheetmetal isn't good enough).

That power has to be clean, and not subject to ignition coil pulses, etc. Make sure the dash is powered by a dedicated ACCY terminal. If no spare terminal, the ign switch can drive a relay that pulls power straight from the battery. Starter solenoid engagement or ignition coil pulses will reset the control electronics in the dash and it'll do wonky things. So if you're doubled up on the ignition circuit or the charging circuit, I'd change it.

I've got a wideband gauge in my car, and some of the relays make it malfunction. Every time I purge the nitrous, the freaking O2 meter resets. I had to put freewheel diodes on the relay coils to keep the noise spikes from resetting the gauge. You may find it's something similar.

Thanks for the info, I'll recheck everything, just wasn't in a hurry to get in that fantastic position under the dash, back's been playing up!

[HWYSTR455]

Yeah, it's power, ground, dash lighting, and sensor. Not much can go wrong. I would check your power source too, it may not get voltage while cranking.

Not sure, but if you over-throw the IGN switch, it's possible it won't contact accessories terminal in the switch. So maybe the switch just needs to be adjusted.

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