Last night I put a solid state regulator on my instrument panel, and when I went to test it this morning, the gauges worked (very slowly though) when the engine was off or idling, but when I gave it gas, they'd cut out. This happened to anyone else before? I remember doing the conversion on my ex's Dart, but don't think I used a capacitor when I did that one, and it didn't have any issues. Could the cap be what's causing this weirdness here? Any ideas?

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'74 Duster w/ HEI ignition, beat to snot suspension, A904, 8.25" 3.55 SG rear, still being tuned up and gets 17 MPG

Know how they always build a better idiot? That's me

Doubt it, if anything the cap would help. Is this a consistent thing? Do the lights and switches still work when you step on the gas? What if you keep your foot on the gas and keep the rpms held high?

Yeah I drove it around just to see if it'd clear up, but it didn't change. I had the headlights on the whole time, but still, I can't be driving around at night with no working gauges
It was happening even when holding the engine at high RPM. Everything else works fine though.

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'74 Duster w/ HEI ignition, beat to snot suspension, A904, 8.25" 3.55 SG rear, still being tuned up and gets 17 MPG

Know how they always build a better idiot? That's me

That almost sounds like something mechanically linked to the gas pedal... wire get wrapped around it? Something flexing upon acceleration.

Swap the mechanical one back in and see.

Did you heat sink the regulator?

A mechanical regulator puts out +12V until it warms up; the solid state puts out +5V instantly, so the gauges will warm up slower initially- that's totally normal. I've thought about building a circuit to emulate the old regulator, it wouldn't be that hard.

I would look for a loose ground at the engine and/or a broken engine mount - if the input voltage goes too high, most electronic regulators' internal thermal limiting shut themselves down...

Yeah I had to remember that when I first turned it on, so the slow gauges didn't worry me at all. If you do up one of those circuits, be sure to post up instructions on it. I'd love to have a well working gauge cluster to last me until I can install all aftermarket gauges.

Edit, I double checked all my grounds and everything's okay. I'm going to do alot of work on strengthening my body and engine grounds sometime in the near future (got all the stuff, just gotta take the time to do it). I don't think it's getting too hot, since it's got the better heatsink (with Artic Silver thermal compound) on it. I'll hold a finger on it next time I test the system to see how hot it's getting.

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'74 Duster w/ HEI ignition, beat to snot suspension, A904, 8.25" 3.55 SG rear, still being tuned up and gets 17 MPG

Know how they always build a better idiot? That's me

How about replacing the 7805? They are a dime a dozen, maybe you have a flakey one.

I'm thinking you're right. I switched the poles on the capacitor, same problem. Removed the capacitor, same problem. Desoldered everything and put the mechanical regulator back in, gauges work perfectly. I ordered two regulators, but decided to just leave the mechanical one in until it dies or I have all my new gauges, whichever comes first.

It's possible I cooked the regulator myself too. I used silver-bearing solder and had my soldering iron (digital Radioshack one, pretty nice) set to 600 degrees. I kept contact time to a minimum, but still...

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'74 Duster w/ HEI ignition, beat to snot suspension, A904, 8.25" 3.55 SG rear, still being tuned up and gets 17 MPG

Know how they always build a better idiot? That's me

Can you measure the amp draw of the instruments?

I'm thinking you're drawing too much current for the 7805, and when you raise the speed above idle (and the supply voltage rises), the 7805 goes into thermal shutdown.

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes