Gas gauge/temp gauge not working after IVR mod-Need help!

New to the forum. Need help with gauge issues. Before mod gas and temp gauges
pegged to the right however once in a while would behave. Did the transistor & capacitor mod to replace old internal IVR (input to 12v on gauge, output to 5V on gauge, center to chassis ground). Now gauges barely move off left stop. Any ideas out there where I went wrong?
Thanks in advance for the help.
Willie Lee

if your gauges worked intermittently prior to mod - maybe you have an intermittent connection or wire first - the gauge pod if i remember, originally is grounded thru your mounts by the screws - when i did the mod i also ran a separate ground wire from the gauge assm to the body - i would check other wiring also - as far as the mod which procedure did you follow ? - if you used the solid state regulator ( not transistor ) - that is the 7805 - double check the wiring - do you have 12v to the input and around 5v at your output ? - oo3

Thanks oo3 for the response. Based on your advise I am going to start from scratch and recheck all of the wiring to the 2 problem instruments and recheck the wiring we did to the IVR which we built from the 7805 and the capacitor. It may be that the small wire to the winding inside is broken. I will also run new reliable ground wires to the dash. I will advise the result. Thanks again for the help!
Willie Lee

Another thing that could have happened, is that the instrument VR sounds like it was failing short, rather than failing open. This can put too much voltage through, cooking the gauges. I sure hope not, but after you have double-checked your work, ground the fuel gauge lead for a minute or less to see if it will read full.

which winding are you talking about - if you refer to the mechanical regulator winding i would just clip that out of circuit - if you are talking winding for gas gauge it is also possible like rod said it has overheated and windings have cooked - did you look at this - https://vintage-vans.forumotion.com/t1077-gauge-problems - oo3

I want to thank everyone who responded to my request for help. I can see that being a newbie to vintage Mopars will not be a lonely ordeal. There is a lot of helpful information in the members here and I do appreciate all of your input. I will tear into the dash this weekend and will post my progress here.Thanks again, you are a great bunch!

O.K. I did some prelim. checking last night and this is what I came up with:
Checked voltage @ homemade IVR, 12v in and 5v out at post to temp gauge
With sender wire removed from gauge showed 5v @ sender post to cluster body
Grounded sender post and needle move to full
Checked connections at battery and will move down the line towards the gauge

Where do I go next?
Thanks Willie Lee

So you have 5V at the gauge and if you ground the other post, the gauge swings to full. This has proved battery, circuit to the IVR, the IVR and the gauge. The issue is going to be the circuit from the gauge to the sending unit, the sending unit, or the ground at the sending unit.
The next step would be to ground the wire at the sending unit and watch the gauge. It should move the same as when you grounded the gauge.
The coolant circuit does have a resistance wire, so it may move slower. I'm rewiring my 108 engine sub-harness and will be measuring the resistance of the old wire. I will post what I find.

If it does not move, you have an open circuit between the gauge and the sending unit.
The sending unit can be bad. They usually fail open too.
The ground (the connection between the sending unit body and the head - the threads) is usually not the fault, unless badly corroded. Even sealer on the threads doesn't block some metal-to-metal contact, allowing the ground.
If you are working on the gas sending unit, the same stuff applies, but there is no resistance wire. Also, the ground is through the fuel line with the strap. You might think that there is a ground also through the face of the sending unit and the lock ring, but the tank usually has a pad on top and on the strap(s). Not a solid enough connection to the body for a consistent ground, especially with a fresh zinc coating. So they spent the money and time to put in that little strap to the fuel line. It's probably anti-static, too.

Rod,
Excellent information. That will be my quest this afternoon. I think I have isolated it to a grounding issue. I will also try running a new (cheater)wire to the gauge from the sender and see what the gauge does. Maybe time for a new sender. Thanks again.

So I grounded the wire at the sender and the gauge goes to full. I removed the ground strap from the fuel line , wire brushed all surfaces of the line and the clamp, re-attached it and still no luck. I think I have isolated it to the sending unit. Either the float sank or the winding is open. Should I order one off EBAY? Help mister wizard, help!

Ya gotta pull the sending unit out anyway, See what the problem is. Ive had a couple of these apart in the last couple years and some had bad floats. Either totally rotted and crumbly or pin holes in them. The sender can be checked with a Ohm meter.

here is a new one. http://www.ebay.com/itm/Mopar-64-65-66-Dodge-A-100-Truck-gas-fuel-sending-unit-/360454550571?pt=Vintage_Car_Truck_Parts_Accessories&fits=Make%3ADodge%7CModel%3AA100&hash=item53ecc3f42b&vxp=mtr

Sending unit on the way. I will advise what transpires. In the meantime now the heater core seems to be leaking. This truck is trying my patience!

Just as a followup on the resistance wire I mentioned earlier.
The wiring diagram shows a "resistance wire" between the 4 pin connector and the temperature sending unit. I measured the wire(s) and the connector. It seems there is a resistor built into the connector. There were 2 wires coming out of that part of the connector. The Black w/Red trace was a thin, single strand wire. There was also another typical multi-strand wire at the connector. Both showed 5 ohms from the pin to the wire.