64 Spyder Electrical Issues

[lonestranger]

After replacing Engine, Body and Dash harnesses in my 64 spyder convert (with new harnesses from Clarks/M & H Electrics) to address (among other things) a non-working cylinder head temp gauge issue and harnesses that had been "modified" by a stereo shop to install a am/fm stereo radio: first, I found that now, the previously working gas gauge also was not working (needle pegged full right -key on or key off)! And secondly, while checking to see if any leads/connectors were wrong/unplugged, I got a "small" spark at the fuel gauge and everything went DEAD! I checked the under dash fuses and all appear good. It acts like a car that has a blown fuseable link, but I see no mention of such a link on the wiring diagrams in the factory manuals. Any ideas or suggestions would be welcome and greatly appreciated!

PS; The cylinder head temp gauge still does not respond! I am going to change the thermistor next and see if it help.

[bbodie52]

Here is some material, including some theory on how the fuel gauge circuit functions. Hopefully this will help with your troubleshooting...

The attached wiring schematic shows the fuel gauge circuit on the 1964 Corvair. This is a very basic circuit, with power coming from the fuse block via a 20 Gauge B/P (Black with Pink Stripe) wire to a connector on the fuel gauge. You should be able to measure 12V DC at this connector with a multimeter (with the key ON) with the other multimeter lead grounded. The other fuel gauge connector is a 20 Gauge T (Tan) wire that is routed to the fuel tank sending unit. The sending unit must be properly grounded to function. When the tank is empty, the sending unit basically is at 0 ohms resistance, and full current flows through the gas gauge, giving an indication of Empty. As the fuel level rises, sending unit resistance increases, which reduces current flow and moves the needle toward Full. You should be able to ground the Tan wire at the fuel tank to obtain an Empty reading, and an open circuit (tank wire disconnected) should show a Full meter reading. Note that the gauge itself must also be properly grounded for the "F Coil" (as it is referred to in the description) to be properly energized to pull the needle to the F mark. If the ground connection on the instrument panel is faulty, the "F Coil" will not be energized properly, and the gauge will not function properly.

You should use a multimeter to verify the presence of 12V DC at the gauge input. The resistance (ohm) setting on the multimeter can be used to ensure that the gauge housing itself is properly grounded to the car chassis. You should also be able to measure 12V DC at the fuel tank wire, with the other test lead grounded. If the voltage is missing there, you may have a broken or loose wire between the gauge and the fuel tank sending unit. (All voltage checks are done with the key ON)

If the voltage is present where it should be (at the gauge input and at the fuel tank sending unit wire connector), and if you have a good chassis ground at the gauge housing and at the fuel tank sending unit, there is a possibility that the gauge itself has failed. If you determine that the gauge is faulty, you may be able to get a used fuel gauge on eBay.

The schematic wiring diagram and the written description below explains how the fuel gauge circuit functions.

Left-click each image with your mouse to enlarge the image...

1964 Corvair Instrument Panel and Body Wiring Diagram

1964 Corvair Fuel Gauge Circuit

1964 Corvair Interior Wiring Diagram

There is a 14 gauge B/P wire that feeds a central junction point in the wiring harness that provides power from the fuse block to many points under the dashboard. It is supported by a single fuse in the fuse block. If you popped that fuse "everything might go dead". I would trace that down and recheck the fuse block. Do the headlights, horn, fan, etc. work? If some things work and others don't, you should be able to analyze the schematic diagram for each device that does not work, and find out what is common to all of the non-working items.

The thermister can be expensive and difficult to find (used). It is a variable resistor. The wire from the thermister is not part of the main harness you replaced. It is a separate wire that is routed through the left sheet metal heater duct area. Replacing the main harness may not have corrected your thermister problem, if there is a fault in the separate wire. I would make some continuity and function tests with the harness and temperature guage before you blame the thermister, which may be difficult to obtain.

I have attached the appropriate section of the 1964 Corvair Shop Manual Supplement to help with your troubleshooting.

[lonestranger]

definitely appreciate the quick reply to my inquiry. Relative to your questions, everything is dead on the car - dash, lights, starter etc. That is why I said it acted like a car with a bad fuse-able link which can kill the electrical system function just like you have removed one of the battery cables. I will recheck all the wires for continuity. The fuel gauge stays past full whether the key is on or not. I know the tank is over 3/4 tank as I filled it just before I started changing the harnesses. I also have changed to a new "sub-harness for the cylinder head temp thermistor. I have bought two used thermistors that were supposed to be good, so I will change the unit out and see if it makes any difference.(After I fix whatever has "killed" the electrical system. The question I have is what is apt to be a focal point for the whole system, as this seems to be? Are you aware of a procedure to check the validity of the thermistor itself?

[terribleted]

There is a 12gauge red wire from the battery to the regulator and then continues as a 10 gauge red wire to the dash area where it fans out and supplies the ignition and rest of the car. A loose connection or damage anywhere along this wire will cause almost all your symptoms. Check for voltage along it and thru every plug, ill bet you find your total power loss.

[lonestranger]

Thank ya Ted - will be under it first thing in morning! Will give updates as the saga continues. Thanks again for the help and tips.

[lonestranger]

Update on the continuing saga of the FUBAR fuel gauge! First, I located the source of the mysterious loss of "electrical energy" in the whole system, that occurred upon my getting a "small" spark while looking under the dash for loose connection etc to fuel gauge. Turns out, apparently coincidentally, that the new engine harness connector came loose from the new body harness connector in the engine compartment! The multiplug does not have a lock to secure it, so after firmly reconnecting the two harnesses, I secured the connection with a HD tie-wrap! Energy restored!! However, the original problem still remains. Using the information furnished by two forum members (and my limited expertise with electricity) I checked for voltage in the "simple" circuit. I found that I have voltage coming into the gauge on the B/P wire, but no voltage going out of gauge to the tan (T) wire. Fuel gauge stays "pegged" past F, regardless of key on or off and whether mounted in dash or not. This would appear to be bad gauge Comments/advice most welcome. Incidentally, did not find any postings for spyder fuel gauge on EBay or Clarks.

PS: Haven't pursued the cylinder temp gauge issue further yet, as swamp has too many alligators at this time!

[bbodie52]

With no voltage coming out of the fuel gauge to route to the tank sending unit, the coil that pulls the needle to the Full side may be energized, but the other coil may be faulty.

A search on eBay shows three Spyder instrument panels with gauges, but no individual gauges. The cheapest is shown below with no bids and bidding starting at $100 with no reserve. You may want to monitor that unit and possibly purchase an entire Spyder panel.

ebay http://www.ebay.com/itm/Chevy-Corvair-T ... 35&vxp=mtr


Two other Spyder instrument panels are currently listed, but at significantly higher prices. My eBay search was "Corvair fuel gauge spyder".

Before you spend the money, be sure you double check the "bad" gauge. Shorting the Tan wire to ground should fully energize the "E" coil and pull the needle over to the Empty side. (simulating an empty tank with the sending unit at 0 ohms resistance).

You might also check with the Corvair Ranch in Gettysburg, PA. They sell many used Corvair parts and might have a used Spyder fuel gauge.


http://www.corvairranch.com/

[MBlaster1]

I have an extra dash with fuel gauge let me know if you want it.

[Tacozilla]

You may want to check the ground to your dash since you recently installed a new harness. If that is loose, it would cause the fuel gauge to peg full.