Packard Forum Index » V-8 (1955-56)

Instruments not working 55 400
Bought “used tested” voltage reducer. Tested it on a known working 56 system, worked ok. Mounted voltage reducer on 55. Turned power (aux). Temp gauge went to mid-range with the engine stone cold, fuel gauge at E with 15 gallons in the tank. Emptied and dropped tank. Removed sending unit with the feed wire attached, grounded sending unit., and moved the float up and down. Gauge responded correctly. Ensured wire covered with electrical tape, installed tank, Put 10 gallons in tank. Powered up, Gas gauge at E temp at mid-range. Engine cold.
I'm stuck! Any suggestions?
Happy

Wires crossed or shorting to ground, perhaps? The gauges ground through their sender units. Lower resistance = higher reading. An ancient wire with compromised insulation can short to ground and cause a high reading. Each gauge used individual wires held in place by nuts, so it's easy to get wires crossed between gauges. That would cause all kinds of funky stuff.

By the way, removing the instrument cluster from these cars SUCKS.

Please don't wrap wires with electrical tape. The adhesive melts into a gooey mess after a short period of time and the tape unravels, leaving the goo behind. Heat-shrinking is far better, as is wrapping the tape with non-adhesive vinyl wrapping tape also known as "plating tape". It's what the OEM's used. I get it from Grainger. Fraying cloth wires can by stabilized by painting them in several coats of liquid electrical tape. Basically, vinyl melted in solvent. It soaks into the cloth and dries into vinyl.

Is the oil gauge reading correctly. If so, along with the fuel gauge working properly when off the tank, would indicate the regulator may be OK. I would temporarily disconnect the wire from the temp sender and see if the needle drops to cold just to eliminate a bad sender as a possibility. It could be the terminal or even the wire somewhere is making a feeble connection to ground resulting in the half gauge reading. I would also suspect that since the fuel gauge and fuel sender worked properly when you had a good solid ground to the sender that there may be an issue with ground to the tank or the sender to the tank. Once a tank has been removed from the car it often does not for whatever reason make a good solid ground contact again. Many have resorted to adding a separate ground wire directly between the tank or sender and body sheet metal.

Update: Started engine ran up to normal operating temperature ( thermostat open). Oil pressure gauge working. Temperature gauge in normal (mid-range). Now only concern is gas gauge. Will cut hole in trunk rather dropping tank. Expect to solve problem!
Tank has copper wire ground to frame.
thank you all for the input!
Happy

If you are planning to keep the tank in place while cutting be careful of anything that could cause a spark. Gas fumes could accumulate if the sender gasket is iffy plus there is not a lot of room between the trunk floor and top of tank.

This gives me motivation to re-tackle the wacky gas gauge in my '55 Patrician. It now will show the correct fuel level but then bounce around in a semi rhythmic manner. Ground checks out good but I still wonder about the instrument voltage regulator. Hooked a voltmeter to it and got a bouncy reading on it too. With my body for now as it is more or less should be at 75 I want to give this gauge mystery one last shot.

I have added one new tool to the toolbox: A Cellphone; in case I need help getting out from under the damn dash!

Any ideas, as always, will be gratefully accepted!

Jim L in OR