Hotting up the gauges

[GB SISSON]

Now that I am getting the original 6 volt positive ground system on my '47 panel dialed in I have some questions about the instruments. As I mentioned before, the column drop ignition switch was missing and the 3 wires to it were dangling but intact with their loop ends. I installed a generic ignition switch with the bat and coil wires. As I understand it, the 3rd wire provides power to the gauges. When I touch that 3rd wire to power it arcs and sparks pretty bad. Looking under the dash, all wiring looks like brand new. No cracks or anything out of place. Is that normal? Right now the fuel tank sender wire is not connected and is taped up well, as is the oil pressure sender wire. I do have the temp sender wire hooked up, but it arced the same before I hooked it up. The ammeter is working properly. The battery is showing 6.3 volts. It doesn't seem like I should hook up the gauge wire to hot ignition because it seems like a dead short. What do I look for? Thanks.

[JSeery]

One of the wires may be shorted or on the back of the gauges shorted to the case. I believe that the insulators on the back of the gauges are just a waxed paper type of setup. Might start by disconnection the gauges from each other and checking them one at a time to see which gauge system is causing the problem. I would remove the bars that gang them together and start with a new test wire. Pick a gauge and start with just it connected.

Edit: From the wiring diagram, looks like the wire from the ignition switch first goes to the oil pressure switch, then a wire connects it to gas and temp gauges (which are connected with a strap). I would start by removing the wire between the oil press gauge and the other two and see what that does. Then test a wire to the other two without the oil pressure gauge connected, and so on.

[GB SISSON]

Thank you. I will get to this after work today. It doesn't take a lot of flexing to destroy those old wires so I need to work carefully. I have been quite successful preserving wiring with heat shrink tubing over the fabric where it is starting to come apart. Yes, I know I should buy a new harness, but not in the cards this year....

[JSeery]

I would just disconnect the original wires and use a piece of test wire. Then you won't be moving them around anymore than necessary.

[41ford1]

You may want to remove the instrument cluster and check it on the bench. You are less likely to burn up a wire harness that way. Most likely someone has mucked around back there before you. The areas that are likely to have shorts are the buss bar, the paper insulator that covers the back plate on each gauge and the heavy paper board spacer between the gauge body and the back plate. The paper insulator on the back of each gauge can become so brittle it will disintegrate from handling. Usually the the spacer between the gauge body and the mounting plate are deformed enough to allow one of the studs to short on the back plate.
You have a good diagram provided by JSeery. Follow his method of checking each gauge.

[morrisgauge]

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The King Seeley gauge post index can also warp and cause a fault to ground. If it is on the power side of the gauge, the gauge will not actuate. If on the sender post, the gauge will make a full sweep. You would be wise to take your ohm meter to the cluster on the bench. Post to Post on each gauge you should have approximately 12 ohms, no post should be common to ground. This obviously excludes the ammeter, which should be the inductive "loop" style.

www.morrisgauge.com

[GB SISSON]

Originally Posted by 41ford1

You may want to remove the instrument cluster and check it on the bench. You are less likely to burn up a wire harness that way. Most likely someone has mucked around back there before you. The areas that are likely to have shorts are the buss bar, the paper insulator that covers the back plate on each gauge and the heavy paper board spacer between the gauge body and the back plate. The paper insulator on the back of each gauge can become so brittle it will disintegrate from handling. Usually the the spacer between the gauge body and the mounting plate are deformed enough to allow one of the studs to short on the back plate.
You have a good diagram provided by JSeery. Follow his method of checking each gauge.

Thank you. Great information. I didn't get a chance to work on it tonight and will be on the mainland tomorrow, so looks like Wednesday before I can get to it. Doesn't look like anyone has ever touched it back there. This truck has been in a wrecking yard since 1966. It had been owned by a mining outfit before that. Very hard thing for an old man to work on in place.....

[JSeery]

"Very hard thing for an old man to work on in place."

Yep! That is a true statement.

[supereal]

With the exception of the ammeter (or voltmeter in the '40) all gauges are supplied with battery via the gauge post on the original switch. Then, the senders provide a varying ground, hopefully in proportion to the function being monitored. If someone put 12 volts to the gauges, it is very likely that the bimetal heaters were damaged.

[GB SISSON]

The wire to power the gauges was disconnected when I got it. When I first got it running I ran it on 12 volts, but never connected the gauges at that time. Looks like I have a formidable project ahead of me.

[morrisgauge]

Well, if you get the cluster out and want them tested real quick, feel free to send them in. The shipping from Washington is pretty negligible. Be sure to keep your original sending units. Our customers have found that the aftermarket units don't work well.

www.morrisgauge.com