Electrical question on digital water temp gage

I'm trying to install a digital water temp gauge in my 1919 Model T. The gauge works fine as long as the car is not running but as soon as I start the car it goes black. I do have an alternator system. The gauge is silmer to a Cobalt brand but a cheaper brand.( Which I'm starting to think this is the problem) My voltage with the car off is 13.48. With the car running its 14.85. I've tried running the power straight from the battery and also off my fuse block. Iv run the ground from the battery and I then tried running the ground to the block. Thinking that the problem may have been electrical noise from the coils I installed a electrical noise reducing capacitor from MSD but still did not help. Thinking that maybe it was getting to much amperage / power from the starter I installed a toggle switch to turn off the power to the gauge while starting the car and then turning back on after the car is running and still the same problem. I'm thinking that maybe the gauge is getting too much power/ amperage but I'm not smart enough to know how to reduce the amperage / voltage going to the gauge. So before I spend a bunch of money on an Auto Meter Cobalt brand gauge I want to make sure Iv covered all my bases on this one. Keep in mind that the electoral system in this car is of my own making. It's a modern fuse block with the power coming from the battery and all the lights and other wiring are now protected modern by fuses. Model T's did not have much of an electoral system to start with so if something should happen it would cook all the wiring in the system. Im stuck now, Not sure what else to do other than to either buy a new name brand meter or scrap the whole idea. I also tried installing an old school capillary / mechanical type gauge but the sending unit was too long to be installed into the gooseneck. What am I missing?

Does the polarity of the gauge match the polarity of the vehicle?

Try powering the gauge assembly off a separate 12 volt battery with the engine running. This will narrow down the culprit as either a noise conducted interference or as radiated interference. If it operates properly on a separate battery, then its a conducted interference problem and some filtering on the power leads may solve the problem using capacitors and possibly an inductor. If it doesn't operate properly interference may be entering the power leads. Using a braid around the power leads may also be a solution. The Cobalt brand you mentioned may be better because its a better design that shields the interference (conducted or radiated). Just my $.02 worth

I can guarantee that a properly maintained cooling system is more reliable than any gauge you can buy.

There's a shocking $0.02.

Bernie

Since a digital unit isn't current hungry you can use a Zener diode to power the unit. I'll assume that you unit is 12 volt so a 12 volt Zener is what you shoot for. I woulddo the checks as stated above to make sure RF interference and over voltage is not your problem. Just twisting your power leads can help as equal and opposite cancel but shielding with a ground are your best bet. Here's a pic of armored SST spiral wrap (look below the fuel filter). I get it from a company that installs garage doors.

Well, I tried everything, Even a differant battery and the damn thing went really nuts then. I unhooked it and tossed it in the garbage pail. After talking to the Auto Meter folks and telling them what I was doing they assured me there gauge would do the job, So got the new Auto Meter gauge on its way. Now that said I did order it off Amazon so if I do need to return it I can send it back with no questions asked, Even got it a couple of dollars lower through them for the same gauge. I will try and find the shielded wire and that Zener. Thanks everyone for the help.

That shielded wire could be a life saver when those boys at Fort Drum practice without a ground spotter.

Bernie

You will need to know what to do with a Zener diode if you decide to purchase one. It acts as a simple way to keep the voltage to your gauge from going over the voltage rating of the diode. You can buy Zener diodes in all kinds of voltages. Be sure to look up how one is used before you get it.

There is a good chance you have too much electrical noise from the spark plugs and wiring for the gauge to easily work in your application. Good luck!

Terry

Edited April 29, 2015 by TerryB (see edit history)

Problem solved, Scrapped the cheap gauge and went with Auto Gauge.

If I want to drive a car that old, Me personally, I want the old car experience. Give me an old time MotoMeter. Sensitive and modern electronic stuff has no place in an early auto. Dandy Dave!

Edited May 8, 2015 by Dandy Dave (see edit history)