What's the difference between the "GAGE" and "COIL" terminals on the '39 Ford ignition switch? They both seem to get 12v with the ignition switch on.
Gage is hot “in”which should be from ammeter. Coil is just that, power to coil or coils when switched on.
So anything that needs switched power can run off the "coil" terminal... for example a relay that runs a solenoid for an overdrive? Thanks.
Check to see if there is continuity between the two terminals with the ignition switched off. On a lot of early switches [pre-Acc days] it was simply another post to connect to. [Tri-5 Chevy switches are exactly like that] If that was the case ,then the "Gauge" terminal would be HOT with the 12v Battery Most Ammeters are "In-Series" between the Battery and the ignition "Batt" terminal ,and the charging system is connected to the ignition switch side of the Ammeter [usually at the ammeter] again easy to check for continuity
Here is a Basic 39 Ford Schematic It shows the ignition on one terminal and fuel and oil pressure gauges on the other terminal And the ammeter between the battery and ignition [with the Gen between them] The cig lighter is constant 12v If you wanted to connect up any Accessories [radio] simply connect a small Fusebox "Bus" to the gauge terminal on the ignition switch
If using the original Ford switch, I would use a relay off of the gauge terminal to power accessories. Those switches are over 80 years old and warn out. I have seen them get very hot when used to power accessories through the switch.
That’s exactly what I did. I wanted to retain the factory switch but didn’t trust putting a lot of amps through it. So I mused used it to trigger my Coil/Acc/ and Fuel pump relays
There is no continuity between Gage and Coil on my switch when it's off. I currently have 3 things on each terminal...not even sure what they all are. The item I'm "worried" about is the relay that powers the solenoid on my OD unit. The COIL terminal feeds the relay that goes to a toggle that goes down to the solenoid on the OD. Is there any reason that wouldn't work...or could that cause problems? Thanks.
For those who don't know the stock Ford switch only has two positions: on and off. When the switch is on; the brush inside connects all three terminals. Earlier switches are similar; but only two terminals. Good idea to use the switch to trip a relay if controlling more than stock stuff.
Sounds good. Thanks to all. Thanks for clearing that up, Rich. The only thing that's new is the overdrive circuit which is going through a relay.
Not sure it’s useful to you, but on my 55 bird, I believe the o/d relay was fed direct off the battery, actually connected to the battery side of the starter solenoid. The relay coil circuit (light load) was fed off the ignition switch. The solenoid uses quite a bit of power on the “actuate” coil, but once in uses much less current on the “hold” coil. That’s done with contacts inside the solenoid. In your case, I’d follow the advice above about moving all the loads to a new relay.
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