Power for gauges?

[Littlebeefy]

I’m replacing my gauges and I’m pulling the wires from the C-208 connection that plugs into the printed circuit board on the back of the OEM instrument cluster. I’ve mapped all of the wires and I’m a little confused about where to pull switched power from. The ammeter in the dash connects to the Red-Orange wire and the Yellow-Light Green wire. Is one of those switched power? Or is it the Dark Green-Light Green wire that leads to the instrument cluster voltage regulator?

[Gary Lewis]

Check your pinouts with Ford’s on the page at Documentation/Electrical/Gauges. And switched power in in Ckt 640, the R/Y wire.

[Littlebeefy]

Gary,
Thank you. When I looked at the schematics it seemed like the 640 R-Y wire was for the warning buzzer, but I now see that was the splice. So I can pull switched power from that. Will it give me power during starting or only when the key is in the run position?

Just for my own education, can you explain the ammeter hookups to me and why they aren't a good source of power? It seems like there are two connections to the ammeter that go back to the starter relay (I assume one is for "run" power and one is for "start" power?). Is the wire gauge for the ammeter the issue?

[Gary Lewis]

Chad - On the page below in the upper right corner you can see the R/Y wire for Ckt 640 and it says "Hot In Start Or Run".



And on the page below you can see the ammeter circuitry.  Basically the ammeter sits between the battery on the left and the alternator/cab circuits on the right.  If the alternator is supplying power to the battery that power will flow across the "shunt", and since the shunt is a fairly small wire a voltage drop proportional to the current will be developed, and that will show up on the ammeter.  Power to the battery causes it to show Charge, and power from the battery causes it to show Discharge.

Technically you can use either of those wires for power, but I wouldn't.  They are not intended for that and aren't fused, so if you cause a short you are going to burn up the wiring.  And they are hot at all times.

[Jesse3877]

Great answers Gary!

[Gary Lewis]

Thanks.  Let's see if they work for Chad.