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Power for gauges?

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Littlebeefy

Power for gauges?

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?

LittleBeefy aka Chad

“Dot Doitall”: 1984 Bronco XLT
460 (C8VE), Edelbrock Pro-Flo 4, ZF5, NP205, D44HP solid axle, 4.56
urban assault vehicle

"Bebe": 2022 Bronco Badlands 2dr
2.7l, Sasquatch, Iconic Silver, Black Marine-grade interior, hard-top

"Celeste": 1979 Porsche 928
4.5l K-jet, 5-sp, S4/GTS brakes, LSD, Pasha interior

Gary Lewis

Re: Power for gauges?

Administrator

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

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

Littlebeefy

Re: Power for gauges?

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

Re: Power for gauges?

Administrator

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.

Gary, AKA "Gary fellow": Profile

Jesse3877

Re: Power for gauges?

Great answers Gary!

RedBull
1981 F100, 73' 351W, C6, 9" 3.00L

Gary Lewis

Re: Power for gauges?

Administrator

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

Gary, AKA "Gary fellow": Profile