Hi All New here with Alt gauge problem

[Reamer]

I have been on the FTE site for many years and now and I just picked up a 1990 Ranger XLT, I hear this is the place to be!

It has the 4.0, Auto. All gauges work except the ALT.
Key off, Battery measures 12.7v
Engine running, Batt measures 14.7.
We know the alt is good, but is there a common issue to look for, or just start tracing....






Thanks

 

[RonD]

Welcome to TRS.

Clean truck

There isn't an "alternator gauge" anymore, an amp gauge, we lost them around 1985.

They all use Voltage gauges now, it is just tied to a Key on circuit and ground, no connection to alternator, but it would show key on engine off voltage, then it should be higher when engine is running.

And it will move when head lights are turned on and off.


It is powered by the dash wiring and if its the only gauge not working then gauge itself may be the issue, not a fuse.
Usually oil pressure gauge and volt meter share the same power/fuse

Also test battery voltage after driving around, but before you shut it off, should be down around 13.6v.
Constant voltage above 14v will shorten battery life, just after starting it is normal to see up to 14.9v but that should only last a few minutes.

 

[AllanD]

Ammeters are wired in series between the power source and the load...

They tell you the "trend" within the electrical system

a Voltmeter tells you status, where you are but both require some intelligence
to know what they are telling you and what that information needs...

Personally I don't consider an ammeter all that useful, mostly because I place my trust in the idea that everything in my truck turned on all at once simply cannot use ALL of my Alternators 130amp output...

That Includes my stereo and both amateur transmitters one draws 20amps and the other close to 40amps)

 

[jeremysdad]

Inarguably, a combination of voltmeter and ammeter would be best.

Prefer that the ammeter be underhood, due to risk of fire. In cab, take a voltmeter all day long.

Can we help this person? Such silliness detracts from the ability of Jim to convince the 'it that rules' to justify the server as a 'justifiable' expense.

Just saying.

 

[jeremysdad]

Beautiful truck, op. Nice score! Maybe jy cluster. Pretty sure they were all the same (tach excluded) 88-94, could be wrong. Take a picture and bring your phone when you go to the jy. The differences are obvious. One's rectangular, one isn't.

Good luck!

 

[Curious Hound]

IF I wanted to monitor amps, I would install a shunt resistor at the battery and use an appropriate volt meter/voltage sensing circuit to monitor the voltage drop across the shunt resistor. Running full-sized wire to put any kind of dash-mounted ammeter directly in series with the battery would be expensive, potentially dangerous, take a lot of space for the wiring, and would probably be a general PITA to install for anything more than about a 40amp system.

I'm not sure how they did it way back when ammeters were common in cars. I wasn't into auto stuff back then and haven't had to deal with it. A volt meter should be good enough - just learn what it is telling you depending on current system conditions.

 

[85_Ranger4x4]

Its for a '91 but should give you something to start with.

 

[RonD]

To have a properly working AMP gauge ALL the power for the vehicle needs to pass thru it, except for starter motor amps.

To limit possible fires, or complete melt down, a Shunt is the best method for a dash board amp meter.
Shunt work like the MAF sensor, MAF sensor only measures 10% of the air flowing into the engine, computer bases full air flow knowing MAF is only measuring 10%.

Shunt passes 99% of the power to the system, Amp gauge just reads that extra 1%, but is calibrated for that, so shows actual amps, based on that 1%.
This allows smaller gauge wiring thru the firewall to amp gauge and if amp gauge should fail you won't lose all power.

You basically just need to hook it to the B+ wire on the alternator.

Alternator(B+)---------shunt----------fuse/fusible link-------battery(+)

Amp gauge hooks to each side of shunt, so the amps flowing thru the shunt are measured.

Example here: http://www.therangerstation.com/tech_library/EDiagrams/files/diagram_charging_1983to1985_1.JPG

 

[85_Ranger4x4]

I would check wiring and try to get it to work how Ford had it wired rather than how Ford wired a truck 5 years older with a very different charging system.

 

[Reamer]

Thanks!! Got it working, The gauge itself was un-clipped from the PC board..
Pushed in the clips and it works.

 

[RonD]

Good work

Thanks for posting the fix

 

[jeremysdad]

Gotta love an easy (and free) fix!