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Topic: Alternator putting out 18 volts ??? 85 Tbird (Read 2389 times) previous topic - next topic

Alternator putting out 18 volts ??? 85 Tbird

I have an 85 30th anniversary Thunderbird thats been giving me some trouble.

A couple weeks back my dash starting reading 18 volts on the digital gauge. This was verified with a multimeter at that battery.

To keep the story short I've since replaced the alternator, voltage regulator and battery.
I had a friend bring over his fluke multimeter and test the VR wiring he said everything looks good. Issue is still present.

At this point I dont even know what to look at next. Anyone have any insight on this?

Alternator putting out 18 volts ??? 85 Tbird

Reply #1 –
For some reason the voltage regulator is not doing its' job.

The alternator output goes to the A pin of the regulator. The regulator keeps the voltage it senses on pin A at 14.5 volts by controlling the alternator output.

The regulator controls the alternator output by pulsing the alternator field current. Pin F on the Reg to terminal F on the Alt.

Try to measure the voltage at pin A of the Reg.
Make sure the ground for the regulator is not corroded.

Try measuring for voltage between the negative battery post and ground near the regulator. It should be zero or close to zero. If you have a voltage, check your negative battery cable grounds.

Alternator putting out 18 volts ??? 85 Tbird

Reply #2 –
yeah, its going to end up being the regulator.  its mounting is prob the issue.  I opened one up one day and found the internal ground run to be corroded.  Your's is new but make sure the canister has continuity to the ground pin on the regulator. The canister is what is bolted to the car so if its not bonded to the internal ground lead, i suppose it could be bonded externally.

Alternator putting out 18 volts ??? 85 Tbird

Reply #3 –
Quote from: jcassity;321115
yeah, its going to end up being the regulator.  its mounting is prob the issue.  I opened one up one day and found the internal ground run to be corroded.  Your's is new but make sure the canister has continuity to the ground pin on the regulator. The canister is what is bolted to the car so if its not bonded to the internal ground lead, i suppose it could be bonded externally.

Quote from: softtouch;321020
For some reason the voltage regulator is not doing its' job.

The alternator output goes to the A pin of the regulator. The regulator keeps the voltage it senses on pin A at 14.5 volts by controlling the alternator output.

The regulator controls the alternator output by pulsing the alternator field current. Pin F on the Reg to terminal F on the Alt.

Try to measure the voltage at pin A of the Reg.
Make sure the ground for the regulator is not corroded.

Try measuring for voltage between the negative battery post and ground near the regulator. It should be zero or close to zero. If you have a voltage, check your negative battery cable grounds.




Thanks guys, finally gonna dig back into it tonight.

One thing I'm a bit confused about. Is there supposed to be a ground wire for the VR? or is it just supposed to ground itself on the fender wall?

If there is supposed to be a separate ground it isnt there and wasn't when I got the car. I have tried grounding the VR case temporarily with no luck.

Alternator putting out 18 volts ??? 85 Tbird

Reply #4 –
the bolts that pass through the case and into the vehicle chassis will provide your VR chassis ground.

Granted, the internal ground on the circuitry is bonded to the case.

what you should do is use a meter and see if you have zero ohms or continuity from the VR chassis to the chassis of the car.

or......
connect test light up to pos battery then probe the case of the VR
-if light comes on but is dim, clean mounting surface of VR as well as bolt head / threads.

-if light comes on bright, you have a good chassis ground to the case of the VR, this tells us nothing about the internals of the VR grounding being bonded to the case.

You could easily find your chassis ground wire of the VR by measuring continuity from all the output conductors (one at a time) to the case of the VR.(granted the car is off and nothing hooked to the VR)

Alternator putting out 18 volts ??? 85 Tbird

Reply #5 –
Quote from: jcassity;322412
the bolts that pass through the case and into the vehicle chassis will provide your VR chassis ground.

Granted, the internal ground on the circuitry is bonded to the case.

what you should do is use a meter and see if you have zero ohms or continuity from the VR chassis to the chassis of the car.

or......
connect test light up to pos battery then probe the case of the VR
-if light comes on but is dim, clean mounting surface of VR as well as bolt head / threads.

-if light comes on bright, you have a good chassis ground to the case of the VR, this tells us nothing about the internals of the VR grounding being bonded to the case.

You could easily find your chassis ground wire of the VR by measuring continuity from all the output conductors (one at a time) to the case of the VR.(granted the car is off and nothing hooked to the VR)

Ground is definitely good, swapped VR again no change.

 My test light lights up red for B+ and green for - and makes an audible sound for both.

Well for some reason when I probed the "I" wire on the VR plug it lights up and I get no sound from my light. Everything else I have checked gives off the light and sound.

This is the wire that runs to my instrument cluster correct? Could it be shorting out somewhere and causing this problem?

Alternator putting out 18 volts ??? 85 Tbird

Reply #6 –
Problem fixed, thanks for all the help.


In the end I feel like a moron and fixed it for free....

Alternator putting out 18 volts ??? 85 Tbird

Reply #7 –
So , what was it ?
Fox-less at the moment
 

Alternator putting out 18 volts ??? 85 Tbird

Reply #8 –
Quote from: hypostang;322794
So , what was it ?


The stator wire was plugged in to the ground bolt on the alt.  :mad:

Again I feel like a moron but I never messed with it before this issue came up. How it got like that I don't know. I sure as hell didn't put 400 miles on it like that.