bench testing instrument voltage regulator

[Teal68]

Anybody know how to bench test an instrument voltage regulator? ground to the body of it, but which connect does positive go to??? If it matters it's actually for a 69 Mustang

 

[DirtDonk]

They're usually marked with a "+" sign or at least the ones I've seen had it.
If not marked, many Fords use the male connector as the input and the female as the output to the gauges. This is standard safety procedure so that on the chassis wire side, it's harder for the connector to short out on metal if it's disconnected.
If you have the Mustang (or just it's harness) handy you can verify that part for yourself with regard to how that specific vehicle is wired.

To connect:
Ground to the case.
12v to the (correct) terminal.
Measure output at the other terminal.

If this is a stock type the output will be a "pulsing" signal. Oscillating between something like 3v and 7v to average out at 5v. I always thought it was 6v so that's what I put mine to when I adjusted it after the gauges started reading low.
If you have an aftermarket integrated-circuit type, it's a steady output so you can measure it with any volt-meter. I would still shoot for 5v-6v initially.

If you're checking an original, it does help to have an old fashioned analog meter with a needle you can watch. The new digital multi-meters can "see" the changes, but depending on the meter itself might not register it consistently on your digital readout. Sometimes you just see the voltage hopping all over the place.

Good luck. Let us know what you find.

Paul

 

[Teal68]

Thanks Paul, as usual! That was very helpful...ivr is good so on to the next steps.

 

[DirtDonk]

Great. One less part to buy!
Were the gauges not cooperating? Or are you just checking things before putting it back together?

Paul

 

[Teal68]

Paul,
None of the gauges were working. When I bought it did come with a new "circuit board" to go on the back of the cluster. You'll know what I mean if you are familiar with 69 and 70 Mustangs. While I had it all apart I wanted to check the voltage regulator because there's quite a few steps to getting to the cluster to be honest, and it can't be tested in place. Or at least I couldn't figure out how to.

So while I had it apart I checked the IVR, put the new "circuit board" on, and I also checked the power supply and ground for the IVR at the cluster clip. Oh, I also check each individual gauge. I even go the clock working too! All checked out so I put it all together last night and early this morning.

Guess what....no gauges and the clock is intermittent! The clock does not bother me too much. I can fine tune that I'm sure. The gauges...that puzzles me! I'm only getting like .3 volts at each sender (fuel, oil, and temp). Got some figuring out to do.

Sorry for the long answer Paul, but I always appreciate your thoughts and input.

Thanks,
Tyler

 

[DirtDonk]

Hey, don't talk to me about long answers!

And yep, I know about the old circuit boards. Great idea in fact for the day. But they do tend to not "age" very well. The truck guys hate them too. So many have deteriorated.
If you're only getting that little voltage at the sender then either the gauges themselves, or the wires and connectors between them and the cluster are to blame.
You're measuring that voltage at the wire though, and not the output of the sending units, correct?

I would think you should at least consider the clock related though. If it worked out of the vehicle and not in, something is wrong in-between.
What about the power to the cluster and IVR?

Paul

 

[Teal68]

Yes sir, I removed the wires from the senders and checked the voltage of the actual wire. That was after directly ground each wire just to see if they would peg out.

I checked the power to the clip for the IVR and it was good.

The clock has good voltage it's the contact points that need a little more work. Any advice on that? Would it be a good idea to put a little dielectric grease on the contacts???




Thought this was interesting...Something different about the Mustang compared to Broncos of the same vintage the fuel sender has no ground wire. It's ground thru the sender and tank. I check it and it ohmed out good.

 

[DirtDonk]

That is interesting. I guess they figure that the grounding characteristics of the tank and it's surrounding mounting points will always be good enough.
And apparently they're right so far if yours still works after 50 years or so!

...Would it be a good idea to put a little dielectric grease on the contacts???

I would say yes. The old metal contacts are not as corrosion resistant as modern or a newly minted old one would be. And if any oxidation has already taken a foothold, even if it's scraped off to a point, I would think it's just going to corrode again sooner than we'd like.
So dielectric grease on contacts sounds like a good idea to me.

Hopefully if there is a negative side to doing that someone will pipe in with that info. I know there have been several discussions about the different properties of different sealing grease types, but don't remember any real reason stated for not doing it in your case.

Paul

 

[Teal68]

This is so frustrating! I wish I was better at electrical! Everything checks out fine at the clip, but the minute I hook the clip into the the circuit board the voltage drops to only .3 volts into and out of the gauges. I'm at a loss!

While I had it apart I bench tested the IVR again. It works great. I guess I'l pull each sending unit wire out of the clip and see if that changes anything. If it does I'll replace one at a time and see if I can figure out what the problem is.

BTW, the other stuff in the cluster works fine like the lights and blinker lights. It's just the gauges giving me trouble.

I'll try dielectric grease on the clock points. If it does not work I can clean it off.

 

[DirtDonk]

Yep, but it's not likely to fix this issue anyway. Just there for long-term protection.
Maybe your cluster is not grounded to the chassis during testing? Or at all?
Find out how it's supposed to be bonded (grounded) to the rest of the system and make sure that is functioning. Many older vehicles from all the major manufacturers were known for losing their dash ground or their cluster ground, or their heater control ground where applicable, making those things work intermittently if at all.

Paul

 

[Teal68]

Well Paul, I have dug a bit deeper and may have found a problem. But first, to answer your question, the IVR grounds thru one of the wires in the clip and it ohm's out so that is good. Here's the problem I have discovered....I get 12 volts, actually maybe a bit less (read clue!), to the supply wire for the IVR when the key is on, but I also figured out that the same wire will ohm out to ground. That don't seem right!

 

[DirtDonk]

Not necessarily a problem. This is why using ohms for every aspect of electrical testing does not tell the whole tale.
You can get zero resistance to ground on many positive circuits. But it still has enough resistance to not short to ground when energized. First time I came across that I was just checking wires (in order to learn what was what) that were working perfectly fine. No short circuits, but a direct to ground reading with an ohm-meter.

I'm not sure about the theory, so one of the others like Viper or Steve or someone who's familiar with that territory will have to clarify it for both of us.
I never learned what it was, I just learned that it's not always as it seems.

If you get to within about 1/4 of a volt to battery voltage at that wire, it's probably not causing your main issue. Optimally all wires should show full battery voltage, but in the real world of older wires you often see several points of loss. Especially on the longer wire runs.
But at anything over a 1/2 volt loss, I usually look to fixing that circuit. Either correcting a loose or corroded connection or deteriorated section, or just replacing the whole thing.
At less than 1/3 volt loss I don't usually concern myself too much on the older rigs. Adding computer controls, such as those for an EFI conversion however, I would tolerate much less of a voltage drop.

Anyway, before you dig too deep or pull any more hair out, wait for someone to fill us in on why you can get a low resistance to ground reading through a positive circuit.

Paul

 

[Teal68]

Oh man, I wish I had seen this sooner. I may have messed up! I cut the wire to the IVR to isolate it, and it appears to be some kind of resistance wire! It has just a single, thin, stiff wire in the insulation. I'm hoping it's okay to crimp it back together.

What you say about resistance makes sense. Things like a light bulb in a circuit could probably allow it to ohm out.

 

[DirtDonk]

Strange. The wire feeding the IVR should not be a resistor wire. The only one I'm aware of is between the ignition switch and the stock ignition coil. All other wires should be normal to pass the full 12v where applicable.

What color is the wire?

Paul

 

[Teal68]

I can't remember what color it is, but I'll look next time I have it apart. From looking at a schematic it appears the wire comes from the ignition, and it has a zigzag in it so maybe that means it is a resistance wire?

Anyhow, I got aggravated and put a mechanical oil and temp gauge on it so I could drive it some while I wait on parts.

As usual...Thanks for your help, and I'll update as I get into it again.

 

[DirtDonk]

Yes, a wire from the ignition switch to the engine compartment with a zig-zag and most likely it's own heat resistant outer jacket is indeed the ignition resistor wire. No other wire I can think of that would be on a Bronco like that.
Would be a combination of Red w/green stripe and typically an off-Brown or off-Pink color over much of it's covered length.

In some years the wire leaving the switch was the appropriate Red w/green, while in others the resistor wire went right into the switch in it's odd color.
Once it reaches the firewall it changes back to Red w/green and runs to the coil's positive side.
Should have nothing to do with the instrument cluster or it's IVR, unless spliced into somewhere that it likely should not be.

Paul