Not getting 12 volts. Please Help!

[Clunker]

After several hours of poking around my F250 trying to figure out why my fuel gauge isn't reading correctly (or any of my other gauges for that matter, I finally pulled the instrument panel and found that all of my instruments are only getting 9.7V. The battery has a full 12V and charges at 14V like it's supposed to, but what power source did the previous owner use to power everything? It totally makes sense now, why the gauges are not reading correctly. Can someone please tell me the source of the 10V supply, so I know where to re-rout the wiring? Thanks

[bluef250]

Do a search for Instrument Panel Voltage Reg http://www.fordification.com/forum/view ... p?p=484136 . The truck voltage should be reduced to about 5 volts by IPVR. The gauges run at 5 volts. The IPVR is generally attached to the rear of the instrument panel. . If you have 10 volts something is definitely wrong and you could end up burning up the gauges.

[Clunker]

Sorry. I should have given all of the details. These gauges are aftermarket, and they are supposed to operate at 12V. After looking at the manufacturer's website, I found that the fuel gauge is designed for use with the original stock sending unit, and my tank setup is all original. The IPVR is nowhere to be found behind the instrument panel, so I assume that the previous owner who installed the gauges removed it during the installation. I just completed more testing and found that the instrument panel has two power sources (one for the back-lighting and one for switched 12V). Both are reading 12V when they are disconnected from the instrument panel. But as soon as I hook up the panel, both the lights and gauges are only getting 9.7V, so I think the problem is in one or more of the gauges (or more probably in the amateur wiring job).

After a little online research, I now understand that the IPVR was used to convert the 12V power to 6V because Ford's gauges operated at the lower voltage even though the rest of the truck was using the 12V power. The sending unit is still getting 5V, so maybe there is still an IPVR somewhere.

[colnago]

Clunker,

What aftermarket gauges do you have? Calfdemon just posted a project where he put in AutoMeter gauges into his cluster. I didn'r read all of it, since I have stock F600 gauges, but you might find some pearls of wisdom in seeing what he did. I might use the AutoMeter tach, if I can find a clock that looks good with everything.

Joseph

[Clunker]

Thanks colnago. AutoMeter is the brand of gauges that I have, as well. I'll definitely check out Calfdemon's project.

[Calfdemon]

I sent this to you in a PM as well, but you need to run direct power to your aftermarket gauges and NOT run it through the existing dash power wiring. I did it through the use of relays (as I did with several things in my truck). Here is a link to my thread from a couple of years ago: http://www.fordification.com/forum/view ... =6&t=59539

[Clunker]

Not sure that I understand why I should run a dedicated 12V line to the gauges when I already have 12V available from the factory wiring, but I have a few 20A relays, so I'll give it a shot. I've tried everything else to no avail, and it's a pretty simple installation. Thanks for the advice. I'll keep everyone posted.

[Calfdemon]

The factory wiring can lose some voltage though depending on how many things it is running through. I was talking about the factory power that went to the dash though. I said to bypass that because it runs through the voltage regulator on the back of the dash, but you said that is already gone. The other problem that our trucks had is that everything that turns on once the truck is started is run through one ignition wire and then spiced off from there. An example of this is the 3 prong "accessory plug" that they have after the ignition. They really did not expect anything extra to be added to our trucks back then other than the radio and windshield wipers. The voltage draw on the stock wiring is extremely easy to tax with the way it is designed. This is why I ran separate relays for pretty much everything extra I have added to the truck.

Just curious, but what all do you have installed on your truck that draws power? This might be why you are getting voltage changes, because the stock wiring just cannot handle the draw. One relay should work for all of your gauges and then at least you can be sure you are getting a directy 12v to them without anything else drawing from the same circut.

[Clunker]

Bingo! I ran an independent line directly from the battery and ran it through its own fuse and a relay for the gauges. I also ran the instrument lights through their own relay. Gauges and lights are now getting the full 12V with everything hooked up. Thanks so much for the advice. Let it be known to all who install aftermarket gauges; RUN A SEPARATE 12V LEAD DIRECTLY TO YOUR GAUGES VIA A RELAY. I still don't understand why it worked, but at this point, I don't really care as long as it worked. Do you think that a 15A fuse and 14AWG wire is sufficient to power both the gauges and instrument lights?

Unfortunately, I discovered another problem while doing all of the wiring. For some reason, the ignition switch turns everything on at the "Acc" position (gauges, blinkers, etc.). It's my understanding that the "Acc" position should only turn on things like the stereo, while the "On" position should turn on everything. The previous owner who installed the gauges did a respectable job, considering he was an amateur. But whoever installed the stereo obviously didn't have the same skills or knowledge. I'm betting that I'll find some wires crossed that shouldn't be crossed behind the stereo, but that will have to wait until next weekend. Also, even though the voltage gauge is reading correctly now, the fuel gauge is still not accurate. The impedance of the sending unit is correct, but I'm thinking that maybe the float is no longer floating. When I pulled the sending unit I didn't hear any liquid in the float, so any other suggestions are welcome.

To answer your question about what aftermarket electrical stuff has been installed, only the stereo, the Pertronix ignition, fog lights (with their own wiring), the tow package, the instrument panel, and the instrument lights. Everything else is stock as far as I can tell.

[colnago]

Does your fuel gauge work at all? My truck has an aftermarket sending unit, and the arm isn't as long as the stock arm. Because of that, it doesn't float in the same places that the stock unit floated. So, my gauge is good for ballpark, but it is never really, truly spot-on. If you pull out the sending unit and bend the arm, you might get closer. I just let mine do whatever it wants to do, and I keep an eye on it to make sure it doesn't hit the "E" on the gauge (it's pretty accurate at the bottom end).

Joseph

[Clunker]

The fuel gauge works, but it always reads less than half of what is actually in the tank. I think the sending unit is stock. Its range of motion covers the full height of the tank and its impedance is correct. I also have two tanks, and it's possible that one of the previous owners wired the selector switch incorrectly. The second tank hasn't been used in years, so I don't want to tinker with it until I've had a chance to pull it and clean it.

I just remembered that I already tested the current impedance of the sending unit, and it was 15 ohms with the tank somewhere between 2/3 and 3/4 full. That should be about right for that level of fuel, so the float is probably fine. Probably another wiring issue.

[Clunker]

***Update***

Fixed it. The culprit was the harness that attaches to the fuel tank switch. One or more of the female spade connectors embedded in the harness is so old, oxidized, and worn out that it was giving me a resistance of more than 20 ohms. The toggle switch tested out fine, so I cut the wiring harness and attached new spade connectors to the wires. Problem solved.

[Calfdemon]

Just remember the lesson you learned with these trucks, which is the same lesson I learned: Relays are your friend. The stock wiring in our trucks is barely enough to handle the few items that came with them stock. Anything that you are going to run aftermarket, run a relay with a dedicated power source and just use the stock wiring to open/close the relay.

[Clunker]

I couldn't agree more. Now that all of the gauges are fully functional and accurate, I plan to go through the rest of the electrical to make sure that everything is getting the power that it needs. To start, I'm going to rewire the stereo because it looks like an accident waiting to happen. Then I want to make sure that the electronic ignition is living up to its full potential.