Improving Volt Gauge Accuracy***Split From Wire Selection...***

[DMC5180]

Hmm, would this explain why my Volt Gauge consistently shows about .5 Volt less than what my DVM says when measured in the engine bay? (Line Loss or just a crappy gauge). I guess the only way to be sure would be to connect a stand alone factory gauge parallel to the DVM and see if the readings more closely line up.

[DMCMW Dave]

Hmm, would this explain why my Volt Gauge consistently shows about .5 Volt less than what my DVM says when measured in the engine bay? (Line Loss or just a crappy gauge). .

You can't really expect an antique analog gauge that is connected with corroded wiring and several teminations to come close to matching the reading accuracy of a modern DVM other than by lucky accident. Unless it's a Harbor Freight DVM.:what_the:

[DeLorean03]

Dave D: !!!!! Some of us are strongly attached to our antique gauges ;).

To accurately measure the voltage on the DeLorean's binnacle voltage gauge, we would just measure the voltage directly on the battery - correct?

[DMCMW Dave]

Dave D: !!!!! Some of us are strongly attached to our antique gauges ;).
To accurately measure the voltage on the DeLorean's binnacle voltage gauge, we would just measure the voltage directly on the battery - correct?

The battery is the reference voltage point for the whole car. It's all downhill from there.

I've seen cars where you could change the voltage reading on the dash simply by wigging the fuse that feeds it. This is because it is at the far end of a shared circuit with current flowing through it. If the meter was very high impedance (like a DVM) AND on a dedicated circuit to the battery, resistance in that circuit (within reason) would not impact the voltage reading.

EDIT so to answer Dennis' comment, a DVM right across the factory meter would tell you how far off the meter is, and would show the same errors due to the loading of the shared circuit.

[DMC5180]

The battery is the reference voltage point for the whole car. It's all downhill from there.

I've seen cars where you could change the voltage reading on the dash simply by wigging the fuse that feeds it. This is because it is at the far end of a shared circuit with current flowing through it. If the meter was very high impedance (like a DVM) AND on a dedicated circuit to the battery, resistance in that circuit (within reason) would not impact the voltage reading.

EDIT so to answer Dennis' comment, a DVM right across the factory meter would tell you how far off the meter is, and would show the same errors due to the loading of the shared circuit.


This confirms my thought then. Not necessarily that it shows the meter being OFF. The gauge is relatively accurate if measured Apples to Apples with a secondary device (DVM) at the same location. Line loss is the reason for the lower than actual Charging system voltage.

Isolating the OEM gauge to a single Dedicated battery circuit would remove as much line loss as possible if the wires are oversized slightly to say 14 AWG and connections cleaned..

[DMCMW Dave]

This confirms my thought then. Not necessarily that it shows the meter being OFF. The gauge is relatively accurate if measured Apples to Apples with a secondary device (DVM) at the same location. Line loss is the reason for the lower than actual Charging system voltage.

Isolating the OEM gauge to a single Dedicated battery circuit would remove as much line loss as possible if the wires are oversized slightly to say 14 AWG and connections cleaned..

If you ran a dedicated wire AND GROUND to the gauge it would make a world of difference. The problem with the gauge as-installed (in addition to being old) is the shared load on the circuit. Obviously you could come close to the same benefit if all the connections in that circuit were just good. The current draw of the gauge itself is tiny, if it was fed alone the wire could be very small so I see no need to oversize the wiring if it is truly a dedicated-to-the-gauge circuit. That all being said, I'm not sure (without looking) that you can really isolate the gauge without cutting up the circuit board on the cluster.

[Bitsyncmaster]

If you remove the ground wire on the inertia switch and move it to the frame for ground, that will remove 7 amps flowing in the same ground wire used for the dash gauge. That will bump up your gauge volt meter 0.3 volts. My gauge reads just below 15 volts as does reading the voltage on the jump terminal with my DVM.

Note, John's power pump runs a little above 10 amps. Wonder what the new DMC pump draws.

If I were going to the effort to install new wires, I would use 12 AWG for the pump. You can calculate the difference in voltage drop using Dave's estimate of 25 feet total.

Frame ground is pretty good. Low resistance to the battery neg so voltage drop is pretty small.

[DMCMW Dave]

If you remove the ground wire on the inertia switch and move it to the frame for ground, that will remove 7 amps flowing in the same ground wire used for the dash gauge. That will bump up your gauge volt meter 0.3 volts. My gauge reads just below 15 volts as does reading the voltage on the jump terminal with my DVM.
.

That's the point I was going for. Nobody ever thinks about the shared ground path but it's a huge deal on this car. Dennis - this is probably the fix you are looking for to get the gauge reading properly. If you are concerned about eliminating the intertia switch, you could always upgrade the ground to the inertia switch and leave it in the fuel pump circuit.

[Bill Robertson's Sock Puppet #1]

If you remove the ground wire on the inertia switch and move it to the frame for ground, that will remove 7 amps flowing in the same ground wire used for the dash gauge. That will bump up your gauge volt meter 0.3 volts

Don't forget the windshield wiper motor, also ganged onto the same ground junction (don't know how many amps it draws). Turn signal bulbs are ganged there as well via the flasher module. And the dash illumination bulbs. Plus a few other driver side odds & ends.

[DMC5180]

That's the point I was going for. Nobody ever thinks about the shared ground path but it's a huge deal on this car. Dennis - this is probably the fix you are looking for to get the gauge reading properly. If you are concerned about eliminating the intertia switch, you could always upgrade the ground to the inertia switch and leave it in the fuel pump circuit.

Yeah, pretty much. This seems like the path of least resistance (pun intended) in more ways than one. IE: a simple job to perform.


Don't forget the windshield wiper motor, also ganged onto the same ground junction (don't know how many amps it draws). Turn signal bulbs are ganged there as well via the flasher module. And the dash illumination bulbs. Plus a few other driver side odds & ends.

Good to know but I'm not to concerned with intermittent load items. The Fuel Pump on the other hand is always running.

[Bitsyncmaster]

Here is where I frame grounded my inertia switch.

[DMCMW Dave]

We see cars in here from time to time with the pump grounded via a sheet metal screw in a new hole drilled just above the steering rack. Yuck on several fronts.

I usually assume that the inertia switch got tripped, and some prior tech could not find it and "fixed the car" the quickest way possible.

[Elvis]

I had low readings at load, too.
Using different wires and measuring locations is a solution for sure - to get a better reading of the gauge.

BUT originally it die read pretty well, so if it reads too low under load - get rid of the losses !

Am I the only one who has problems with the GND connection below the water bottle in the engine bay ?

Also the +12V screw and GND screw which feed the interior of the car should be clean.

[Bill Robertson's Sock Puppet #1]

Am I the only one who has problems with the GND connection below the water bottle in the engine bay ?

That particular connection grounds almost the entire vehicle. Only the engine itself (not fuel pump, frequency valve, or ignition ECU) and the radiator fans (plus a few other items grounded to the front radiator bracket, such as the trunk light) have a different path to ground. If that connection degrades or is lost, basically the entire car degrades or is lost.

Note that the battery regrounding wire that some vendors sell does absolutely nothing to compensate for loss of the ground under the coolant expansion tank, or the rear bulkhead bolt at the other end. That wire regrounds the frame (or the engine, depending upon where it is attached) only.

[David T]

The voltmeter (or any of the instruments in the dash for that matter) are not high precision quality indicators. And that was when they were new! All those gauges are meant for is to give you a general indication of what is going on with the vehicle. Even the speedometer is only calibrated within 5% and then only at 60 MPH. What they are useful for is if something is going wrong they will tell you because they will not be indicating in the range of where they normally do. In the case of the voltmeter you may also have the charging light on and everything will seem dimmer. That is called "Cross-Checking". As for the subject of grounding, EVERY Delorean should have it's grounds cleaned and checked regularly. It is SO important because of the way the car is constructed and wired. If you are having problems with your voltmeter it is probably telling you it is time to check and clean the grounding points.
David Teitelbaum

[DMC5180]

The voltmeter (or any of the instruments in the dash for that matter) are not high precision quality indicators. And that was when they were new! All those gauges are meant for is to give you a general indication of what is going on with the vehicle. If you are having problems with your voltmeter it is probably telling you it is time to check and clean the grounding points.
David Teitelbaum

Agreed, the gauges are for general reference only.

My volt gauge readings have been consistently low relative to actual voltage throughout my 17 yrs of ownership. (still running the Motorola though). It would just be nice to see it read the actual voltage or as close as possible. I've seen other cars (D's) show much higher gauge readings 13.7-14.0. But those usually have different alternators with higher regulated settings of 14.2 -14.6 regulated voltage. With mine voltage seems to be regulated to about 13.87 or so. but the gauge shows 13.2.-13.3 never higher. Running loads (headlights/fans) 12.8-13.0V. Hopefully the moving of the FP ground will address this. Other grounds will be checked and cleaned too. I will try and verify net results for each ground point cleaned as I move through the car. It'll be interesting to see where the biggest gains a made.

[Bill Robertson's Sock Puppet #1]

Don't forget to check connections where the gauge itself contacts the instrument cluster's PC paper with cheap thin unplated folded speed nuts that aren't even threaded. A good investment IMHO is a box of proper brass hex nuts to replace the whole cluster. Thread is 6-32.

[DMC5180]

Don't forget to check connections where the gauge itself contacts the instrument cluster's PC paper with cheap thin unplated folded speed nuts that aren't even threaded. A good investment IMHO is a box of proper brass hex nuts to replace the whole cluster. Thread is 6-32.

The last time I had the cluster out the all the PC tabs appeared to be nice and clean copper. The Harness connector contacts looked pretty good too. I will look into the Brass nuts. I assume brass star washers would make sense too. I understand the PC is very thin. I will be cautious when snugging down the nuts.

[Bill Robertson's Sock Puppet #1]

The problem isn't the PC paper -- it's the nuts. Many years ago I had a situation where my dash volt gauge read about 8 volts, but a digital meter plugged into the defroster harness connector confirmed the alternator was in fact charging. Problem turned out to be a loose speed nut on the gauge itself.

[David T]

One good upgrade is to replace the oil pressure sender for the gauge. The OEM stock sender keeps the oil pressure gauge pegged all the time. The replacement gives a more accurate indication, ie, when idling it does read lower. Even so it is not what I would call accurate, just a good indicator. As for the electrical gauges, there are so many connections, including the PC foil, that a problem on any or all is cumulative and eventually results in lower readings. Keep in mind that we are talking about a car that is 30 years old and maybe spent a good part of it's life outdoors. Things corrode.
David Teitelbaum

[Bill Robertson's Sock Puppet #1]

Dash volt gauge:
+: Fuse #5, Green junction under console (soldered), instrument cluster harness connector, gauge.
-: Gauge, instrument cluster harness connector, ground junction behind HVAC duct (soldered), rear bulkhead bolt onwards (shared with just about every other grounded device on the car).

[Bill Robertson's Sock Puppet #1]

Correction: Instrument cluster does not pass through the Green junction under the console. On the positive side it's a straight shot from Fuse #5 to the harness connector.

[kings1527]

One good upgrade is to replace the oil pressure sender for the gauge. The OEM stock sender keeps the oil pressure gauge pegged all the time. The replacement gives a more accurate indication, ie, when idling it does read lower.

I just replaced my oil sending unit about a couple months ago and documented the whole thing:

http://delorean6575revisited.blogspot.com/2012/10/replacing-oil-sending-unit-and.html

It was very simple and cheap to do. And like David said, the oil pressure gauge is more accurate now and doesn't peg when it's idling! Or at all, for that matter.

Alex
6575

[kings1527]

So I re-grounded my inertia switch to a body bolt on the driver's side center console, anticipating a jump in the volt meter. Not so much. I'm about 13.5V right now, which is much better than my previous 12.6-12.8V or so. But I think my big improvement was due to Hervey's double ground wire. After installing that, my meter jumped to 13.5V or so. But after I re-grounded the inertia switch, I don't remember it changing again at all. :hmm: And I know it's grounded well, otherwise my car wouldn't start (been there).

Not a big deal. I do like the fact that the inertia switch ground is playing on its own golf course now.

[Ryan King]

If you remove the ground wire on the inertia switch and move it to the frame for ground, that will remove 7 amps flowing in the same ground wire used for the dash gauge. That will bump up your gauge volt meter 0.3 volts. My gauge reads just below 15 volts as does reading the voltage on the jump terminal with my DVM.

Hey Dave, Chris Miles here on the forum and I just did this mod to my car. I can effectively say this has increased my voltage significantly and helps keep the needle from moving so much. I am very pleased with grounding the inertia switch via the frame. Now to tackle the running lights by making them all LED. :D

[Rich]

..... My gauge reads just below 15 volts as does reading the voltage on the jump terminal with my DVM....
This is not about what seems to be good accuracy of your dash gauge, it's about the fact that the car seems to be running at about 15.0 Volts.

Generally recommended charging range for auto systems is 12.8-14.7V

Not sure how far below 15V you are running, but it seems your system is running a bit high on voltage. Overcharging tends to be bad for the battery.

[Bitsyncmaster]

This is not about what seems to be good accuracy of your dash gauge, it's about the fact that the car seems to be running at about 15.0 Volts.

Generally recommended charging range for auto systems is 12.8-14.7V

Not sure how far below 15V you are running, but it seems your system is running a bit high on voltage. Overcharging tends to be bad for the battery.

I had a chart posted of typical battery voltage to maintain full charge in the old .com forum. In the winter, 15 volts is more typical and summer, 13.8 volts. My battery is 6 years old. I do think this alternator is a little higher voltage than normal but it has not hurt the battery.

[David T]

15 volts is too much. If it is that high you should get an accurate meter and check with that, not the gauge in the panel. Voltage that high will shorten the life of many of the things in the electrical system including the battery.
David Teitelbaum

[kings1527]

So I think I solved my volt meter under-reading issue. After hooking up several other things on my car, my meter now seems to read perfectly! Here's my recipe for a fully functioning volt meter that worked for me:

1) Hervey's double ground cable, which grounds the negative terminal on the battery to the frame and the transmission.
2) Re-grounding the inertia switch to a location that is occupied only by the inertia switch. This takes it away from where the instrument cluster is also grounded.
3) The grounding location on the right side of the radio bracket. Somewhat of a controversial location after being described by Bill as being insignificant, I could swear that I was reading markedly higher after I re-connected it.
4) 100% LEDs in my car. I don't think this has much of an effect on how high the volt meter will read, but rather how much it dips when you hit the brakes, turn signals, etc. The only time I see my meter drop is when I turn on the headlights and then the alternator (DMCH unit) catches up and puts it right back where it normally is.

That was all it took. Before all of the above, I was reading your standard 12.7V or so. Here's where I'm at now:

17430

[jawn101]

So I think I solved my volt meter under-reading issue. After hooking up several other things on my car, my meter now seems to read perfectly! Here's my recipe for a fully functioning volt meter that worked for me:

1) Hervey's double ground cable, which grounds the negative terminal on the battery to the frame and the transmission.
2) Re-grounding the inertia switch to a location that is occupied only by the inertia switch. This takes it away from where the instrument cluster is also grounded.
3) The grounding location on the right side of the radio bracket. Somewhat of a controversial location after being described by Bill as being insignificant, I could swear that I was reading markedly higher after I re-connected it.
4) 100% LEDs in my car. I don't think this has much of an effect on how high the volt meter will read, but rather how much it dips when you hit the brakes, turn signals, etc. The only time I see my meter drop is when I turn on the headlights and then the alternator (DMCH unit) catches up and puts it right back where it normally is.

That was all it took. Before all of the above, I was reading your standard 12.7V or so. Here's where I'm at now:

17430

That is dead-on where mine lives now too, and I took the same steps except for the inertia switch ground. Congrats! Have you measured your actual battery voltage with all the systems running? Turn on the stereo, headlights, brights and max a/c with all the doors open and measure the voltage at the pick-up post and block. Curious what you see there.

[jawn101]

That is dead-on where mine lives now too, and I took the same steps except for the inertia switch ground. Congrats! Have you measured your actual battery voltage with all the systems running? Turn on the stereo, headlights, brights and max a/c with all the doors open and measure the voltage at the pick-up post and block. Curious what you see there.

Too late to edit my post so... I just measured mine with all the doors/hood/engine cover open, A/C at max (cooling fans on), blower at 4, radio/sub at max volume and headlights/brights on. It was going between 13.9-14.2v at the pickup post/hoist loop but only showed just about 13 at the volt gauge. Not real accurate but a fair indicator of load if you ignore the numbers and know where it 'should' be :)

[kings1527]

That is dead-on where mine lives now too, and I took the same steps except for the inertia switch ground. Congrats! Have you measured your actual battery voltage with all the systems running? Turn on the stereo, headlights, brights and max a/c with all the doors open and measure the voltage at the pick-up post and block. Curious what you see there.

Hey Jon,

Sorry for the late response. That's a great idea and I see what your results were. You've got me thinking, though. I remember that rewiring the inertia switch didn't seem to be a night/day difference and it's interesting that you're getting the same reading without the switch being re-grounded. I think I got a real noticeable difference when I re-grounded the radio bracket bolt, like I mentioned before. I still have my stuff apart so I might do an experiment with that bolt. My courtesy lights aren't hooked up since I'm still putting the interior back together, but probably Wednesday I'll be able to run those tests you were talking about.

And you're right, the gauge probably isn't going to be incredibly accurate no matter what we do but there are definitely ways to get it reading somewhat close!