Question About Automotive Ground

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Joined May 22, 2019
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Not true at all. For most cars (specially pre 2010) unless the controls are on the steering wheel itself then they do not run through the clock spring.
That's possible. I know with my 99 everything on the turn signal went through the clock spring along with what was on the steering wheel. There is also a connector plug from the spring that goes in to the connector at the ignition switch.
 

Thread Starter

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Joined May 22, 2019
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Yes a circuit can find a ground through another circuit if the circumstances are right. "Bad ground" is bad terminology just like everything is a "short circuit". Electrical problems in a vehicle can be classified by open, short to ground, short to power, short to another circuit, excessive resistance and parasitic draws. So which one do you have. If you have a circuit that doesn't work and you suspect the ground, try to measure voltage drop across the ground. If you put your meter on DCV and put your negative lead on the ground "Stud" or "Post" of the battery(not the clamp) and the ground side of the load device, energize the circuit. If you have full voltage, you have an open. If you have <0.3VDC, ground should be good if circuit is complete. If you have >0.3VDC, you have excessive resistance. There are some exceptions to the rule but that is a quick and easy way to figure out if you have a "bad" ground. Classify it as something. If ground is good, check voltage going to the hot side of your cranking circuit. This is the heavy load side. Check voltage to the "S" terminal for your solenoid. This is your control circuit. Those 3 tests will get you going in the right direction. The dome lamp can be diagnosed the same way. Good luck.
It's not my vehicle. I would have followed the procedures in the manuals. Those with an opposing view wrote it off as a bad ground and looked no further beyond playing with wires until it started working right. My opinion, nothing got fixed. My opinion from what was described was a short to another circuit.
 

narkeleptk

Joined Mar 11, 2019
480
but it doesn't say anything about the necessary relationships needed to start the vehicle.
The schematics from ford are fairly complete. All links can be found the info is just on other pages. I didn't bother adding others. Bit my fault since I know the starting systems pretty well for fords I just assume its not needed information to make my point that its not going to be anthing with the dome lights ground.

Again, your ignition schematic shows nothing about the clock spring but all the electrical connections in the steering column go through it
None of these run through the clock spring unless they are built on the steering wheel. Are f150's built on steering wheel? I don't remember.


One page won't do it. And even then, you may not have it all. The PATS system for example (anti theft) is almost completely left out of all the manuals. Much of the PATS system was dealer restricted as well. They didn't have access to the information. It was a remote IDS repair or just replaced and reprogrammed for the vehicle.
I am very familiar with PATS. They are not left off schematics at all and are no secret. Anyone can pay motorcraft and download the schematics. I just don't have the 01 F150 schematics on hand and the F250 did not have PATS that year that is why its left off and I mentioned it was. 01 F150 is also OPTIONAL so it would be best to verify if the truck has it first.
 
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narkeleptk

Joined Mar 11, 2019
480
Now fortunately a lot of this has all changed. At this time most of this type of information was considered proprietary. That's changed thanks to the Europeans. Through what the EU called Blocking Legislation if the US wanted to sell vehicles in Europe that had to open all this up. Back in 2,000 it was considered next to impossible to swap engines between vehicles with different PCM's\ECU's. Everybody is doing it now though.
Are you in the EU?
Its actually a lot harder in EU I will give you that. In the states we have better laws to protect aftermarkets right to repair and anybody can register and pay to access the same repair schematics and manuals as the dealers use. Some security issue's require registering with NASTF only to PERFORM but this is easily done. Changing ecu's or programming immobilizers is common practice here. In EU these things are more restricted and requires a little more effort but still well known inside the trade.
 

WBahn

Joined Mar 31, 2012
26,398
Thanks for the replies. I don't understand replying to multiple quotes here so please don't think I'm ignoring anyone here. I'm not.

This is not a fuse or relay issue. I'm also not confusing voltage with current.

Kirchhoff's Law states the sum of the voltage applied to a circuit is equal to the sum of the voltage drops across the circuit.

If ground or chassis ground in a vehicle is a zero voltage reference than a circuit is not going to send voltage through the ground to find some oddball connection back to continuity for the ignition circuit. For lack of a better way to say it, per Kirchhoff's Law the zero voltage reference is the defining end point of the voltage applied to a circuit. Voltage is not going to be added to a circuit to find some way through ground to complete the circuit. I hope I'm making sense. This is also all DC. There is no alternating current.
You can call any point in the circuit you want the zero voltage reference point -- the circuit neither knows nor cares. So any description or understanding of the behavior of the circuit that relies on claims about a particular point being the zero voltage reference point and something not being able to happen as a result are fundamentally invalid.

IF we had a schematic of the vehicle electrical system, we MIGHT be able to make some reasonable guesses about what might cause this behavior. It conceivably could be a connection somewhere such that turning the dome light on changes the voltages at certain points in the network and, as a result, some other component in the network now behaves differently. But, most likely, it would take a bit of time making voltage and current measurements at various places, guided by the schematics, to track it down.

It might be worth spending some time trying to determine if there are other things instead of the dome light that can cause the observed behavior. If there are, noting what those components have in common might help.
 

WBahn

Joined Mar 31, 2012
26,398
Wow, not at all what I've dealt with for years. Corroded contacts or connections for one. They create a lot of resistance, suck up power and get hot. I've seen more that one car catch on fire because of a short.
A "lot of resistance" is relative. Connections are intended to have extremely low resistance. The power dissipated in the connections is I²R where I is the current and R is the resistance. If R is very close to zero, then you can have lots of current but very low power dissipation. As the resistance starts to increase, the current through the circuit will generally decrease but, even with the lower current, the heat dissipated in the connection increases. It can increase significantly before the increasing resistance lowers the current sufficiently to start bringing the power dissipated in the connection back down. But the point at which this happens would still not be considered "a lot of resistance" by most measures.
 

MisterBill2

Joined Jan 23, 2018
8,030
The whole thing with the dome light might also be an anti-theft feature added by somebody. That has been done by at least one that I know. Another arrangement that worked well was having the lighter socket wired across the breaker points. Park the car and push in the lighter and not even a hot-wire attack could start the engine. The engine would crank over but never catch. A really cheap anti-theft trick for a high school kid to use. But it is not applicable for cars today.

And as for "ground", it is a theoretical concept of a zero-impedance plane tied perfectly to some zero voltage point. That is why "common" is a better term that is still not really completely accurate.
 

Thread Starter

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Joined May 22, 2019
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I am very familiar with PATS. They are not left off schematics at all and are no secret. Anyone can pay motorcraft and download the schematics. I just don't have the 01 F150 schematics on hand and the F250 did not have PATS that year that is why its left off and I mentioned it was. 01 F150 is also OPTIONAL so it would be best to verify if the truck has it first.
That's true now but it wasn't in at the time. At the time Ford didn't even put the 00 chapter in the workshop manuals for PATS.
 

Thread Starter

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You can call any point in the circuit you want the zero voltage reference point -- the circuit neither knows nor cares. So any description or understanding of the behavior of the circuit that relies on claims about a particular point being the zero voltage reference point and something not being able to happen as a result are fundamentally invalid.

IF we had a schematic of the vehicle electrical system, we MIGHT be able to make some reasonable guesses about what might cause this behavior. It conceivably could be a connection somewhere such that turning the dome light on changes the voltages at certain points in the network and, as a result, some other component in the network now behaves differently. But, most likely, it would take a bit of time making voltage and current measurements at various places, guided by the schematics, to track it down.

It might be worth spending some time trying to determine if there are other things instead of the dome light that can cause the observed behavior. If there are, noting what those components have in common might help.
I'm with you on actually taking voltage and current measurements instead of jumping to bad ground. Not my vehicle though and I have no control over what the guy does.

I can't argue the point of the meaning of zero voltage reference and possibilities but in automotive work it's a generally accepted principle. If more than .5 volts is measured at ground something is wrong or with everything off current should be 30 ma or less. If this isn't what's being read perform a parasitic draw on the battery by circuit at the fuse panels. This is something the person with the problem did not do. This should identify which circuits are involved with this dome light problem.

I'm sure with more knowledge of electric and electronic issues this may seem overly simplified but it works. My automotive history is with Chassis and suspension design so I freely admit my ignorance with electricity. What little I do know though has worked for me so far.

From my own experience though oddball electrical issues like the one here are too often just written off as bad ground and by going through the processes I do know bad ground is usually not the issue. More often than not I find shorts between circuits that show up with testing the voltage at the fuses. Since ground is common for every circuit in a vehicle every circuit ground can be measured anywhere at the chassis, body or engine as long as it's properly grounded. Again, something that was never checked in this dome light issue.
 

Tonyr1084

Joined Sep 24, 2015
5,722
I wasn't referring to corrosion as a short and not to the point that it's an open. Apples and oranges. I was just referring to heat here. And as I said, I've seen shorts cause fires. Heat.
When I was around 10 to 12 years of age I found some very old relays. When energized they pulled in immediately. But when de-energized they took (guessing) around 500 mS to disengage. When I wired the relay through the NC contacts it would clock pulse, though it wasn't designed to do that (that I know of). I was powering that relay using an old car battery my dad had laying around. The wire I used was a small gauge wire, probably on the order of 20 gauge. Without realizing it - one time I ended up shorting the battery (SHORT) from positive to negative through that small wire. The INSTANT result was a wire that was way too hot to hold - and just about all the wire inside the insulation melted. I know what a short is and what it does.

Yes a circuit can find a ground through another circuit if the circumstances are right. "Bad ground" is bad terminology just like everything is a "short circuit". Electrical problems in a vehicle can be classified by open, short to ground, short to power, short to another circuit, excessive resistance and parasitic draws. So which one do you have. If you have a circuit that doesn't work and you suspect the ground, try to measure voltage drop across the ground. If you put your meter on DCV and put your negative lead on the ground "Stud" or "Post" of the battery(not the clamp) and the ground side of the load device, energize the circuit. If you have full voltage, you have an open. If you have <0.3VDC, ground should be good if circuit is complete. If you have >0.3VDC, you have excessive resistance. There are some exceptions to the rule but that is a quick and easy way to figure out if you have a "bad" ground. Classify it as something. If ground is good, check voltage going to the hot side of your cranking circuit. This is the heavy load side. Check voltage to the "S" terminal for your solenoid. This is your control circuit. Those 3 tests will get you going in the right direction. The dome lamp can be diagnosed the same way. Good luck.
Thanks B! My points exactly. A "Bad Ground" is either "very high resistance" or an "open circuit".

A friend owned a Plymouth Duster. That car - you could turn the four way flashers on and the radio would play, but only when the flashers were either ON or OFF - I don't remember exactly which. But yes, one circuit can find a current pathway through another circuit. In the case of the Duster I don't know if the flashers were back powering the radio or were providing a pathway to ground. Given back in the 70's what I knew then of auto electrics I'd say the flashers were back feeding power to the radio.
 

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The schematics from ford are fairly complete. All links can be found the info is just on other pages. I didn't bother adding others. Bit my fault since I know the starting systems pretty well for fords I just assume its not needed information to make my point that its not going to be anthing with the dome lights ground.


None of these run through the clock spring unless they are built on the steering wheel. Are f150's built on steering wheel? I don't remember.



I am very familiar with PATS. They are not left off schematics at all and are no secret. Anyone can pay motorcraft and download the schematics. I just don't have the 01 F150 schematics on hand and the F250 did not have PATS that year that is why its left off and I mentioned it was. 01 F150 is also OPTIONAL so it would be best to verify if the truck has it first.
Per FOMOCO, The F250 had PATS as of 1999.

As of 1999 it was on the steering wheel with the actual module integrated on to the instrument cluster, Before that the module was under the dash.
 

bwilliams60

Joined Nov 18, 2012
1,382
Zero Voltage Reference was actually brought into the automotive industry when modules started to become the norm. It was a term they used for the ground inside themodule that was used for sensors. Confused the hell out of everyone. It was actually just a clean ground run directly from the battery.
It has now adapted itself to the battery negatice post which in automotive speak, now represents the most negative point on the vehicle, hence Zero voltage. Once you leave the battery post, the circuit starts to become more positive and an allowance of 0.3VDC is acceptable on a ground circuit. The chassis, engine and frame are not acceptable measuring points when diagnosing unless they have been confirmed as having no voltage drop to the battery negative post.
This is why Imsaid, if you suspect you have a bad ground, measure the voltage on the negative side of the circuit with reference to the battery negative post. It will be good, excessive resistance or open. Not "bad".
 

narkeleptk

Joined Mar 11, 2019
480
Per FOMOCO, The F250 had PATS as of 1999.
F250 and bigger did not have PATS til about 2008 with the exception of the 99-00 f250 under 8500 GVW.
The F150's started MY1999 in the cluster. It was an option on many early f150's however so not all of them have it. Pretty much since 04 its been standard on f150's tho.

The earliest FORD in the US to get the first PATS system would be the mustang and taurus late build 95's so MY1996. These PATS 1 models did indeed use a stand alone module.

Interesting fact about when we where discussing how immobilizer where super secretive and impossible to work on:
Did you know, there are no tools required and nothing to replace when programming a new key after all keys are lost on the PATS 1 system? Just need turn the switch and have a proper key (any with tex 4C transponder chip) and a little time.

This info is for the States only. EU is different and uses different systems then we do.
 
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Thread Starter

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An update:

I got another response today from an acquaintance at Ford FEL, Engineering Lab, and he said this sounds like a programming issue with keyless entry\alarm. He added that with these older vehicles the fobs get lost over the years and because of their price people often just do without them. As the vehicles get sold and sold again the keyless entry is an option that owners aren't aware they have until they have a problem. Because the dome light is part of the door latch circuit this is how it's tied to this problem. I messaged the person with the problem and he isn't aware of any OEM keyless entry but his father did add an aftermarket keyless entry. Although I don't know with never actually seeing the truck I imagine this is what explains the problem the truck owner was experiencing. The aftermarket keyless entry is also something he never mentioned.
 

narkeleptk

Joined Mar 11, 2019
480
The aftermarket keyless entry is also something he never mentioned.
OEM shouldn't cause any issues on these since it only makes the horn beep and does not disable anything but those aftermarket ones are pretty nasty indeed and cause all kinds of problems. Wouldn't surprise me at all if its part of the problem and is having some issue's connected with the door ajar sense.
Thanks for the update. I'm always overly interested in these types of things.
 
Is there like "retained power" on this thing? e.g. GM where you turn off the car and the radio works untill the door is opened.

What if the keyless entry was connected to "retained power" or something similar.
 

narkeleptk

Joined Mar 11, 2019
480
Overlooked answering this when first asked. Yes, I spent most of my career working in England and Germany. Retired now and back in the US.
EU models are quite different in many ways. Mostly relating to security systems and aftermarket inclusion from what I can tell. Trying to relate the two markets usually causes a lot of confusion on the international auto forums I frequent.
 

Thread Starter

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Joined May 22, 2019
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Is there like "retained power" on this thing? e.g. GM where you turn off the car and the radio works untill the door is opened.

What if the keyless entry was connected to "retained power" or something similar.
This shouldn't be an issue. Had the person with the problem followed procedures per the manuals and started with testing for parasitic draws on the battery and chased it to the circuit through the fuses the procedures remove this possibility.
 

Thread Starter

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Joined May 22, 2019
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EU models are quite different in many ways. Mostly relating to security systems and aftermarket inclusion from what I can tell. Trying to relate the two markets usually causes a lot of confusion on the international auto forums I frequent.
I worked primarily in rallying where much of what you're referring to didn't apply but I'm well aware of what you're getting at.
 
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