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gauge silliness #665333 04/09/10 04:18 PM 04/09/10 04:18 PM
Joined: Sep 2007 Posts: 5,037 hi sharpie OP Moparts Linguist
sharpie OP Moparts Linguist Joined: Sep 2007 Posts: 5,037 hi	Okay, interesting problem in the 71 Demon. I have five Auto Meter gauges in my panel - voltage, oil press, fuel level, speedo, water temp. No problems with water temp, speedo, fuel level. But some interesting silliness with the oil pressure and voltage. You see, everything works out beautifully when the car starts and runs. All gauges show correct. But when I pull the light switch to either parking lamps or headlights, my oil pressure and voltage cease to work. Oil pressure buries itself past 100 and my voltage zeros out. No instrument lamps go on in these gauges either. Additionally, the dimmer switch on the light switch can be used to change the values of these gauges. At this point you're probably saying, "haha, this problem's easy! You have it on the instrument lamp circuit!" But that's where I can't figure this out. You see, my instrument lamps and my +12V leads to the gauges are on completely different circuits. Further, and here's the kicker, all the instrument lamps are in parallel with each other, as well as the +12V leads on a separate wire(see photo 1). So you'd assume that if two were having problems, the other three would be, too, because they get their power from the same place. So I decided to trace it - maybe I wired it wrong somewhere? I traced it back, and all of my +12V are going to the Dark Blue with tracer wire (DB* on the chart in photo 2). So not sure what's going on. Maybe a bad ground? Maybe something else. Any ideas as to how to test this?

Re: gauge silliness [Re: sharpie] #665334 04/09/10 04:19 PM 04/09/10 04:19 PM
Joined: Dec 2007 Posts: 7,759 So Cal HealthServices Why would you even post that?
HealthServices Why would you even post that? Joined: Dec 2007 Posts: 7,759 So Cal	Sounds like a ground issue. Allen Here's a novel idea, let's not throw a bunch of parts at the car hoping it will fix the problem and instead spend a little time diagnosing it first. Life was a little easier when I was just a wrench.

Re: gauge silliness [Re: HealthServices] #665335 04/09/10 04:23 PM 04/09/10 04:23 PM
Joined: Dec 2007 Posts: 7,759 So Cal HealthServices Why would you even post that?
HealthServices Why would you even post that? Joined: Dec 2007 Posts: 7,759 So Cal	How are the headlights grounded? Headlight switch? The engine block has a good ground to the firewall? How about the instruments? Allen Here's a novel idea, let's not throw a bunch of parts at the car hoping it will fix the problem and instead spend a little time diagnosing it first. Life was a little easier when I was just a wrench.

Re: gauge silliness [Re: HealthServices] #665336 04/09/10 04:27 PM 04/09/10 04:27 PM
Joined: Sep 2007 Posts: 5,037 hi sharpie OP Moparts Linguist
sharpie OP Moparts Linguist Joined: Sep 2007 Posts: 5,037 hi	Quote: How are the headlights grounded? Dunno Quote: Headlight switch? Dunno Quote: The engine block has a ground to the firewall? The block has a ground to the battery (-) Quote: How about the instruments? The instruments ground through an extra opening in the bulkhead connector and attach to a wiper motor nut/stud. My bulkhead connector may be bad, as could be the grounding point on the wiper motor, I suppose. But why wouldn't they all have issues then?

Re: gauge silliness [Re: sharpie] #665337 04/09/10 04:34 PM 04/09/10 04:34 PM
Joined: Dec 2007 Posts: 7,759 So Cal HealthServices Why would you even post that?
HealthServices Why would you even post that? Joined: Dec 2007 Posts: 7,759 So Cal	Quote: My bulkhead connector may be bad, as could be the grounding point on the wiper motor, I suppose. But why wouldn't they all have issues then? As soon as you pull the headlights on if it has a bad ground, it will look for any ground it can get. this includes the instruments. Remember your oil guage and your voltage guage uses a ground. I'm thinking your headlights is stealing this to complete it's circuit. Assuming it is doing this I would think your headlights are not the brightest either when it is on. Last edited by HealthServices; 04/09/10 05:03 PM.

Re: gauge silliness [Re: HealthServices] #665338 04/09/10 04:35 PM 04/09/10 04:35 PM
Joined: Sep 2007 Posts: 5,037 hi sharpie OP Moparts Linguist
sharpie OP Moparts Linguist Joined: Sep 2007 Posts: 5,037 hi	So you think the headlights have a bad ground, as opposed to the instruments?

Re: gauge silliness [Re: sharpie] #665339 04/09/10 04:37 PM 04/09/10 04:37 PM
Joined: Dec 2007 Posts: 7,759 So Cal HealthServices Why would you even post that?
HealthServices Why would you even post that? Joined: Dec 2007 Posts: 7,759 So Cal	Quote: Quote: The engine block has a ground to the firewall? The block has a ground to the battery (-) Very bad, put another ground from the block to the chasis and another from the battery to the chasis Allen Here's a novel idea, let's not throw a bunch of parts at the car hoping it will fix the problem and instead spend a little time diagnosing it first. Life was a little easier when I was just a wrench.

Re: gauge silliness [Re: HealthServices] #665340 04/09/10 04:38 PM 04/09/10 04:38 PM
Joined: Dec 2007 Posts: 7,759 So Cal HealthServices Why would you even post that?
HealthServices Why would you even post that? Joined: Dec 2007 Posts: 7,759 So Cal	Quote: The instruments ground through an extra opening in the bulkhead connector and attach to a wiper motor nut/stud. My bulkhead connector may be bad, as could be the grounding point on the wiper motor, I suppose. Is this your only ground for the wiring system? How does it get back to the [-] battery? You should also have another ground from the wire harness to the core support, but you still need a wire from the battery [-] to all of this... I mean how does your system get ground if there is nothing going back directly to the battery? You have power going to everything but you don't have ground going to everything. Allen Here's a novel idea, let's not throw a bunch of parts at the car hoping it will fix the problem and instead spend a little time diagnosing it first. Life was a little easier when I was just a wrench.

Re: gauge silliness [Re: HealthServices] #665341 04/09/10 04:45 PM 04/09/10 04:45 PM
Joined: Sep 2007 Posts: 5,037 hi sharpie OP Moparts Linguist
sharpie OP Moparts Linguist Joined: Sep 2007 Posts: 5,037 hi	Quote: I mean how does your system get ground if there is nothing going back directly to the battery? You have power going to everything but you don't have ground going to everything. Good question. I am not sure. I guess it grounds to chassis then chassis to engine then engine to battery?

Re: gauge silliness [Re: sharpie] #665342 04/09/10 04:48 PM 04/09/10 04:48 PM
Joined: Dec 2007 Posts: 7,759 So Cal HealthServices Why would you even post that?
HealthServices Why would you even post that? Joined: Dec 2007 Posts: 7,759 So Cal	Quote: Quote: I mean how does your system get ground if there is nothing going back directly to the battery? You have power going to everything but you don't have ground going to everything. Good question. I am not sure. I guess it grounds to chassis Yes Quote: then chassis to engine How? Quote: then engine to battery? Yes, yes, and yes. You can help it by installing a ground from the chassis to the battery [-] For the gauges to work properly you need a good ground from the chassis to the engine. This would be a good start.

Re: gauge silliness [Re: HealthServices] #665343 04/09/10 04:52 PM 04/09/10 04:52 PM
Joined: Jan 2003 Posts: 32,947 Grand Prairie,Texas stumpy I Win
stumpy I Win Joined: Jan 2003 Posts: 32,947 Grand Prairie,Texas	How are you grounding the gauge lights?

Re: gauge silliness [Re: stumpy] #665344 04/09/10 04:56 PM 04/09/10 04:56 PM
Joined: Dec 2007 Posts: 7,759 So Cal HealthServices Why would you even post that?
HealthServices Why would you even post that? Joined: Dec 2007 Posts: 7,759 So Cal	Quote: How are you grounding the gauge lights? Yes I should not assume he did that either. Allen Here's a novel idea, let's not throw a bunch of parts at the car hoping it will fix the problem and instead spend a little time diagnosing it first. Life was a little easier when I was just a wrench.

Re: gauge silliness [Re: HealthServices] #665345 04/09/10 05:02 PM 04/09/10 05:02 PM
Joined: Sep 2007 Posts: 5,037 hi sharpie OP Moparts Linguist
sharpie OP Moparts Linguist Joined: Sep 2007 Posts: 5,037 hi	there's actually two separate grounds for the gauge panel. One is for all of the lights including the signals and hi-beam lights, the other is for all of the gauges. Each runs through the bulkhead and out to the chassis ground inside the engine bay on the wiper motor.

Re: gauge silliness [Re: sharpie] #665346 04/09/10 05:05 PM 04/09/10 05:05 PM
Joined: Dec 2007 Posts: 7,759 So Cal HealthServices Why would you even post that?
HealthServices Why would you even post that? Joined: Dec 2007 Posts: 7,759 So Cal	Quote: there's actually two separate grounds for the gauge panel. One is for all of the lights including the signals and hi-beam lights, the other is for all of the gauges. Each runs through the bulkhead and out to the chassis ground inside the engine bay on the wiper motor. So there is a ground from the battery to the chassis? Or how is the ground getting back to the battery [-]? Hopefully not thru the motor mounts. Allen Here's a novel idea, let's not throw a bunch of parts at the car hoping it will fix the problem and instead spend a little time diagnosing it first. Life was a little easier when I was just a wrench.

Re: gauge silliness [Re: HealthServices] #665347 04/09/10 05:08 PM 04/09/10 05:08 PM
Joined: Sep 2007 Posts: 5,037 hi sharpie OP Moparts Linguist
sharpie OP Moparts Linguist Joined: Sep 2007 Posts: 5,037 hi	Quote: Quote: there's actually two separate grounds for the gauge panel. One is for all of the lights including the signals and hi-beam lights, the other is for all of the gauges. Each runs through the bulkhead and out to the chassis ground inside the engine bay on the wiper motor. So there is a ground from the battery to the chassis? Or how is the ground getting back to the battery [-]? Through the engine itself, I would think. Let me doublecheck my photos though.

Re: gauge silliness [Re: sharpie] #665348 04/09/10 05:11 PM 04/09/10 05:11 PM
Joined: Dec 2007 Posts: 7,759 So Cal HealthServices Why would you even post that?
HealthServices Why would you even post that? Joined: Dec 2007 Posts: 7,759 So Cal	Quote: Through the engine itself, I would think. Let me doublecheck my photos though. Hopefully not thru the motor mounts but thru a engine ground from the engine to the chassis. Allen Here's a novel idea, let's not throw a bunch of parts at the car hoping it will fix the problem and instead spend a little time diagnosing it first. Life was a little easier when I was just a wrench.

Re: gauge silliness [Re: HealthServices] #665349 04/09/10 05:12 PM 04/09/10 05:12 PM
Joined: Sep 2007 Posts: 5,037 hi sharpie OP Moparts Linguist
sharpie OP Moparts Linguist Joined: Sep 2007 Posts: 5,037 hi	Quote: Quote: Through the engine itself, I would think. Let me doublecheck my photos though. Hopefully not thru the motor mounts. why is that bad? the bolt touches each side, no?

Re: gauge silliness [Re: sharpie] #665350 04/09/10 05:17 PM 04/09/10 05:17 PM
Joined: Jan 2003 Posts: 32,947 Grand Prairie,Texas stumpy I Win
stumpy I Win Joined: Jan 2003 Posts: 32,947 Grand Prairie,Texas	Motor mounts are rubber and don't ground to the frame. You diffenately need a ground from the block to the body and to the frame. I have seen more than one throttle cable or shift cable burnt through because they became the only grounds to the engine and couldn't carry the amps from the starter draw etc.

Re: gauge silliness [Re: sharpie] #665351 04/09/10 05:23 PM 04/09/10 05:23 PM
Joined: Dec 2007 Posts: 7,759 So Cal HealthServices Why would you even post that?
HealthServices Why would you even post that? Joined: Dec 2007 Posts: 7,759 So Cal	Quote: Quote: Quote: Through the engine itself, I would think. Let me doublecheck my photos though. Hopefully not thru the motor mounts. why is that bad? the bolt touches each side, no? Not nearly enough. make sure you have both a engine ground from the engine to the chassis and a battery ground from the battery [-] to the chassis. You also have to have the engine ground but you already mentioned you have a battery [-] to the engine. Which is not enough by itself. Allen Here's a novel idea, let's not throw a bunch of parts at the car hoping it will fix the problem and instead spend a little time diagnosing it first. Life was a little easier when I was just a wrench.

Re: gauge silliness [Re: stumpy] #665352 04/09/10 05:33 PM 04/09/10 05:33 PM
Joined: Sep 2007 Posts: 5,037 hi sharpie OP Moparts Linguist
sharpie OP Moparts Linguist Joined: Sep 2007 Posts: 5,037 hi	Quote: Motor mounts are rubber and don't ground to the frame. You diffenately need a ground from the block to the body and to the frame. What I don't understand here is the car runs fine, charges fine, and even has voltage to spare. It's just the gauges.

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