I've been going through my electrical system and learning as I go so bear with me. I have a modded S5 alternator, Optima Yellow Top. I've replaced the battery (+) alternator and starter with 4ga cable, cable to main (engine bay) fuse box is 8ga. I have replaced OEM grounds with a single 4ga going to OEM location at driver shock tower. I have a second 4ga going from same location to starter through bolt. I also have a 4ga from top of engine keg to firewall. I have a Taurus efan wired in with a Starion temp switch going through a relay with a manual override switch in the cockpit of the car. I have an aftermarket stereo and amps which are currently disconnected from power. I have 4 aftermarket gauges: AEM boost gauge, Innovate wideband, Prosport water and oil temp gauges. I also have an old Clifford alarm which is currently disconnected.

I previously had a draining battery which turned out to be a faulty modded S5 alt (130amps). The shop that modded it replaced it for free and the battery drain is fixed.

Now I'm tracking down other electrical problems which some of them I think are ground loop problems.

1. My AEM boost gauge will sporadically start reading all over the place. Sometimes it idles lower inHG than it should be and sometimes way, way high. I have seen it at idle reading 20psi. It functions as it should, will range up and down with vacuum and boost, but it's zero point is way way off at times. I've tried allowing the gauge to do proper opening and closing ceremonies before turning the engine over and off with no change.
   
2. Also I've seen my Prosport water temp gauge read off. It will at times not go to zero when I turn the engine off and remove the key. When I come back to the car it's still reading whatever temp I parked the car at. When I start up the engine it will continue to read that same temp...but will slowly lower and lower and lower till I assume it's reading accurately. It seems that once the coolant temps and gauge temps meet it is then reading accurately. I can turn my fan on and off and watch the temps on the gauge rise and fall.
   
3. My aftermarket alarm was acting very odd and I removed the alarm CPU and removed the fused power from the battery terminal. Problem was that the alarm siren was going off after I pulled the fuse out and nothing should have been getting power. It was a while ago that it did this, so I don't remember the exact events.
   
4. Possibly related, or possibly not. My OEM volt meter still shows sporadic charging. I'll at times come out to my car while running errands. Start up the engine and the volt meter will show barely over 12v or some range under 14v it should show at charging. I'll raise my RPMs and won't see the normal jump from under 14v to 14v that happens when the engine is at 1k or so RPMs. As I'm driving the volt meter will slowly rise and show what I assume are correct readings. I realize the OEM gauges aren't the most reliable and am willing to write this one off as a failing/inaccurate gauge. But at the same time it could be indicative of a problem.
   
5. Also possibly unrelated but still electrical. My rear defrost does not work. The button lights up but I get no heat on the rear window. I've checked fuses. I checked for voltage on the two wires on the window and get no voltage. I tried swapping a different and presumably working switch and no change.

Last night I went through most of my grounds with my DMM, cleaned up my grounds and consolidated my grounds on as few spots as possible.

1. Engine to firewall read 2.1 ohms so I left it be.
2. Prosport temp sender ground on passenger shocktower showed O.L. so I moved it to driver shocktower. Also I noticed the ground wire insulation had split right as it came off the sender so I covered it with RTV.
3. Driver shocktower read 2.2 ohms but I sanded it down more and sprayed it with aeresol electrical grease (can't remember the name of the stuff). I consolidated most all my grounds here. Taurus efan, alarm siren, oil temp sender, water temp sender, oil pressure sender (IIRC, though I'm not currently using the oil pressure gauge because I don't have a spot available to mount the gauge). After cleaning it up it had 1.5 ohm resistance.
4. Starter through bolt had 2.2 ohm resistance and I left it alone.

In the cockpit of the car

1. high on driver kickpanel I cleaned up that ground and it read 1.5 ohms. At that spot I have a small OEM ground (not sure what it grounds) on what looks like a 20ga wire. I have grounds for my alarm, cpu ground and grounds for door actuators.
2. lower on the driver kickpanel I cleaned up that ground and it also read 1.5 ohms. At that spot I grounded Taurus efan manual override switch (it's not full manual, i have it wired into a temp switch), AEM boost, Innovate wideband, Prosport water and oil temp gauges, aftermarket stereo, and grounds for power antenna relay.
   
3. It got late and I did not check these, but I did the grounding mod for the ECU a while back. I have consolidated grounds for the ECU going to either passenger kick panel or one of the ECU mount bolts...I don't remember which.
   
4. I also did not check aftermarket stereo amp ground, but I don't have any power going to the amps. Until I work out the general function electrical I could careless if I have music. The 4ga power to the amps is disconnected from the battery.

Here is something odd I noticed yesterday while working. I was getting sparks on some of my grounds to the chassis of the car. The driver shocktower was sparking enough that I disconnected the positive battery terminal. I reconnected the battery terminals and was buttoning things up. I realized I had not reconnected the open door switch. As I was screwing that down to the body I saw little tiny sparks on that screw. That doesn't seem very normal to me, but I'm new enough that I'm tossing it out there as a possible symptom to my electrical problems.

I took the car for a drive after redoing my grounds and at first it was smooth sailing. Boost gauge was reading correctly, fan was coming on properly, water temp gauge was working properly. I started the engine up and turned it off multiple times before I left to test the boost gauge. I toggled the efan on and let it run some and no blown fuses.

BUT I make a stop along the way. Start up the engine and the boost gauge is reading under what it should be. It was zeroing out after opening ceremony at about 7inHG and would operate seemingly properly with that as it's zero point. At that point it was getting late and I haven't touched the car since.

Suggestions and thoughts are greatly appreciated. These electrical problems are tops on my to do list and would love to get this frustration off my list. Before I started addressing the ground loop I had a friend suggest I add a grounding strap from the chassis of the car to the frame...anyone have thoughts on that specifically or any other advice?

 

How are you measuring your grounds. Thats alot of resistance to be nothing more then a ground wire. Ideally on a ground you want under 1.0 ohm. I prefer even less .5 ohm of resistance, anything more is considered excessive. On modern cars they say .2 ohms loss across each connection in a circuit is acceptable.

 

You can't ground from the body to frame because the rx7 is a unibody and has no frame. You should have a body to engine ground though. Check for ground loops by using a DVM on DC settings and look for voltage across opposite sides of the cars chassis. Does it just spark once? Or every time. Could be a cap somewhere discharging. Like in the radio for instance.

 

I made a 14 gauge or so wire and crimped an alligator clip to it. I clip onto the battery neg post. I have my DMM set to autoranging resistance. I plug a lead with an alligator clip and clip that on the wire clipped onto the neg battery terminal. I sanded the paint off the ground point and sprayed with electrical lubricant. Most of the grounds I tested on bare metal as a reference and then tested again once the ring terminals were bolted down. I used the unused lead on the DMM I touched to the ground point. I saw the same readings on the bare metal as the bolt head after it was bolted down. I don't remember the DMM reading mOhms, but I can recheck them, maybe tomorrow after work.

The 4ga grounding cables I made should be pretty solid. I took copper ring terminals, heated them with a MAP torch till solder would melt in them and set the exposed copper in. A little shrink tubing and they were done.

I'm not following you on voltage across opposite sides of the car chassis. I thought to ensure you didn't have ground loops you wanted to check you grounds and make sure they were all similar resistance. I'm not familiar with using DC voltage to do the same thing. I just bought a new Fieldpiece that's pretty nice and true RMS and I'm waiting for the AC/DC amp clamp to arrive..it had to be special ordered. Now I just need to learn how to use it. I'll Google some tonight about using voltage to find ground loops.

About the spark, it was both the driver side shock tower ground that was sparking most every time I worked the bolt off ring terminals. The door switch was a little arc every time I touched the screw to the screw hole. It was small and if I hadn't been looking for it I would not have seen it.

 

Not sure if it helps, but w/the meter set to DC volts and key to on the ground wires should have 0 volts (Red meter lead to the ground wire and the Black meter lead to the engine block). How are you grounding the gauges which you are having problems with? Are they sharing the same ground or different?

 

So put the DMM in series with the ground wire I'm testing, got it.

The gauges are sharing the same ground.

 

Your measuring through the battery then.

What you want to measure is from the point on the block or transmission to the point on the body that it connects to. This will give you your proper resistance of your ground circuit. You want to reading in parallel. Example, put your DMM positive lead on the starter bolt that has the ground, take the negative lead and put it where it connects, be it the battery or the body and measure the resistance. Do this over every ground wire, if your higher then say .5 ohms I would question your DMM or your ground. Verify how much resistance your leads have in them by connecting the DMM positive to the Negative directly. If you DMM shows an resistance of .2 ohms factor that into your measurements so say if your measure meant was .6 ohms, your resistance in that circuit is really .4 because your test leads have .2 ohms resistance through them and the DMM

 

Dont forget about potential difference, also known as voltage.

The best way to measure for ground loops is to measure voltage between two grounding points. For example, you could measure the voltage between an amplifier terminal and its grounding point. It's a short cable, so you should see 0.0v or possibly 0.1v if the cable is poorly grounded.

The hard thing about ground loops, without getting too technical, is the resistance of positive and negative wires. Alarms and amplifiers are REALLY prone to this issue, more so with alarms. I know you have disconnected positive from these items on your car, but you need to disconnect them from ground also to keep them from being a backfeed on the grounding system. Yes, they can back feed a ground even when they aren't connected.

Since a car is not earth grounded (i.e a giant infinite ground) you are inevitably going to have very minor ground looping occurring. The key is to minimize it. I work in the 12 volt industry and have to deal with this demon on a regular basis.

From my experience, the best and fastest way to solve a ground loop problem is to evaluate, isolate, or eliminate. The more ground points you have, the worse off you are. The more ground points connected to each other, with a voltage difference, the worse off you are. Using separate ground points isn't all that bad, but unless you know exactly what your doing, it can cause an issue thus why I will tell you the super easy but not so good method...

Ground it and test...voltage across ground unacceptable...try another spot and test again.

Voltage difference between the battery terminal and a grounding point on the chassis should not be over 0.2 volts. Anything over that means you are looping somewhere.

I know it's a long post but I suggest reading it, and if you want anything more specific on the issue, you can always PM me.

 

Ah, so I'm not disconnecting the ground and putting the DMM leads between the ground wire and the ground point.

Disconnecting the amp grounds rather than power makes perfect sense now that you explain it. Same idea as disconnecting the battery ground.

Thanks for the advice everyone.

 

Just remember that all of your power is coming from ground (on an rx7 and most vehicles). Electrons are negative and they are flowing opposite of what you may think.

 

Coincedental to this thread I created, and my general electrical problems with my rebuild. I am taking classes (midlife crisis career change) for a different career path. This semester it's Electrical Circuitry and Progammable Logic Controls II. I do work with some electrical in the field, but it's mostly high voltage disconnects and basic low voltage control wiring. Most of the low voltage wiring is simply copying what the previous person did, or following basic diagrams.

 

Very curious finding. I believe I have fried stereo components but seem to have found the loop in one of the amp grounds. I have 3 amps: JL Audio for my sub, a very old Zapco (Probably 15 or more years old) for my components, and an Alpine that I inherited with my previous convertible for the speakers behind convertible seats.

The Alpine ground wasn't very good...or rather the grounding cable was junk. It was an old one that I slapped on there without much care cause the amp wasn't all that important to me. If I have some fill sound coming from a cheap amp didn't really matter to me.

I had another more curious thing with my stereo. I turned it on so that the amps had voltage so I could check the grounds. I had no sound on the passenger side door components and no sub. The Zapco worked fine on the driver side. The JL for the sub wasn't turning on or wasn't getting power. I pulled the stereo out to see if I had pulled RCAs out while mucking around with the gauges and they were good. At that point I simply removed the grounds for the JL and Zapco. I'm unconcerned if I have tunes until I get more important things off the "to do" list.

I seem to have cured the boost gauge. It zeroes out find. I turned the engine over let it idle turned the engine off. Gauge still zeroes just fine.

Sorry for the long post, but here's the most curious part. I turn the stereo on just cause and I'm getting sound out of the speakers powered by the Alpine. I get out and check the ground wire thinking that maybe it's sitting on metal and grounding and it's not. I disconnected the power cable at the battery and pulled the harness from the back of the head unit.

 

Your last paragraph is a GREAT example of backfeed. The amp was working because it was grounding through the radio using the rca's ground shield. Your lucky you didnt fry the radio or melt the rca cables.

Pro tip: Always disconnect amplifier rca's before power and ground.

 

Good to know and I hope people learn from my mistakes. I am certainly not one of those forum members who only posts their success and brilliance. I do many things well, but some things I'm learning as I go.

Now on to other things....Gotta work out my Taurus efan. If it's not grounded to the battery it throws it's resetting breaker. It's a junkyard find and if I can't figure out how to test it I'll simply head to the junkyard and get another. I'll create a new thread for that if I struggle with it.