How to Properly Ground a Race Car

Bobby Fazio · 10-18-2015, 11:37 AM

I have been reading alot about this topic and want to avoid any ground loops if possible. The problem with my car is it still has tons of factory wiring in it so it's a big mess. .

I have a big 0 gauge wire going from BATT- right to the inside fender (wire brushed and bolted, grounding the chassis. I have 2 or 4 gauge wire coming off battery negative going to engine block. Actually I think it is the cam cover but whatever it is, it's the factory spot on the Mustang 5.0. I have a thin strap going from driver side cylinder head to firewall. I don't have a strap on passenger head but the alternator mounting includes block and head on that side so I figure it should be ok.

So what do you ground to where? I don't understand when it is best to ground to chassis, engine, cylinder head, or straight to battery negative. And why would it matter if you ground two things to the same chassis ground, rather than grounding them to two different spots on the chassis? They all return through the chassis back to the BATT-

Signman · 10-18-2015, 03:39 PM

With EFI ground reference for each sensor should be relative to it's location due to possible voltage flowing through the ground circuit from leakage of other systems same for data logging sensors they are looking for 0-5 volt input; slight variation can mean a lot..
Bad grounds show up as erratic sensor data also look for electrical noise which can influence wiring not shielded.
Shielded wiring should always be grounded to the chassis to battery. Don't depend on engine and chassis bolts without checking with a meter, gaskets and other products can act as an electrical insulator.

FireSale · 10-18-2015, 03:41 PM

Ground to multiple points just in case one of them gets corroded, loose or whatever.

My 68 Mustang (my avatar) is street legal so it's full of extra wiring. My one wire alternator is grounded directly back to the battery in the trunk with 10 gauge wire. The battery negatives are grounded to tabs welded to the rear angle bars for the cage, one on each side.

Over the Winter I'm going to weld tabs to the stock frame in the engine compartment while it's empty and do away with any firewall or fender well ground wires.

I have a Painless Performance street strip wiring kit that includes a fuse block for street functions and a switch panel for race functions. I added a Bussman 12 circuit fuse box for all the extra gauges and stuff I have added. This made a rats nest of wiring under my dash so I just now redid it into a consolidated panel on pegboard under an aluminum cover where it's easy to get at. It's grounded to a tab welded to the 6X6 plate that the front of my cage anchors to.

It's all buttoned up right now, but I can take the covers off and post photos tomorrow if you want to see how I tried to tame this stuff.

Dale

Ed Wright · 10-18-2015, 05:15 PM

My rear mounted batteries' ground cable goes up to a stud on the rear of the passenger side cylinder head, same stud had all other grounds. Body is grounded directly to the engine as well. Ditto the MSD. No issues.

west coast · 10-19-2015, 08:26 AM

The computer wires for ground need to go all the way to neg- right to the battery post. When i did this last year to my car it totally change my tune up. I had all ground coming together on a post insulator then a battery cable to the battery, computer was getting noise in that short run from fans and water pump. Bobby what efi are you running.

Bobby Fazio · 10-19-2015, 09:50 AM

Quote:

Originally Posted by west coast

The computer wires for ground need to go all the way to neg- right to the battery post. When i did this last year to my car it totally change my tune up. I had all ground coming together on a post insulator then a battery cable to the battery, computer was getting noise in that short run from fans and water pump. Bobby what efi are you running.

Fast XFI 2.0, I always wire computer to battery. However, other things like water pump, innovate O2 logger, distributor Hall effect sensor grounds, etc are all chassis or engine grounds.

buzzinhalfdozen · 10-19-2015, 10:43 AM

Bobby, don't have a fast system but B+ and B- both need to be directly to the battery for the ECU. Most of the systems I've seen as far as sensors go the ECU has discreet circuits for them ( the reference, low reference (ground) and signal all go back to the ECU, then use the main ECU ground which should be hooked directly to the battery. Most agree that any other inputs....O2's input signals (cam sync, crank sensor if it's a hall effect ) should share the ground that the ECU uses to eliminate ground offsets. All other things Alt. electric water pumps, fans ect. can be chassis grounded provided the engine AND chassis are properly grounded. I like to run a ground between cylinder heads and to chassis just to provide a solid ground path. To me the bottom line is to try and keep EFI componemts grounds seperated from everything else...by grounding the ECU directly to the battery you do just that.

Jeff Niceswanger · 10-20-2015, 06:36 AM

Don't go directly to battery on the positive side if your running 16 volt battery's . You will have to connect to kill switch, so you are not charging your ECU and MSD during charging . They charge at 20 volts ,and I found out the hard way it will pretty much damage everything in your car ......

k.pascoe · 10-20-2015, 12:12 PM

Remember any module or ecu needs to have electronic power and ground. That means power and ground must come from the battery directly. You can run electronic power and ground studs in the engine bay just run cables to them from the battery. (if truck mounted).

rallye bob · 10-21-2015, 08:03 AM

Dale Shearon..... Would love to see pic's of what you did...........

10-18-2015, 11:37 AM	#1
Bobby Fazio VIP Member Join Date: Nov 2009 Location: Egg Harbor Township, NJ Posts: 1,468 Likes: 1,448 Liked 4,365 Times in 501 Posts	How to Properly Ground a Race Car I have been reading alot about this topic and want to avoid any ground loops if possible. The problem with my car is it still has tons of factory wiring in it so it's a big mess. . I have a big 0 gauge wire going from BATT- right to the inside fender (wire brushed and bolted, grounding the chassis. I have 2 or 4 gauge wire coming off battery negative going to engine block. Actually I think it is the cam cover but whatever it is, it's the factory spot on the Mustang 5.0. I have a thin strap going from driver side cylinder head to firewall. I don't have a strap on passenger head but the alternator mounting includes block and head on that side so I figure it should be ok. So what do you ground to where? I don't understand when it is best to ground to chassis, engine, cylinder head, or straight to battery negative. And why would it matter if you ground two things to the same chassis ground, rather than grounding them to two different spots on the chassis? They all return through the chassis back to the BATT- __________________ '65 Mustang SS/L & L/SA DriverInterviews.com \| App.DragInsights.com

10-18-2015, 03:39 PM	#2
Signman Senior Member Join Date: Oct 2003 Location: Lower Slower Delaware Posts: 535 Likes: 22 Liked 269 Times in 99 Posts	Re: How to Properly Ground a Race Car With EFI ground reference for each sensor should be relative to it's location due to possible voltage flowing through the ground circuit from leakage of other systems same for data logging sensors they are looking for 0-5 volt input; slight variation can mean a lot.. Bad grounds show up as erratic sensor data also look for electrical noise which can influence wiring not shielded. Shielded wiring should always be grounded to the chassis to battery. Don't depend on engine and chassis bolts without checking with a meter, gaskets and other products can act as an electrical insulator. __________________ Frank Ferrucci I/SA 1271 "Be Thankful for the Gifts You are Given"

10-18-2015, 03:41 PM	#3
FireSale VIP Member Join Date: Feb 2014 Location: Lakewood Washington Posts: 1,407 Likes: 29 Liked 237 Times in 126 Posts	Re: How to Properly Ground a Race Car Ground to multiple points just in case one of them gets corroded, loose or whatever. My 68 Mustang (my avatar) is street legal so it's full of extra wiring. My one wire alternator is grounded directly back to the battery in the trunk with 10 gauge wire. The battery negatives are grounded to tabs welded to the rear angle bars for the cage, one on each side. Over the Winter I'm going to weld tabs to the stock frame in the engine compartment while it's empty and do away with any firewall or fender well ground wires. I have a Painless Performance street strip wiring kit that includes a fuse block for street functions and a switch panel for race functions. I added a Bussman 12 circuit fuse box for all the extra gauges and stuff I have added. This made a rats nest of wiring under my dash so I just now redid it into a consolidated panel on pegboard under an aluminum cover where it's easy to get at. It's grounded to a tab welded to the 6X6 plate that the front of my cage anchors to. It's all buttoned up right now, but I can take the covers off and post photos tomorrow if you want to see how I tried to tame this stuff. Dale __________________ Dale Shearon 68 Mustang 6394

10-18-2015, 05:15 PM	#4
Ed Wright Veteran Member Join Date: Mar 2005 Location: Sand Springs, OK Posts: 8,132 Likes: 896 Liked 390 Times in 170 Posts	Re: How to Properly Ground a Race Car My rear mounted batteries' ground cable goes up to a stud on the rear of the passenger side cylinder head, same stud had all other grounds. Body is grounded directly to the engine as well. Ditto the MSD. No issues. __________________ Ed Wright 4156 SS/JA

10-19-2015, 08:26 AM	#5
west coast Senior Member Join Date: Dec 2008 Location: Rainy Washington Posts: 609 Likes: 12 Liked 223 Times in 73 Posts	Re: How to Properly Ground a Race Car The computer wires for ground need to go all the way to neg- right to the battery post. When i did this last year to my car it totally change my tune up. I had all ground coming together on a post insulator then a battery cable to the battery, computer was getting noise in that short run from fans and water pump. Bobby what efi are you running. __________________ James Boyce 6052 K/SA Stock National record holder 2015,2018,2 times in 2022,2023

10-19-2015, 10:43 AM	#7
buzzinhalfdozen Senior Member Join Date: Sep 2006 Location: Bellevue Ohio Posts: 984 Likes: 0 Liked 11 Times in 8 Posts	Re: How to Properly Ground a Race Car Bobby, don't have a fast system but B+ and B- both need to be directly to the battery for the ECU. Most of the systems I've seen as far as sensors go the ECU has discreet circuits for them ( the reference, low reference (ground) and signal all go back to the ECU, then use the main ECU ground which should be hooked directly to the battery. Most agree that any other inputs....O2's input signals (cam sync, crank sensor if it's a hall effect ) should share the ground that the ECU uses to eliminate ground offsets. All other things Alt. electric water pumps, fans ect. can be chassis grounded provided the engine AND chassis are properly grounded. I like to run a ground between cylinder heads and to chassis just to provide a solid ground path. To me the bottom line is to try and keep EFI componemts grounds seperated from everything else...by grounding the ECU directly to the battery you do just that. __________________ Joe Buchanan SS/BX 3117

10-20-2015, 06:36 AM	#8
Jeff Niceswanger Senior Member Join Date: Jul 2003 Posts: 894 Likes: 684 Liked 1,031 Times in 368 Posts	Re: How to Properly Ground a Race Car Don't go directly to battery on the positive side if your running 16 volt battery's . You will have to connect to kill switch, so you are not charging your ECU and MSD during charging . They charge at 20 volts ,and I found out the hard way it will pretty much damage everything in your car ...... __________________ Jeff Niceswanger 3740 SS

10-20-2015, 12:12 PM	#9
k.pascoe Member Join Date: Aug 2008 Location: Fenton, Missouri Posts: 107 Likes: 0 Liked 0 Times in 0 Posts	Re: How to Properly Ground a Race Car Remember any module or ecu needs to have electronic power and ground. That means power and ground must come from the battery directly. You can run electronic power and ground studs in the engine bay just run cables to them from the battery. (if truck mounted).

10-21-2015, 08:03 AM	#10
rallye bob Member Join Date: Sep 2006 Location: Genoa, Illinois Posts: 489 Likes: 9 Liked 6 Times in 4 Posts	Re: How to Properly Ground a Race Car Dale Shearon..... Would love to see pic's of what you did...........