North American Turbocoupe Organization



Ground wire question
John B Offline
Member
#1
With the battery relocated in the trunk, I want to eliminate the negative battery cable in the engine bay. The ground wire to the engine block (driver side) is also corroded so I want to replace it. Currently, the ground from the engine runs to the negative battery cable terminal (2 or 4 ga wire). The terminal also has one smaller wire (maybe a 10ga wire) that runs and eventually splits into three wires: one going to the driver side fender ground location and the other two running to a plug (I believe this is the ECU ground). Does it matter what size ground is ran to the engine? I would like to cut the smaller 10ga wire from the terminal and solder on an eyelet and attach that to the engine block. This would eliminate the larger, corroded negative battery cable and battery terminal. Please let me know your thoughts for the best approach here.
88 Turbo Coupe: Front mount intercooler, MGW short throw shifter, full coilover conversion, tubular control arms front and rear, svo front brakes, vacuum assist brake swap, manual steering swap, GT35R turbo with external gate, pimpx ecu, 60lb injectors, 3 core aluminum radiator, Boport 1.5 cam, gutted upper, corbeau fixed back seats, and the list goes on.
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Jeff K Offline
Administrator
#2
Yes, those 2 wires are for the ECU ground (ECM pins 40 and 60).

Your plan sounds good to me.
Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 24 psi, forced air IC, water injection, BPV, Ranger cam, subframes, etc., etc.
86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP N2O, ignition, gears, suspension, etc., etc.
05 Taurus SEL Duratec daily driver
04 Taurus Duratec (wifes car)
02 Pontiac Grand Prix GT
95 Taurus GL Vulcan winter beater
67 Honda 450 Super Sport - completely customized
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John B Offline
Member
#3
Excellent, thank you Jeff. I haven't had a chance to look yet but is there an engine ground on the passenger side of the block?
88 Turbo Coupe: Front mount intercooler, MGW short throw shifter, full coilover conversion, tubular control arms front and rear, svo front brakes, vacuum assist brake swap, manual steering swap, GT35R turbo with external gate, pimpx ecu, 60lb injectors, 3 core aluminum radiator, Boport 1.5 cam, gutted upper, corbeau fixed back seats, and the list goes on.
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BradM Offline
Member
#4
There is a ground wire on the back of the block, drivers side. It's attached via a bell housing bolt. I found no ground wire on the passenger side block but there is a ground wire going to the stock turbo.
1965 Mercury Comet Caliente; 1968 Mercury Monterey; 1969 F100 Ranger; 1987 Thunderbird Turbo Coupe
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John B Offline
Member
#5
Thank you for the confirmation Brad. I have to take a look later. I’ve had an aftermarket turbo on there for a few years now and I’m not sure what I did with the turbo ground wire. I’ll also look for the one on the back of the block.

I finished making the ground wires yesterday where the negative battery cable use to be. The wire going from the block to the battery terminal was corroded and so were the two wires for the ECU ground at the plug where they eventually combine into one wire.

I cut all three of those wires back to points that weren’t corroded. The two ECU ground wires were combined and then soldered to a new wire that runs to the fender ground. The third gray wire was also soldered to a new wire and runs to the fender ground. Lastly, there’s a new ground cable that runs from the fender to the engine block. Pretty nice to clean these up and have new wire in there
88 Turbo Coupe: Front mount intercooler, MGW short throw shifter, full coilover conversion, tubular control arms front and rear, svo front brakes, vacuum assist brake swap, manual steering swap, GT35R turbo with external gate, pimpx ecu, 60lb injectors, 3 core aluminum radiator, Boport 1.5 cam, gutted upper, corbeau fixed back seats, and the list goes on.
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Jeff K Offline
Administrator
#6
In a stock application the orange ground wire that goes to the turbo is important. That wire is the O2 sensor ground reference. if not connected to a good solid ground, the PCM will not be getting the correct voltage signal. If you have an aftermarket PCM (Pimp, etc) it may not be necessary.
Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 24 psi, forced air IC, water injection, BPV, Ranger cam, subframes, etc., etc.
86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP N2O, ignition, gears, suspension, etc., etc.
05 Taurus SEL Duratec daily driver
04 Taurus Duratec (wifes car)
02 Pontiac Grand Prix GT
95 Taurus GL Vulcan winter beater
67 Honda 450 Super Sport - completely customized
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John B Offline
Member
#7
If my memory is correct, that is the case when installing the Pimp ECU. When I installed mine years ago, you had to cut and slice into the harness for the wideband O2 sensor and I don't believe that orange ground wire is needed. I'd have to check the Pimp installation instructions to confirm 100% though
88 Turbo Coupe: Front mount intercooler, MGW short throw shifter, full coilover conversion, tubular control arms front and rear, svo front brakes, vacuum assist brake swap, manual steering swap, GT35R turbo with external gate, pimpx ecu, 60lb injectors, 3 core aluminum radiator, Boport 1.5 cam, gutted upper, corbeau fixed back seats, and the list goes on.
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