The Ford Barn

Tony99 · 03-21-2026, 03:20 AM

Hi Ford barners,

I have a 51 Mercury with original 6 volt positive ground.
Has anyone installed an extra ground strap from engine to firewall to improve grounding and did it improve things like brighter lights etc. I have replaced the dash & engine harness

I noticed 49-51 Merc convertibles have strap 8A-14303 that mounts from fuel pump bracket bolt to firewall.

I went a bit overboard & used an early flathead strap from transmission/throttle control bracket as that looked to be a good earth point with 2 x 5/16 holes already there for a bolt & screwed other end to firewall.

PS This is my first post��

nelsb01 · 03-21-2026, 05:56 AM

While not a Mercury, my 1949 Ford Fordor Custom has a ground strap from the engine to the cowl.

40cpe · 03-21-2026, 07:37 AM

I think you would be better served to attach to a bolt directly on the engine instead of the throttle bracket.

Kens 36 · 03-21-2026, 09:25 AM

On 1949 Fords, the ground strap from the firewall to engine was standard. Starting in 1950, Ford only used the ground strap on convertibles. I'm not totally sure about Mercurys. However, it can't hurt. But, as stated above, it should be connected directly to the engine.

Ken

petehoovie · 03-21-2026, 09:54 AM

Quote:

Originally Posted by Tony99

Hi Ford barners,

I have a 51 Mercury with original 6 volt positive ground.
Has anyone installed an extra ground strap from engine to firewall to improve grounding and did it improve things like brighter lights etc. I have replaced the dash & engine harness

I noticed 49-51 Merc convertibles have strap 8A-14303 that mounts from fuel pump bracket bolt to firewall.

I went a bit overboard & used an early flathead strap from transmission/throttle control bracket as that looked to be a good earth point with 2 x 5/16 holes already there for a bolt & screwed other end to firewall.

PS This is my first post��

Tony99 · 03-21-2026, 10:30 AM

Sponsored Links (Register now to hide all advertisements)

Thankyou for the replies, I will look for an alternative mount bolt on engine for this

hueyhoolihan · 03-21-2026, 10:46 AM

IMO, it would only be necessary if the one you have is defective in some way, in which case i would replace it.

BTW, on my '41 ford 6v positive ground car, i replaced all the battery wires, ground wires AND the one that runs from the solenoid to the starter with #00 wires from here and cleaned and removed any paint and corrosion from all connections :

https://www.ebay.com/itm/196129030249

cranks over as well as any of my modern 12v w/alternator cars. but a car with a generator (if that's what you've got) will always perform poorly at idle and the headlights will dim. might want to check the starter button ground too, as it grounds using the body of the button to the dash and can become corroded and loose too. at least it did on my car.

47topless · 03-21-2026, 10:46 AM

Use an intake manifold bolt. Remove all paint at strap contact point.

rotorwrench · 03-21-2026, 12:41 PM

The early 6-volt voltage regulators were rubber mounted to the firewall and had a jumper to ground the case to the firewall. One of my 51 Merc cars is Banning blue on the lower body just like that. My two early 51 cars have a lot of grounding between the different drive train and body parts so I've never added any bonding straps and everything works OK. the battery is bonded to the engine and the engine is bonded through the mounting bolts & bushings. The rubber acts as a cushion but the bolts make physical contact. The generator is bolted on plus it's well connected to the VR so it bonds through as long as the VR is bolted to the firewall.

A lot depends on condition of all the interconnection points to electrical equipment. If a car has a lot of corrosion, it will get to be problematic at some point. Bonding jumpers are sort of a band aid to an underlying problem but I would never tell a person not to do it if it solves an immediate problem.

ScubaChief60 · 03-21-2026, 07:27 PM

Had to jump in here.

I put a new 350 V8 in my 1996 Tahoe a few years back ( I know this is a Ford Forum... but bear with me

). I had an immediate issue that when I drove the Tahoe far enough to get the engine hot... I then could not get it to restart until it had cooled down once more.

This happened to me in front of a NAPA store. One of the young men working in the NAPA store saw this old gray haired man ( that would be me

) with the hood up and so he came out to assist. Turns out that his dad was a retired GM Electrical Engineer and so he got him on the phone and advised him what was happening. Within 30 seconds the old engineer advised to check the engine block to frame grounding strap. It was the braided type and it was loose.

After tightening the strap the old gal fired right up.

The engineer went on to educate me as to what was really happening. He said that as the grounding strap got hot that the resistance increased making it useless in its oily and loose condition. When it was cold... it was marginally enough to work as intended.

He also advised loosing the braided type grounding strap and instead replacing it with a heavy gauge shielded wire just like the cable to the starter from the battery. This cable with its shielding/coating is less susceptible to getting oily and corroded he advised. Further more he even suggested adding a second engine block to frame ground cable somewhere in the vicinity of the starter, which I did.

Yes... it has been a few year now and that problem has been solved.

So... the takeaway here is that ground is definitely vital.

Pleas all weigh in here if I have missed the mark. I take no offense since teamwork is the way to the best outcome.

Tony99 · 03-22-2026, 01:22 AM

hello Huey, 51 Mercs don't have a specific earth strap from engine to firewall like the earlier cars. There is an earth strap from battery to engine, then from solenoid a heavy gauge wire like that link you have straight to the starter motor.
Like Rotor wrench mentions there is a lot of bonding already and my straps are correct size & in good shape. I was always a bit unsure as to how the engine bonded to the frame & firewall as it sits on rubber bushings but I guess there are the bolts of the water pumps to the frame which I assume then earths the firewall.
Seems like these cars have "switches" that earth to the metal rather than a seperate earth on the switch like the starter button & dome light switch & the courtesy light switches that press in as you close the door. I replaced my door switches with nos ones & then had an issue where the dash lights would stay on with door closed. Happened after a few months. I discovered that one of the switches wasn't making good contact on the door pillar as when I wiggled it lights would turn off & on. hence I thought an additional earth strap to firewall may fix a possible degraded earth?. I removed that door jamb switch since needless to say hard to remove without breaking it which I did so now will try with another switch. I did notice the replacement door pillar switches that have a plastic body have a 2 wire connector so one can be earthed to back of dash, rather than rely on the body of the switch making contact with the metal as an earth. As others have said proper ground is important.

Tony99 · 03-22-2026, 01:23 AM

Thanks everyone for tips

corvette8n · 03-23-2026, 07:07 AM

I spray my flat braided cables with fluid film before I install them this keeps them from corroding in my salt laden area.

chap52 · 03-23-2026, 07:32 AM

Never too many... We would always add an additional ground strap from a transmission cover bolt to the frame on our model A's. Chap

rotorwrench · 03-23-2026, 01:25 PM

The mid century Ford and Mercury cars had two terminals on the side of the generator (field & ground) and one on the back (armature). The power and ground wires are fairly large. The ground wire connects to the firewall on one of the voltage regulator bolts and has a jumper to the VR case , since the originals were rubber mounted for isolation. This grounding set up was the main connection between the engine/drive train and the body. These old cars only had a 35 amp system for the most part so this was considered sufficient by the FoMoCo engineers. I went back and looked at the three engine-transmission mounts and I was wrong about them having any bond with the frame. They are fully isolated so that generator to body wire is it. The body is attached to the frame enough to have bonding to the chassis even though it also has rubber mounts in a lot of areas. Engine and transmission electrics for overdrive cars all ground direct to the engine and battery. All of the lights and horn plus accessories ground through the body.

03-21-2026, 05:56 AM	#2
nelsb01 Senior Member Join Date: May 2010 Location: Up North Posts: 870	Re: Extra Ground Strap 51 Merc. Engine to firewall While not a Mercury, my 1949 Ford Fordor Custom has a ground strap from the engine to the cowl.

03-21-2026, 07:37 AM	#3
40cpe Senior Member Join Date: May 2010 Location: Star, MS Posts: 4,161	Re: Extra Ground Strap 51 Merc. Engine to firewall I think you would be better served to attach to a bolt directly on the engine instead of the throttle bracket.

03-21-2026, 09:25 AM	#4
Kens 36 Senior Member Join Date: May 2010 Location: Northern Illinois Posts: 571	Re: Extra Ground Strap 51 Merc. Engine to firewall On 1949 Fords, the ground strap from the firewall to engine was standard. Starting in 1950, Ford only used the ground strap on convertibles. I'm not totally sure about Mercurys. However, it can't hurt. But, as stated above, it should be connected directly to the engine. Ken __________________ https://www.nirgv8.org

03-21-2026, 10:30 AM	#6
Tony99 Junior Member Join Date: Jun 2021 Posts: 4	Re: Extra Ground Strap 51 Merc. Engine to firewall Sponsored Links (Register now to hide all advertisements) Thankyou for the replies, I will look for an alternative mount bolt on engine for this

03-21-2026, 10:46 AM	#7
hueyhoolihan Senior Member Join Date: Dec 2024 Location: central coast california Posts: 593	Re: Extra Ground Strap 51 Merc. Engine to firewall IMO, it would only be necessary if the one you have is defective in some way, in which case i would replace it. BTW, on my '41 ford 6v positive ground car, i replaced all the battery wires, ground wires AND the one that runs from the solenoid to the starter with #00 wires from here and cleaned and removed any paint and corrosion from all connections : https://www.ebay.com/itm/196129030249 cranks over as well as any of my modern 12v w/alternator cars. but a car with a generator (if that's what you've got) will always perform poorly at idle and the headlights will dim. might want to check the starter button ground too, as it grounds using the body of the button to the dash and can become corroded and loose too. at least it did on my car.

03-21-2026, 10:46 AM	#8
47topless Senior Member Join Date: Jun 2022 Location: Northern Colorado Posts: 496	Re: Extra Ground Strap 51 Merc. Engine to firewall Use an intake manifold bolt. Remove all paint at strap contact point.

03-21-2026, 12:41 PM	#9
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 18,006	Re: Extra Ground Strap 51 Merc. Engine to firewall The early 6-volt voltage regulators were rubber mounted to the firewall and had a jumper to ground the case to the firewall. One of my 51 Merc cars is Banning blue on the lower body just like that. My two early 51 cars have a lot of grounding between the different drive train and body parts so I've never added any bonding straps and everything works OK. the battery is bonded to the engine and the engine is bonded through the mounting bolts & bushings. The rubber acts as a cushion but the bolts make physical contact. The generator is bolted on plus it's well connected to the VR so it bonds through as long as the VR is bolted to the firewall. A lot depends on condition of all the interconnection points to electrical equipment. If a car has a lot of corrosion, it will get to be problematic at some point. Bonding jumpers are sort of a band aid to an underlying problem but I would never tell a person not to do it if it solves an immediate problem.

03-21-2026, 07:27 PM	#10
ScubaChief60 Senior Member Join Date: Mar 2023 Location: Summerfield, NC Posts: 256	Re: Extra Ground Strap 51 Merc. Engine to firewall Had to jump in here. I put a new 350 V8 in my 1996 Tahoe a few years back ( I know this is a Ford Forum... but bear with me ). I had an immediate issue that when I drove the Tahoe far enough to get the engine hot... I then could not get it to restart until it had cooled down once more. This happened to me in front of a NAPA store. One of the young men working in the NAPA store saw this old gray haired man ( that would be me ) with the hood up and so he came out to assist. Turns out that his dad was a retired GM Electrical Engineer and so he got him on the phone and advised him what was happening. Within 30 seconds the old engineer advised to check the engine block to frame grounding strap. It was the braided type and it was loose. After tightening the strap the old gal fired right up. The engineer went on to educate me as to what was really happening. He said that as the grounding strap got hot that the resistance increased making it useless in its oily and loose condition. When it was cold... it was marginally enough to work as intended. He also advised loosing the braided type grounding strap and instead replacing it with a heavy gauge shielded wire just like the cable to the starter from the battery. This cable with its shielding/coating is less susceptible to getting oily and corroded he advised. Further more he even suggested adding a second engine block to frame ground cable somewhere in the vicinity of the starter, which I did. Yes... it has been a few year now and that problem has been solved. So... the takeaway here is that ground is definitely vital. Pleas all weigh in here if I have missed the mark. I take no offense since teamwork is the way to the best outcome.

03-22-2026, 01:22 AM	#11
Tony99 Junior Member Join Date: Jun 2021 Posts: 4	Re: Extra Ground Strap 51 Merc. Engine to firewall hello Huey, 51 Mercs don't have a specific earth strap from engine to firewall like the earlier cars. There is an earth strap from battery to engine, then from solenoid a heavy gauge wire like that link you have straight to the starter motor. Like Rotor wrench mentions there is a lot of bonding already and my straps are correct size & in good shape. I was always a bit unsure as to how the engine bonded to the frame & firewall as it sits on rubber bushings but I guess there are the bolts of the water pumps to the frame which I assume then earths the firewall. Seems like these cars have "switches" that earth to the metal rather than a seperate earth on the switch like the starter button & dome light switch & the courtesy light switches that press in as you close the door. I replaced my door switches with nos ones & then had an issue where the dash lights would stay on with door closed. Happened after a few months. I discovered that one of the switches wasn't making good contact on the door pillar as when I wiggled it lights would turn off & on. hence I thought an additional earth strap to firewall may fix a possible degraded earth?. I removed that door jamb switch since needless to say hard to remove without breaking it which I did so now will try with another switch. I did notice the replacement door pillar switches that have a plastic body have a 2 wire connector so one can be earthed to back of dash, rather than rely on the body of the switch making contact with the metal as an earth. As others have said proper ground is important.

03-22-2026, 01:23 AM	#12
Tony99 Junior Member Join Date: Jun 2021 Posts: 4	Re: Extra Ground Strap 51 Merc. Engine to firewall Thanks everyone for tips

03-23-2026, 07:07 AM	#13
corvette8n Senior Member Join Date: Jul 2010 Location: 36 miles north of Albany NY Posts: 3,323	Re: Extra Ground Strap 51 Merc. Engine to firewall I spray my flat braided cables with fluid film before I install them this keeps them from corroding in my salt laden area.

03-23-2026, 07:32 AM	#14
chap52 Senior Member Join Date: Jun 2013 Location: Marana Arizona Posts: 1,869	Re: Extra Ground Strap 51 Merc. Engine to firewall Never too many... We would always add an additional ground strap from a transmission cover bolt to the frame on our model A's. Chap

03-23-2026, 01:25 PM	#15
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 18,006	Re: Extra Ground Strap 51 Merc. Engine to firewall The mid century Ford and Mercury cars had two terminals on the side of the generator (field & ground) and one on the back (armature). The power and ground wires are fairly large. The ground wire connects to the firewall on one of the voltage regulator bolts and has a jumper to the VR case , since the originals were rubber mounted for isolation. This grounding set up was the main connection between the engine/drive train and the body. These old cars only had a 35 amp system for the most part so this was considered sufficient by the FoMoCo engineers. I went back and looked at the three engine-transmission mounts and I was wrong about them having any bond with the frame. They are fully isolated so that generator to body wire is it. The body is attached to the frame enough to have bonding to the chassis even though it also has rubber mounts in a lot of areas. Engine and transmission electrics for overdrive cars all ground direct to the engine and battery. All of the lights and horn plus accessories ground through the body.