Brand new ground strap, installed clean and brushed on both transmission and body. Completely failed me. Wire brushed the neg to body. Checked the cables and replaced the post to starter cable (it was questionable ). Car still wouldn't turn over. Added a new 6 gauge cable from the negative terminal to the spot where the coil attaches to the tin work, turns over like a new car. Even my gauges are working better. Wth. Could it just be the transmission case itself?

I remember an argument about additional ground straps a couple years ago, but can't find it. Any reason not to just keep my aftermarket ground strap?

50 years of corrosion

It doesn't take much, but glad you found the fix

Corrosion where? I put a brand new strap on when I rebuilt the engine last year. Cleaned everything when the engine was out... Maybe the 50 year old metal (what's left on my car) just can't take it?

Corrosion on the unit body and between the panels
Not getting a good ground at your chassis mount likely

LOL... Funny how it's three Upstate NY guys here at the top talking about this first.

It must be the winter salt in the air that gets to our cars..

Ok, seriously now. When I redid my brothers wiring on his 6 conversion I ran a new ground wire anywhere that I could. I would say the best one was from the battery neg to the drivers side ground wire portion. You know the one next to the relay board. has a bunch of grounds to chassis. Then all new ground straps from chassis to trans, battery to chassis, and IIRC I ran a new ground to the front truck to help with the new fuse panel that I install there. His car never had an issue. Lights on gauges, and headlights are bright as can be. Try running a wire from the battery to the relay board side and see how that goes. I can go look and see what size I used if need be.

Thanks for the post! I would be interested to find out what size wire you used.

Measure where it’s at. I keep posting how to do this but no one takes it seriously.

Stop guessing

https://www.fenderbender.com/running-a-shop...ircuits-part-11

If you’re unclear on how to do this I’ll gladly help.

I was measuring and it all looks good till you hit the key. My eyes glaze over when superhawk starts writing about all the ways you measure load. I had my Porsche guy use his magic amp measuring device. Not like I was throwing parts at it, just pissed a brand new strap on perfectly clean points didn't work for more than a year. And it's parked all salt season, so seriously, in the air apparently.

Another interesting outcome: I updated to all LED lights and my fog lamps (not led) kept on working. After I fixed the ground today... No more fog lamps.

I used a 6 gauge lawn tractor battery cable.

It's the freedom that comes from the chalon lifestyle.

You cannot measure the resistance. Hundredths of an ohm matter.

Please read link. Have to measure voltage drop while cranking.

"while cranking" is the key phrase here. When everything is at rest or near rest, the current path works, add a real load and

I know, I actually do read your posts, but I went for amps instead. Neat tool.

So to answer your original question, I would not depend on grounding through the engine tin as a long term fix.

Last time I dealt with this I ran a new cable from the ground post to the upper bolt on the starter…that made it stfu and work.

Rich

Soooooooo.....coil mounted to the tin. That's a solid grounding point.

Thought that also but I'm too polite ...anyway better to use one of the air pump mounting bosses on the fan housing or similar 8mm on there, much better ,cheers.

Although I’m not a fan of multiple ground straps, Rich’s suggested location is a good one.

There are engineering design principles that guide where grounds are placed.

The main ground strap needs to be close to the starter. The starter is by far the largest current load in the vehicle. A starter is capable of drawing hundreds of amps. This is why the OEM ground strap goes to the transmission casting rather than the engine case.

You don’t want that starter ground having to be pulled though a fan shroud, through the engine case (potentially through bearings), and finally through to the transmission housing that the starter is attached to.

Other important design principles:

1) Braided ground strap can handle more current than an equivalent gauge stranded ground cable.

2) Ground straps are to be kept as short as possible to minimize voltage drop.

Ideally the OEM ground strap would go from the chassis / trunk area near the starter to the bolt Rich mentions. Post too long already without going into speculation on why they didn’t put it there.

Interesting, so the same stock place on the body, but to the starter bolt rather than the transmission case? That would imply the case is the issue?

Yeah, the tin doesn't make me comfortable either but it was convenient and apparently a way way better ground than a new strap on the transmission.

I might run a beefy cable from the battery post to the upper starter bolt in the engine compartment.

Not so sure I buy welding bearings and such, do transmission gears weld together because the case is the original ground? Now, using my oil pressure line as a route to ground, I worry about (copper).

I have an additional ground strap that goes from an alternator case bolt through a stout cable to the driver side ground stud. It helps! I was getting voltage drop through the doghouse - just enough to keep the battery from fully charging. You could not measure the drop at all when the car was off. When running, you could measure a 1.5 volt drop. Added the ground and the issue went away.

When I changed engines I kept the added ground cable.

Zach

Not highly likely but it all depends where the ground strap is, where electrons flow to, and how much current is drawn.

Around and find out.

https://www.waukbearing.com/en/resources/be...al-pitting.html

I to ran a ground strap from the alternator to the driver side ground in the engine compartment.

If you actually fastened the ground cable to the sheet metal engine ducting, then that is a bad thing, and could lead to the fasteners welding to the engine case.
Better is to use the fan shroud as a grounding point, and here is an ideal location.Click to view attachment
The alternator grounds to the fan shroud as well. You could add another ground wire from this point to the chassis ground stud near the relay panel. The starter (draws the most current of any device in the car) grounds to the trans case, and subsequently through the engine case to the fan shroud. Thus you have most of the important grounds tied together closely through the best conductors.
I have also had the same problem, as you did, with the battery ground stud not doing it's job. I am afraid that the 50 year old body is just not up to carrying the current that it is tasked with. No matter that the battery ground stud and the transmission ground stud are solid and clean, this does not seem to be enough anymore.

Interesting. My mustangs ground strap is on the block. Never heard of electrical pitting in 75 years of mustangs + their relatives.

Those are turbines and electrical generators.

That looks like a great place. I will see if it is on my shroud.

years ago I forgot to connect the trans ground strap when I was in too much of a hurry as a young PUNK doing a record setting clutch replacement. When the engine turned over slowly, I thought the battery weak, so connected a heavy duty charger. Next thing I see is smoke coming from between the seats. I melted the accelerator cable in the tunnel as the starter used the accelerator cable as the ground. I spend the whole weekeng cutting out the tube and replacing it!

I’m not saying it’s highly likely just that it’s a possibility with a split case if you were to ground on one side of the case and then pull several hundred amps across the case / bearing / crank interface should that become a path of least resistance

Do what makes you feel good.

I see. I moved it to that spot on the shroud. All good. Much more comfortable with that spot.

regarding the grounding "strap" you guys are adding to the alternator (I like this idea and want to copy) - what is the recommended size for this strap/wire ?

Bet you never made that mistake again

All well and good, BUT, how is the connection between the aluminum shroud and the case and the case with the chassis?

So good that my car turns over faster than ever before. Almost scary fast. The original ground strap and the body to battery strap is still there.

Thick. Dunno what gage I used on mine. I just took a fat bit of wire and put some ends on it and put it on the car.

Zach

Now you got me all worried that in my attempts to get the car started I damaged the throttle cable. The cable isn't behaving badly but...

Six gauge is what I am using but this isn't on the alternator itself.

Remember, the longer the wire the fatter the gauge, for the same amount of current.

Yeah, this is pretty short, 16 inches I think. The starter cable is a 4 gauge if I remember correctly. I am going to pull the transmission ground strap next chance I get and clean the crap out of it and the connections. Leaving my additional ground in though. It was so nice hopping in the car this morning on the way to work and hearing it spin that fast. It was almost scary. I have a point higher compression than stock too. My voltage regulator/alternator is working better as well. I just checked and it's dead on 13.75 steady. Oh, and my fog lamps are working again, not sure what's up with that. If I don't have to do the LED upgrade blue/white ground hack I would be happy.

@vaccarabite
Zach; I like the fan shroud to chassis ground idea. Can we chat when you’re here on the 14th?

Don't think the fan shrouds are aluminum.

I was thinking the same, they are magnesium .. but then so is the tranny case - so I guess it doesn't matter.

The electrical connection from the fan shroud to the engine case, and the engine case to the transmission case should be excellent, much better than the chassis itself. That is how the alternator is grounded to the chassis in all 914's.

There was some talk of current through bearings and gears, but IMHO that is totally insignificant. The fan housing bridges the two engine case halves and the case bolts do the same. If you keep the battery and transmission ground straps in place, then I see no possibility of problems

I agree. The German engineers knew what they were doing. The strap width and design takes into account any anodic activity and is the reason it is designed as it is. After 50 years of salt, rain or snow, the reason it should be replaced every 50 years or so. Mag is the most reactive metal, but light and strong.

Key phrase is "Mag is the most reactive" mix that in with a bit of salt spray our Northeastern cars get and

It is interesting that on all of my other projects over the years very few ground strap issues have arisen. I have had grounding issues for particular sensors and such but nothing like a clutch or throttle turning into a ground strap. I wonder why it's such a common issue on the 914. Maybe the location exposes it to too much road crap and acidic oil blow off? Just saw the 50 years of salt post. Mine was 1 year old... Of course the case and body are not.

@emerygt350

Wow. There's a lot to unpack with your ground issue. Some questions:

When did this issue start? Did you change anything?



Is this wire from the battery NEG to engine case in addition to the normal battery NEG to chassis?

In this case, you've paralleled the new wire with the OEM current path. The OEM current path is battery NEG to chassis lug, then panel to panel to panel to the lug above the trans to the trans strap. If there's some issues panel to panel then you still have an issue with chassis ground as the entire chassis should be at ground. All electrical components use chassis as ground. If your chassis isn't a good ground, the issue is still there. The added cable helped the starter current loop but may mask the real issue.

Do you have the OEM voltmeter in the cabin? If so it would be interesting to see if it changed.



This may indicate a better ground at the gauges now. Question is what is that path? From battery NEG to engine case. Then where? Either through the accelerator cable, or the engine case to trans case to trans lug. If you were to connect your new cable from battery NEG to trans case bolt I bet it would work just as well. There might be something going on with the lug behind the battery or that panel.



@VaccaRabite

One of those discussions was for Zach's alternator issues. Turns out powder coating the fan shroud inhibited the ground return for the alternator. A ground strap from alternator case to chassis solved the issue.

Interesting! Yes, I kept the post to body ground. Just added my new one to the existing. Ground strap is still there. I ran my multi all over the place from grounds to body, to battery etc and all was fine (except the POS to starter cable, that was good but variable so I replaced it). It really was only when heavy draw was happening. As soon as I get a free moment (college just started back up, so my time is precious for a couple weeks) I will pull that ground strap and get a good look at the contacts and the strap itself.

The issue was over night. One day everything was normal (but nothing like now, I didn't know my starter could spin an engine like that) and then it would hardly turn over. I was noticing some oddness though. Backfiring through the TB when having fun kicking it at 3k (she really loves 2.5 to 5k) I would randomly get light rattle can backfires through the TB. That became a major thing after I lost my ground got it started and took it for a drive. So it seems like I was losing all ground at that point. That was the day I figured it out.