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Hard start relay issue
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Jbvw412
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Joined: August 07, 2021
Posts: 5
Location: United Kingdom
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PostPosted: Mon Oct 24, 2022 1:01 am    Post subject: Hard start relay issue Reply with quote

Morning all,

I have a 1973 412 and since I bought it I could never get it running.
When I went to view it the owner did some trickory to get it running but I could never get it going.

Anyway, after some investigating I found the previous owner had a loose cable that connected to the bottom terminal on the starter and loose in the cab.
To start you had to hold the cable on the positive terminal on the battery and then turn key. So jumping the starter.

I put the cable right and all the starter does it click once.

I bought a new starter.
Still one click.

I fitted a hard start relay.
New cable from ignition switch to relay.
New power cable from battery to started.
New power cable from battery to relay.
Decent ground on relay.
Still one click.

However if I hold the key open for around 10 seconds the started may start to turn over. May not.

Any ideas??
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Jeremiah Berger
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PostPosted: Mon Oct 24, 2022 3:54 am    Post subject: Re: Hard start relay issue Reply with quote

Hey I responded to your post on Facebook as well...really sounds like the ignition switch to me.

Jeremiah
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raygreenwood
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Location: Oklahoma City
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PostPosted: Mon Oct 24, 2022 8:35 am    Post subject: Re: Hard start relay issue Reply with quote

It's possible that it is the ignition switch as noted......but just as probable that it's a ground issue or a corrosion issue.

Understand....that unlike the type 3 cars where the battery was under the back seat and not more than 3 feet from the starter, type 4 cars are roughly 5-6 feet further away with a lot of weld joints and rust joints between the battery ground braid stud on the pan and the ground strap braid on the tail cone of the transmission.

I must state this for effect:

Three connections on 411 and 412 that I have found to give the MOST starting amperage issues and the most voltage drop issues for the fuel injection, ignition and heater system.....are

1. The ground braid and stud at the battery and the pan underneath it. This is especially so if you see ANY green dusty corrosion on the ground braid....even if the connections at each end are clean. I will explain that one in a moment.

2. There is a 10 gauge positive wire with a shielded end that connects to the + side of the battery. If this is loose, has corrosion etc....will can and will give one of two results.
A. If it's disconnected or loose enough to have 0 connection....when you turn the key, fuel pump will buzz, everything looks and works normal....but no starter action whatsoever. Not even a click.

B. If its just poor connection....same as above but not enough power to drive the starter. Just a click from relays and solenoid on starter.

3. The ground strap on the tail cone of the transmission. This is the big killer for much the same reason as the ground braid at the battery. This is the single worst offender as its in a high vibration area and down in the weather. It has multiple issues.

A. If you see green dusty corrosion on the outside surfaces of the ground strap....even if the connections to the chassis and transmission are clean.....the current carrying capacity is WAY DOWN. I will explain further in a moment.

B. There can be issues at the stud on the chassis where it originates. You need to take the strap loose and clean until all parts shine and re-tighten.

C. The point where it bolts to the tail cone of the transmission is a very small contact area and prone to getting oily....which is a dielectric and does not conduct well...and it gets loose easily.
So if you also have green dusty corrosion on the ground strap which means ability to carry current is low.....the very small contact area with the tail cone under the nut....with any oil or looseness at all....can totally prevent starter action.

Ok.....the green copper ground strap thing.

Among conductive metals.....metals that "tarnish"......with copper, as it gets that normal dark "old penny" colored look....that oxide is roughly 25% to 40% LESS conductive than bright copper.
When it finally gets any white or green color on the surface....that oxide is nearly 100% non-conductive.
This is why for example in electronic circuit work and especially with Aerospace and medical devices...we are not ALLOWED to use bare copper.

We have to use silver for common circuits.....because the dark Grey to black patina of oxidized silver....is still nearly 90% conductive. In super critical areas we have to use gold. In non body contact areas we can use tin or nickel.

A ground braid is a great carrier of high current compared to even a 1 or 0 gauge battery cable....because it has a lot more total cross section of copper when you calculate it out....and it has the benefit of being a lot more flexible. That's why they use braided straps.

But.....electricity....electrons.....have a tendency to flow through the areas of least resistance. This means a lot of the current carrying capacity of a ground braid is along the outer surfaces of the wires in the braid. So once you get green or white corrosion all around and through the outside of the braids....all of those outer surfaces become non-conductive. The capacity of that braid drops very low.

You will find these braids getting hot while trying to start....which drops carrying capacity even further.

A battery cable of 0 or 1....keeps its cross sectional carrying capacity longer...ad long ax its still tightly packed together inside of its sheathing and the sheathing has protected the surfaces of the strands from oxidizing.

But....one of the big killers of the large gauge, sheathed stranded copper battery cables....is that exposed short section where the cable exits the sheathing and it clamped or can't into the battery connector. If green corrosion blooms between the strands at this point.....it can cut the carrying capacity in half.

Out of all wire types....a solid core large gauge wire would have 0 issues because 98% of its cross section is inside and is not subject to corrosion or moisture. But it's also not flexible at all.

You also find ground braids that have been tin plated. These last longer in one respect in corrosion prone areas.....but have a worse problem. They should be avoided.

The problem is that if ground strap is very close to a positive power source...over time....the tin will literally....electrolytically..... "grow" small feelers of tin called "tin whiskers" across the gap...shorting things out.

Its a great idea to buy new ground straps on old cars. Dip and wash them in a light acid to make them bright. Vinegar will work. Then soak them in baking soda and water to neutralize. Give them a rinse/soak in distilled water. Take them out and heat in a toaster ivern or with heat gun to about 250°F to completely dry them out.

Then...all except for the ends where they connect....coat them completely with either a good RTV or I can recommend a flexible dielectric coating like those used on circuit boards you can get at on line shops.

This keeps oxygen and moisture out of the braids for a long time.

Ray
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KTPhil Premium Member
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PostPosted: Mon Oct 24, 2022 8:45 am    Post subject: Re: Hard start relay issue Reply with quote

Any chance the "start in N or P" switch at the shifter is faulty?
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raygreenwood
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Location: Oklahoma City
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PostPosted: Mon Oct 24, 2022 10:41 am    Post subject: Re: Hard start relay issue Reply with quote

KTPhil wrote:
Any chance the "start in N or P" switch at the shifter is faulty?


I thought about that one too....but if that switch were not making contact....he would not get a click from the starter.

Ray
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scottyrocks
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Joined: August 19, 2016
Posts: 2645
Location: Long Island, NY
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PostPosted: Mon Oct 24, 2022 12:15 pm    Post subject: Re: Hard start relay issue Reply with quote

Thank you, Ray, for that information. Stuff like that is golden.
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