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Tachometer fluctuations due to bad alternator

8K views 19 replies 9 participants last post by  rhcdmd 
#1 ·
I am posting this and hopefully making it easily searchable to try and help others who may have the same problem. I was having problems starting my 69 and problems with dim lights. My battery could not be fully charged using a charger and I replaced it. At the same time, my tachometer had begun to fluctuate wildly. I figured I would deal with the tachometer later. After replacing the battery, I thought it would be a good idea to check the alternator which had an internal voltage regulator. It was not charging. It also tested bad at Autozone. I replaced the alternator and my tachometer began to function normally again. Glad I found this when I did because I was about to take the tachometer out to inspect and possibly replace it. I could also see my console gauges much better at night. The battery had less than 3,000 miles on it and the alternator probably had half of that. Hope this helps someone when trying to diagnose tachometer problems. All was even better when Autozone replaced the battery and alternator at no charge. (No pun intended):smile2:
 
#2 ·
Make sure the alternator is well grounded to the engine and its brackets, and that the engine IS the buss bar for the rest of the car to ground to. This means the battery negative cable needs to go to the engine, then out to the other areas to ground, NOT be an ancillary point of ground.

Rarely, those fluctuations can be caused by a diode inside the alternator going bad, rarely.

Internal regulators can, and do go bad, mostly from bad grounding of the alternator. Same goes for either point type, or Wells VR715 electronic type regulators for remote regulator alternators.

Good catch and fix on your charging, tach and lights problems.
 
#11 ·
Dave Ray, My negative cable is grounded to the engine, but I am not sure that I completely understand the rest of the last sentence of your first paragraph. Even at it's best, I have always had a problem with dim interior lights and gauges. They are better now, as I said in my first post, but not what they should be. Somebody driving behind me one time even said that my taillights were dim. He was a car guy and said that he thought I had a ground problem. I have tried to clean every ground wire that I could find. Do you think what you are saying could have some relevance to the dim lights?
 
#3 ·
Not to hijack anything here, but a grounding question.

Is there any problem grounding the battery to an aluminum head?

I know aluminum was used for basic home wiring for a time, in fact the service wire at my home right now as I type is aluminum and I do realize aluminum will not carry the same amperage compared to a equal size copper wire ... but it is none the less a decent conductor of current.

I ask because I have folks regularly point out that my battery is grounded to an aluminum head.

I also have a battery ground to the inner fender, plus another from the rear of that same aluminum head to the firewall.

I do not seem to have any problems on account of bad grounds from the battery.

Again, my question is regarding grounding to aluminum heads ...
 
#5 ·
Aluminum is just below Pure Gold and Steel is ranked 11th

Material IACS (International Annealed Copper Standard)

Ranking Metal % Conductivity*
1 Silver (Pure)105%
2 Copper 100%
3 Gold (Pure) 70%
4 Aluminum 61%
5 Brass 28%
6 Zinc 27%
7 Nickel 22%
8 Iron (Pure) 17%
9 Tin 15%
10 Phosphor Bronze 15%
11 Steel (Stainless included) 3-15%
12 Lead (Pure) 7%
13 Nickel Aluminum Bronze 7%
* Conductivity ratings are expressed as a relative measurement to copper. A 100% rating does not indicate no resistance.
 
#9 ·
High tension power lines are made of aluminum. If it wasn't a great conductor, they wouldn't use it and on top of that, it's relatively cheap.
 
#10 ·
Here's my input.

If I had a choice between connections I would choose a good connection to an aluminum head over a poor connection to an iron block. I would then if needed in a different situation choose a good connection to an iron block over a poor connection to an aluminum head.

Basically to me, a good solid connection is the important point.

I have not been exposed to different setups with let's say aluminum heads, but there are issues that can occur due to dissimilar metals. I'm not up to speed with all of that stuff but I have seen connections issues I cannot explain even though the connections were clean and tight from the start but then later, the connections go south. It could very well be due to dissimilar metals.

As far as aluminum being used as a conductor, it is being used in a lot of applications but the real importance to me is the ampacity of a conductor.

Jim
 
#13 ·
As blitzer says, good ground from engine to chassis and body are essential.

Now, think about this, everyone, stock battery ground on the engine is by either a STEEL bracket, usually for the alternator, OR, a STEEL double threaded bolt of some sort, such as for an intake manifold. So, one could say the engine end of the ground goes to STEEL, not aluminum, or cast iron.

Yes, bad/compromised grounds will make for lower head light outputs. Also, the wiring connectors at the bulk head connector on the dash can get corroded badly, which would make for low lighting output. Start cleaning/tightening, there's lotsa places to look into.
 
#17 · (Edited)
This is one on my car.

Just a typical ground strap from the back of the head to the firewall. My battery is grounded to the front of this same head.

DSC_1481 by Larry Madsen, on Flickr

Be certain to clear the grounding spot down to clean, bare metal. For the one pictured here I actually welded a nut on the back side of the firewall, so I have a 1/4" bolt holding it securely to the firewall ... not just a sheet metal screw.
 
#18 ·
I looked at some of your pictures and the best I could find, or see, was it looks like you have aftermarket cables on the battery. One could run a 10 gauge or 8 gauge from the negative cable end at the battery to a spot on the fender or radiator support or with the same sized cable, do another one from maybe an open bolt hole on the backside of the driver's cylinder head to a bolt stud on the power brake booster on the firewall face.

Keep in mind, if you do add a ground from the battery to the fender and/or radiator support, even though they eventually bolt to the firewall, if one has fenders that were painted heavily that are then bolted to a radiator support that might also have been heavily painted and then bolted to a firewall that was heavily painted, the electrical path may be poor between all of these parts as the paint is not a good conductor of electricity. I've chased issues with these things and like so many have said, you cannot have enough grounds and even going overkill will hurt nothing. One just has to keep in mind is that things even though bolted together tight may be solid mechanically, electrically, it might not be as solid in that respect.

Jim
 
#19 ·
A long time ago, I had a tach with a very jumpy indicator. I added some extra engine to body ground wires, and that solve my tach issue.

As many have already stated... you can never have too many grounds in your vehicle.
Don't just rely on the one large negative cable that runs from the engine to the battery.

There are many replacement negative battery cables that also have a smaller wire that extends out from the battery's negative terminal connector. This wire is usually connected somewhere to your radiator support or fender (... and as already stated by Larry, be sure all connections to ground are on bare metal).

I also have added a couple 10 gauge ground wires to the back of my head. One wire connects to the firewall. The other wire runs through a grommet hole in the firewall and is connected to the metal frame of my dash panel. I figured that there are a lot of interior components that ground to the dash, so the extra ground from the engine to the interior was just some added insurance.

Remember to periodically check all of your ground connections to confirm they are secure.
 
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