In my experience that's exactly what happens.

Driving a VW Cabriolet in rainy Seattle trained me to put dielectric grease on every connector I had any reason to take apart. (The inside of a convertible is almost never totally dry, and condensation gets into everything.)

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1981 Mercedes 300TD, 1994 Honda Civic Del Sol
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This direct from Wiki:

"Dielectric grease is a nonconductive grease. As such, it does not enhance the flow of electrical current. Thus electrical conductors should not be coated with dielectric grease prior to being mated. Dielectric grease is, however, often applied to electrical connectors, particularly those containing rubber gaskets, as a means of lubricating and sealing rubber portions of the connector.

The widest use of dielectric grease is in high-voltage connections associated with spark plugs. The grease is applied to the rubber boot of the plug wire. This helps the rubber boot slide onto the ceramic insulator of the plug. The grease also acts to seal the rubber boot, while at the same time preventing the rubber from becoming stuck to the ceramic. Generally spark plugs are located in areas of high temperature, and the grease is formulated to withstand the temperature range expected.

Another common use of dielectric grease is on the rubber mating surfaces or gaskets of multi-pin electrical connectors used in automotive and marine engines. The grease again acts as a lubricant and a sealant on the nonconductive mating surfaces of the connector. It is not recommended to be applied to the actual electrical conductive contacts of the connector because it could interfere with the electrical signals passing through the connector."

It's an insulator as any grease should be. I darned sure wouldn't use it on the metal contacts!

Manufacturers do......ever see the white grease IN tail light sockets.

Its actually used pretty reqular on metal contacts that are exposed to severe conditions.....like on cars.

Don't trust Wikipedia completely.....its been wrong on many occaisons.

I wouldn't use just any grease however....I have a can thats very definately conductive to electric.

Its a graphite impregnated grease used on Air Force Helicopters I bought at a DRMO sale because it hit its experation date for use on aircraft.

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

In California or any other reasonable climate oxidation of electrical connections is far less severe. The grease or whatever is just squeezed aside by mechanical pressure. So the connection still becomes valid.

The function then of the grease is just to surround the contacting surfaces basically to deny oxygen reaching the mechanical connection to start the oxidation all over again. Or semi arrest continuance of the oxides growth if already there.

Some more modern cars have started using this at the manufacturing level a long time ago in certain connections they expect to become troublesome. If the mechanical connection is not strong enough to displace the grease in the contact area the mechanical contact between conductors itself is too weak in my opinion.

It is likely to become more problematic without grease as well in that state. The oxidation will have less difficulty forming on poorly contacting surfaces. Then there is the electro chemistry between disimular metals that occurs as well.

We actually help the process if the connection is electrically weak. We land up heating the area to above ambient levels eventually as oxidation grows. It has become a resistance point to the flow of current. Or a restriction if you wish.

Since by and large costs are an important integral component of auto manufacturing. It is unwise to expect too much of a safety margin in electrical wiring systems on cars. It costs money. Also a wiring systems connections designed for your area might be overkill. Where in mine with the climatic differences and road salt introducted into the equation far more marginal. I suspect a car manufacture engineers for a ten year time frame in my locallity. The car body is likely to be toast by then if not also protected well somehow.

Basically correct in my opinion. They could add a conductive component with finely grown metals to any grease The issue then would be shorts from the paste. The enhanced reduction of the metal surfaces to oxygen access is also important.

From my 'shade tree' mechanic days, I remember cleaning a lot of battery terminals to get good contact, tightening the connectors on each post, and then smearing a good slab of Vaseline petroleum jelly over each, to keep moisture and acid fumes away from the connection. I suppose any ol' grease, dabbed on with fingers, or sprayed on from a can, would do the same job to put a moisture/acid barrier between the connection and the outside world. So, I suppose 'dielectric grease' is doing pretty much the same job here, except you trust that there will be metal-to-metal contact when you mate the connectors...

Well I used the stuff A LOT. Such as on the window switches where the bearing meets the metal tab. Made the switches a little smoother and quieter. I also use it pretty much at every electrical connection. So far no issues that I know of.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

Great post, I agree with everything said.

Ford instructs techs to use dielectric grease on many electrical repairs and there are a small handful connectors that roll off the assembly line with dielectric grease right on the terminals, notably the trailer harness connectors on the rear bumper.

Dielectric grease applied directly on electrical terminals will pretty much prevent terminal fretting, a type of corrosion that can build up on contact surfaces even in a perfectly sealed connector.

Dielectric grease can also take care of localized hot spots on electrical mating surfaces that are caused by uneven contact areas. Good for high current ground connections and battery terminals.

I do, routinely. I've never had a problem. If the contacts are tight enough to make a reliable connection they're tight enough to displace the grease, in my experience. I'll often smear up the whole base of a tail light bulb before I install it, for example. Of course, if the contacts are dirty you should clean them first.

You actually don't want the grease to be conductive, in most cases -- too easy to short between pins on a multi-pin connector that way. There are some situations that call for conductive grease, though; usually sliding contacts like slip rings and the like.

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1981 Mercedes 300TD, 1994 Honda Civic Del Sol
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Drove 140 miles this AM. Tach worked fine. I even hit a patch of dense fog that caused really quick heavy condensation to form on the windshield. It formed in a couple of minutes and required wipers to clear it.

This afternoon it worked fine as well. During both trips I played with the AC (usually kills it or turns it on ) Goofed with switches, turned lights off/on. DARING IT to fail.

1.6 miles from home. "Flomp" the needle was tired...

Made a left turn and it woke up. Did fine the whole way home.


Right before it stopped I was fooling around goosing the throttle and winding the engine higher than I usually do. About 4500 RPM.


Soooo close...

Clean the pins again and re apply grease? I didn't clean them again and just dabbed a tiny bit of grease on with a Q-Tip...

Coincidence ??

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my occupation's just not around...
1980 300SD
1980 300SD

That's why it works so well: Areas of the contact that are actually touching push the grease out of the way. Areas that would make poor contact and arc are insulated so they don't arc.

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

The tach amps themselves are problamatic. Either resolder it's circuit board or get another one. It usually is not an actual contact socket problem with them.

Your physical moving it around has probably helped reduce the intermittent condition a little. Anyways it is far from conclusive it is the connections to the car from the tach amp. Whoever built the cruise control amplifiers for these cars possibly built the tach signal amplifiers on a bad days as well.

It will not hurt to clean the pins etc again as the pulse from the sensor is weak and probably as a light resistance to flow is important. There are referances in the archives that suggest additional pressure to the unit. This seems to fix some and many have done it. Well really not fix it but skirt the problem is a better description.

Still working...

I've probably driven about 900 miles with only two short lasted hiccups. Both times the needle popped back up within a few seconds.

I'm not touching it until (IF ) it quits but thanks for the ideas!

__________________
My occupational hazard bein'
my occupation's just not around...
1980 300SD
1980 300SD