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Author Topic:   Corrosion on Relay contacts
dgoodhue posted 05-23-2010 07:15 PM ET (US)   Profile for dgoodhue   Send Email to dgoodhue  
I went to launch my boat this morning and when I got to the ramp my power trim and tilt did not work. I was puzzled because it had worked 20 minutes earlier in my driveway as I did a quick check of the engine. Anyways, I was able to get it working at the ramp. It started working once I removed and put back in the two relays that connect to the Power trim and tilt switch. The contacts didn't look overly corroded, but I suspected corrosion is the [cause of the malfunction in the trim relay control circuit].

What should I do to prevent this problem in the future?

jimh posted 05-23-2010 08:12 PM ET (US)     Profile for jimh  Send Email to jimh     
In 12-volt circuits a very thin layer of insulation can block the flow of current. It is possible for just a very small amount of oxidation on connector contacts to affect current flow.

When a contact has been affected by oxidation or corrosion and stops conducting current, often all that is needed to restore normal operation is to remove and insert the contact several times. The process of removing and inserting the contact will scrape off the insulation layer and restore the connection. An electrical contact cleaning solution is often applied. The choice of electrical contact cleaning solution must be made with an eye to the other materials in the connector. Some electrical cleaning solvents are harmful to plastics and rubber, common materials in connectors. WD-40 is a reasonably effective electrical contact cleaning solution and is also fairly benign to most other materials found in electrical connectors. Application of a small amount of WD-40 can help restore contacts which have developed an insulating layer of oxidation or corrosion.

In a marine environment water is omnipresent, and water causes oxidation and corrosion of metals used in contacts like copper. To prevent oxidation, it is helpful to keep water and water vapor away from the metal contacts. One way to prevent water from reaching electrical contacts is to use a non-conductive grease as a means of sealing the contact area from any ingress of water. In low-voltage circuits like 12-volt distribution, almost any grease will be sufficiently non-conductive. You can use a grease like petroleum jelly or waterproof outboard grease (as long as it does not contain metals), or you can buy much more expensive and much better insulating (in terms of voltage breakdown) specialized greases, usually sold under the generic name of dielectric grease. As the name "dielectric" implies, these greases are very non-conducting. As non-conductors you do not put them on the electrical contacts themselves, but you apply them to the connectors in a way to prevent water from entering the connector and contact area.

dgoodhue posted 11-01-2010 07:14 AM ET (US)     Profile for dgoodhue  Send Email to dgoodhue     
The relays gave me problems most of the summer, occasionally not working. I pulled the power trim/tilt harness and socket out this weekend and it turns out the ground weren't even connected. I think its a miracle it even worked. It must have touching the the engine block. When the relay wouldn't work, I push on the relay which are on a 'float connector' to make them work, so that must have been making a better contact with the engine block. Cheap fix, I wish I pushed it apart earlier.

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