Glow plug light will not go off

[boeing1]

suggest find what failed, switch relay, ect. and replace to original config. just adding a switch could possible add to problems in the future.
as of using boat as is, those glow plugs draw lots of amps

[belizesailor]

Originally Posted by landonshaw

Thank you the insight into the relay. Is there a way to test it?


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A relay is a simply a switch that is activated by applying current to one or more pins. This will close the relay and should close the circuit between other pin(s). On this type of simple SPST relay you just apply power to one pin to close the relay...that is what is happening when ignition is turned to pre-heat position.

Most relays have a basic circuit diagram on the housing. You can use this to set up a test. With this type of relay you just need power to one pin to close the relay and a multimeter to test continuity/resistance (high resistance indicates a problem too). You can typically hear the relay close when power is applied.

Another problem on the MD series is that shorts etc can damage the bases the relays connect to. Also a short in the wire harness leading to these bases can melt insulation and create other shorts.

These are standard automotive style relays. Dont pay stupid $$$ to Volvo for one. You can pick a replacement up at any auto parts store.

For example, Bosch makes relays that will work. $8.99 on Ebay now. I carry several spares. Often it is easier just to swap suspect relays becuase testing with a multimeter can sometimes be less than conclusive and relays tend to behave inconsistently more often than just totally failing, so faults can be hard to confirm.

All that said, these are "nornally open" (NO) relays and usually fail open. So, I would bet on an ignition tumbler issue as most likely.

[a64pilot]

Until you figure it out though, you can as you say disconnect the wire but protect it is it is a high amp connection, you don't want it shorting to anything.
Often glow plugs aren't really needed unless weather is really cold


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[landonshaw]

Turns out it was the switch. I turn it bit more off and the glow plug light turns off, instruments stay on. Easy fix. Now, can the spring be replaced, or do you have to replace the key mechanism? To expensive to replace.


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[Reefmagnet]

Try some dry graphite lock lubricant

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[landonshaw]

Can you take the unit apart or do you put it in where the key is inserted?


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[Reefmagnet]

Squirt it in the keyhole and then work the lock a bit.

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[Jim Cate]

How nice (and how unusual) when the cheapest and easiest cure is the correct one!

Lucky you!

Jim

[landonshaw]

Yes, thanks to all for your comments. I will also look at the relay and that suggestion for any future issue with relays.


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[GordMay]

Originally Posted by Reefmagnet

Try some dry graphite lock lubricant

Rather than penetrating oil or graphite (which might short out the electrical contacts inside the switch); use a nonconductive lubricant such as dielectric silicon grease or aerosol electronics cleaner.

[Reefmagnet]

Originally Posted by GordMay

Rather than penetrating oil or graphite (which might short out the electrical contacts inside the switch); use a nonconductive lubricant such as dielectric silicon grease or aerosol electronics cleaner.

Good point. I think the contacts inside a generic one piece ignition barrel tend to be reasonably sealed, but you'd probably not want to lather a conductive powder in there!

Come to think of it, if the switch is exposed to the weather, regular sprays with silicon spray might be the best solution. That's what I used to do every couple of weeks with my exposed to the weather switch on the previous boat and it worked flawlessly.

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[belizesailor]

Originally Posted by landonshaw

Turns out it was the switch. I turn it bit more off and the glow plug light turns off, instruments stay on. Easy fix. Now, can the spring be replaced, or do you have to replace the key mechanism? To expensive to replace.


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Not designed to be serviceable.

Cleaning and lubing is not a bad maintenance idea, but it wont fix this particular problem.

This is why Im still bumping my back just a touch many years after encountering this problem.

Probably caused by a ferrous metal spring in these "marine" parts. Which for the price should have all non corrosive parts AND be serviceable.

[boeing1]

I would replace, not expensive, check defender or other on line marine parts, about 20.00,

[landonshaw]

I would replace? Not sure what you are commenting on. Is it the key, or a relay. Thanks for your help.


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[belizesailor]

Originally Posted by boeing1

I would replace, not expensive, check defender or other on line marine parts, about 20.00,

Where did you find a replacement for $20?

I agree it SHOULD be about $20, but almost nothing from Volvo is $20....try over $200. From Marine Parts Express below, and their prices are a little better than most Volvo distributors.


PART NUMBER PART DESCRIPTION BRAND RETAIL PRICE YOUR PRICE

3587072 STARTER SWITCH Volvo Penta $218.41 $209.67