my overdrive dashboard light has developed a habit of coming on while driving. It does it slowly...as in it starts out as a very faint light and slowly becomes fully illuminated.

It's a 1989 740gl.

Any ideas as to what is causing this? And can it / will it lead to trouble?

thanks

 

that OD light should toggle on/off when you put the OD lockout button. I can't think of any scenario that would make it dim except a bad OD relay or OD solenoid or wiring.

 

the OD light will go on/off when I press the button on the shifter. but when the light is off it sometimes comes slowly on

thanks

 

the OD light circuit is like this...

the OD relay has two outputs, both wired together internally, pin 87 and 87a. these outputs are either switched to +12 or to ground. the OD light is wired between pin 87a and ignition power, so it will light if the relay is grounded, and be off if the relay is +12. the OD solenoid (which is on the side of the transmission) is wired between pin 87 and ground, so it will be powered if the relay is +12 and unpowered if the relay is ground.

that's right, the light and the solenoid are opposites. light on == no power to OD solenoid. light off == power to solenoid. when the solenoid is powered, it opens a little hydraulic valve that lets fluid flow inside the transmission which in turn enables the automatic OD/4th to shift when it feels like it.

 

Start by changing the OD relay. Most problems with the OD are relay related.
Is this the ONLY light that comes on like this? No other dash lights?

 

yes...it is the only dash light that does this

 

Mine does that too. I have to slap the right side of the console near the bottom to make mine shut off.

I suspect dodgy connections in the fuse block. It's on my list...

 

These are Circuit Board problems usually. The solder points on the board need to be refloated. They manifest themselves in all kinds of ways like you guys describe. The OD light alone may be the relay but all other light/gauge anomalies can normally be traced to the board.

 

When you say circuit board, I'm assuming you're meaning on the back of the instrument cluster? Because my E-brake, Battery, and Light Warning lights do this as well.

 

He's referring to the circuit board in the OD relay. They are notorious for developing cracks in the solder joints leading to issues such as yours. Simply pop the top off the relay and re-flow all the solder joints on the little circuit board and you should be good to go.

 

No, I do mean the circuit board on the back of the instrument panel! Especially if there are other lights besides the OD or any anomalies involving warning lights, gauges, etc

 

Do you by any chance have a diagram of the back of the instrument panel?

 

the Volvo wiring diagrams don't detail the instrument panel, just the connections to it.

 

There's no telling which solder is failing. I refloat ALL points, use a low heat soldering iron, put it on the solder, wait until solder liquifies, go to the next one. I do this to all of them, hasn't failed yet. Usually happens to the '91 and later (new style) pods though, not to so much to the earlier ones. Also, make sure the screws are tight, uncorroded.

 

I still maintain that the issue is the little circuit board within the OD relay. @Lev - he stated that this is the only lamp that is affected, not other dash lights. The instrument cluster has a separate spade that has a single positive trace that runs to the OD lamp in the cluster. This trace has a single solder joint where the spade is connected. I doubt that it failed.

My past experience and Dnarby's response that he hits the console to make it work tend to point to the relay - which is located in the console.

 

Well, yeah, first I'd change the relay, and if that doesn't help I'd go onto the board--that's what I said in my first reply. It's much easier to swap the relay than mess with the board. That's why I also asked if the OD light was the only light that was acting up...

 

Ok. Read all. My light stays on all the time. Relay works. While the button and feature are not engaged, the constant light does seem to pulse a little. Any other thoughts since the switch works ? Thanks in advance.

 

what year/model car? automatic or manual ?

 

1986....automatic

 

You should unplug the wire for OD at cluster and then check it for boltage. It should have 12v or zero volts ONLY. Anything in between and you found your problem.

Its the wire to the lower corner of the cluster.

Please get out your favorite voltmeter.



EDIT- ISn't this the SECOND old thread you have bumped that isn't yours? Bad forum etiquette, dude. Also a good way to confuse people and get poor responses. Start new thread!