Jon M Posted April 12, 2023 Report Share Posted April 12, 2023 Before we could get our 78 J home to the hanger, She was outside for two weeks in the rain. She was covered but it really came down hard. Since then the fuel tank, fuel pressure, and oil pressure gauges dip when turning on the lights. (Especially the navs). I have cleaned all the light terminals. She has been hangered now for two months so I know everything should be dry. Tomorrow I will be testing the alternator draw with everything switched on just to see how strong it is. Has anyone experienced this symptom after exposure to moisture? Thanks for any thoughts here. Quote Link to comment Share on other sites More sharing options...
carusoam Posted April 12, 2023 Report Share Posted April 12, 2023 Kinda sounds like… a weak battery, or a charging system not keeping up… How old is the battery… Has it been charged lately… When did it have a capacity check run last? What battery is it… PP thoughts that come to mind when reading this question… No… things don’t dim normally unless they are on an automatic dimmer kind of switch… or a huge drain is occurring… If this occurs while the plane is running… what VR do you have? What volts do you see… if you have a JPI… it records V that it sees… including a dip in V if it is occurring… If it happens when it rains… the alt belt is known to slip and cause challenges like this… torque the belt properly… There is a procedure for that… What V do you see when the battery is charging… and when it is not charging? Pp thoughts only, not a mechanic… Best regards, -a- Quote Link to comment Share on other sites More sharing options...
ArtVandelay Posted April 12, 2023 Report Share Posted April 12, 2023 Do you have incandescent lights or LEDs? Do you have a way to monitor voltage?What happens with the landing light?What about pitot heat? 1 Quote Link to comment Share on other sites More sharing options...
DonMuncy Posted April 13, 2023 Report Share Posted April 13, 2023 Check the grounds carefully. 2 Quote Link to comment Share on other sites More sharing options...
carusoam Posted April 13, 2023 Report Share Posted April 13, 2023 Jon, Don brings up a good point… Ground wires often go missing in a plane’s life… You might want to be on the lookout to see where the ground straps are connected… One grounds the instrument panel to the frame… if it is loose or oxidized it will give the same affect as a power line not working properly… PP thoughts only, -a- Quote Link to comment Share on other sites More sharing options...
Jon M Posted April 13, 2023 Author Report Share Posted April 13, 2023 On 4/11/2023 at 9:20 PM, carusoam said: Kinda sounds like… a weak battery, or a charging system not keeping up… How old is the battery… Has it been charged lately… When did it have a capacity check run last? What battery is it… PP thoughts that come to mind when reading this question… No… things don’t dim normally unless they are on an automatic dimmer kind of switch… or a huge drain is occurring… If this occurs while the plane is running… what VR do you have? What volts do you see… if you have a JPI… it records V that it sees… including a dip in V if it is occurring… If it happens when it rains… the alt belt is known to slip and cause challenges like this… torque the belt properly… There is a procedure for that… What V do you see when the battery is charging… and when it is not charging? Pp thoughts only, not a mechanic… Best regards, -a- Thanks for the input here. Brand new battery. A Concord. I trickle charge after every flight. The alt. is putting out 13.5 with all switches on at idle. I believe it could be a corrosion issue since it started after she was subject to some big rain storms. I don't have LED's yet but they are arriving soon. I have to find the grounds and start checking those. Quote Link to comment Share on other sites More sharing options...
Jon M Posted April 13, 2023 Author Report Share Posted April 13, 2023 14 hours ago, carusoam said: Jon, Don brings up a good point… Ground wires often go missing in a plane’s life… You might want to be on the lookout to see where the ground straps are connected… One grounds the instrument panel to the frame… if it is loose or oxidized it will give the same affect as a power line not working properly… PP thoughts only, -a- I will seek out the ground straps and check them. Thanks! Quote Link to comment Share on other sites More sharing options...
Jon M Posted April 13, 2023 Author Report Share Posted April 13, 2023 (edited) 14 hours ago, DonMuncy said: Check the grounds carefully. Thanks Don. I will. Any thoughts on where to look for them? I assume I can find that info in the M20J maintenance manual. Edited April 13, 2023 by Jon M Quote Link to comment Share on other sites More sharing options...
MikeOH Posted April 13, 2023 Report Share Posted April 13, 2023 @Jon M I would look at the schematic for a common return point for the instruments that “dip” and the return for the nav lights. I suspect one of those grounds is poor (my guess is the nav light return such that it’s return current is forced to return via the other instrument ground) Quote Link to comment Share on other sites More sharing options...
DonMuncy Posted April 14, 2023 Report Share Posted April 14, 2023 To start with, you might temporarily run a wire from one of the ground posts on the instrument cluster to a known good ground. If the problem goes away, then go in and check every ground wire you can find. 1 Quote Link to comment Share on other sites More sharing options...
ArtVandelay Posted April 14, 2023 Report Share Posted April 14, 2023 Or just open the battery panel, clip a wire to the negative side of the battery and check resistance to the ground post if the gauge cluster, should be very low. 1 Quote Link to comment Share on other sites More sharing options...
thinwing Posted April 14, 2023 Report Share Posted April 14, 2023 this sounds like a corroided terminal due to high humidity from all the rain and sitting outside.I would also check and clean connections from battery to master solonoid ...something is causing a high resistance when applying a load 1 Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.