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kritsher

Well Known Member
After completing the firewall forward wiring harness section (Section 45A) I applied power for the first time and absolutely nothing happened! (On the bright side, I don't think any of the magic smoke escaped.)

When I turn on the master switch, there is no LED indication on the switch and the cooling fans do not move.

There is about 13V at the battery side of the master relay and basically zero volts on the other two terminals. These values don't change when I flip the master switch off/on. I hear no clicking in the master relay. The red band on the diode is oriented correctly. I have a good ground from the battery to the airframe.

Do I have a bad master relay? A bad master switch? Is it safe to put a jumper across the master relay for trouble shooting purposes? Do I need to connect power to any wire besides P150 (which connects the battery positive terminal to the master relay)?

Any suggestions welcome.
 
Sounds like it...

No click and no voltage on the output side means bad solenoid to me!
A jumper is the same as the solenoid working so that is what I'd do. Pull the fuses on all but a few things if you want to be cautious.
 
Does the small terminal from your master relay go through the switch to ground? Try just a positive from the battery to the master relay. Ground cable connected, diode disconnected. Ground the small terminal and it should click closed. If not, your relay is bad or it has resistance to ground (bad mount).
 
Assuming the fat wire from the battery is connected to the correct terminal on the contactor, then the master contactor coil is defective, based on your description. With the master switch turned off, there should be 12 volts measured between ground and the small terminal of the contactor. Since there is not 12 volts on the small terminal, that tells me that the coil is open. There should be 12 volts on the small terminal whether the contactor case is grounded or not. No additional tests are required. Zero volts on the small terminal (with master switch off) means the master contactor coil is bad. Replace the contactor.
Do I have a bad master relay?
Click to expand...
Yes!
A bad master switch?
Click to expand...
No, it is unlikely that there are two problems.
Is it safe to put a jumper across the master relay for trouble shooting purposes?
Click to expand...
No.
Do I need to connect power to any wire besides P150 (which connects the battery positive terminal to the master relay)?
Click to expand...
No.
Joe Gores
 
Check again. Have you wired up the relay correctly. I had a similar problem with a starter relay and had not wired it correctly. I was using the wrong terminal.
 
The only possible wiring error that could result in zero volts (with master switch off) on the contactor small terminal is if the positive fat battery cable, WH-P150, is connected to the wrong terminal on the contactor. The contactor would have to be mounted upside down to get it backwards if wired according to plans page 45-07.
Kritsher said he measured 12 volts on the contactor large terminal. That means that his voltmeter negative lead was well grounded. As he turned the master switch on and off, the voltage on the contactor small terminal should alternate between 12 volts and 0 volts. But it never went to 12 volts. It stayed at zero volts.
I measured the voltage between ground and the small contactor terminal on my airplane with the master switch off and got 12.93 volts. Why doesn't Kritsher's small contactor terminal measure battery voltage? Because the voltage is not getting through the contactor. Either the contactor is mounted upside down or else the contactor coil is open.
Joe Gores
 
upside down!

Joe and Yen nailed it. Thanks guys. I was careless and had mounted the relay upside down, and thus wired it up wrong. Thanks for all the helpful insights.

Meanwhile, while the relay now works, I'm uncovering other issues...

My Skyview powers up, and I can get power to the Garmin radio, but the two cooling fans do not turn (no voltage at the spade connector) and the trim motor is non-responsive (I know that it moves when power is applied directly to the pins in the 25?-pin connector because I had to test that to determine direction-of-travel before inserting those pins).

Sounds like power is not getting somewhere it needs to be. The fuses are fine. I double-checked all the harness connections. I haven't yet dug into the details of the schematics. I'm hoping that someone here might have some more useful advice.

EDIT: I should have checked the forums more carefully first. I'm guessing the fans aren't moving because I pulled the fuel pump fuse. My leading theory for the trim is that the potentiometer is not adjusted correctly, so I will check that tomorrow. If anyone has any other theories I should check, please send them my way!

Thanks!
 
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kritsher said:
EDIT: I should have checked the forums more carefully first. I'm guessing the fans aren't moving because I pulled the fuel pump fuse. My leading theory for the trim is that the potentiometer is not adjusted correctly, so I will check that tomorrow. If anyone has any other theories I should check, please send them my way!

Thanks!
Click to expand...

The fuse is the cause of the fans not running. If you want to test them, you can operate the pump for a couple seconds without any danger of damage. Just don't leave it on for an extended period with no fuel.

The trim speed is bench tested and adjusted, but it is possible that it is incorrect (though all you would likely see is it move very slowly).
The standard starting point adjustment is about 7 turns counter clockwise from fully clock wise. It is a 25 turn pot., so turn it a bunch of turns CW and then 7 turns CCW. I still wouldn't do this until after checking that the pins in the d-sub aren't pushed back inside, and that you can actually run the trim motor by connecting a 9 V battery between the 2 pins.
 
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