The International Cessna^® 170 Association

Hi everyone. I recently bought a 1949 170A (N9714A) and am still getting used to it. When I turn the Master switch on, a red light in the middle of the panel lights up. But when I turn the alternator on, the light goes out. This happens both with the engine running and not running. Is this normal? Also, I have a red anti-collision light on top of the fueslage behind the cabin. It does not have a mechanical rotating mechanism, but blinks on and off, about once every two seconds. My ammeter seems to be operating properly, showing charging when it should be chanrging and discharging when it should be discharging (like with the engine off and an electrical load imposed). That red light must have a large current draw since the ammenter needle jumps about 1/4 scale toward discharging, in synch with operation of that red light. My question, once again is...is that normal. Just trying to get compfotable with the aircraft. Thanks.

Well first it is not normal for a 170 to have a red light or an alternator. So yours has been modified to include a red light and an alternator and no telling how that was done. So it would be hard to understand the red light exactly. Under many installations there is a red light that indicates low voltage. In many cases no voltage. This is what your red light seems to be indicating because it is on when the alternator is switched off or not turning but goes out when the alternator is turning and turned on. Why the red light goes out when the alternator is not turning but switched on is a mystery to me and we are not likely to solve without a schematic how this is all wired.

The red blinking strobe is likely working correctly. However you haven't given enough detailed information and here is why. You didn't say what was full scale on your amp meter. You have said you have an alternator and so likely you might have a 60 amp range gauge rather than the standard 30 amps. 1/4, your description of the movement on 30 amp gauge is 7.5 amps. and that is not surprising. However 1/4 of 60 amps is 15 amps and that would be surprising.

Bruce-thanks for your rapid response. The ammenter goes from -30 to +30. 1/4 scale was an approximation. It bounces a bit when it makes the step change. It could be a little less than that, but it got my attention. As for the red light, for some reason I thought it was standard and it would be an easy question. That will take some more investigation.

I suggest that your alternator field has been wired with a SPDT switch that energizes the red light when the alternator is OFF to remind you to turn it ON when you're going flying, but the field will not be energised when the battery is on the buss for other work.

blueldr wrote:I suggest that your alternator field has been wired with a SPDT switch that energizes the red light when the alternator is OFF to remind you to turn it ON when you're going flying, but the field will not be energised when the battery is on the buss for other work.

YEP;... that's what I was thinkin' too. It's a "turn the alternator on stoopid warning light". (All warning-lights are stoopid....IMO.)