Because Owning And Flying Your Beechcraft Can Be Done Safely AND For Less Money!
  Alternator Out Light Install (Early Baron & Maybe Bo)


Alternator Out Lights: If you don't have an alternator out light OR a voltmeter, I don't think you'll have a good handle on your electrical system, but that's just my humble opinion. Those old ammeters can be pretty squirrelly to see a discharge and they're usually not easy to see at the moment an alternator failure occurs. The B55 I have and many other B55 owners report that the alternators hardly ever parallel and share load so that you can see some load being taken by both alternators indicated on the ammeters.


Lots of Baron owners end up looking at one ammeter showing a load and the other at zero. One would never know if the alternator showing zero load had failed, until it was too late! This issue has troubled me for several years and I finally solved it with alternator out lights that were optionally configured in later Baron models. Here are ways that this can be accomplished, with your A&P's blessing of course.


Below is a picture of my Alternator Out Lights using aviation PTT lights, MS25041.



My green lights have since been changed to blue lenses that I was able to source at ASOD.



Most older Barons and maybe Bonanzas with belt driven alternators use the Delco or Prestolite design. First, take a look at the Alternator Wiring Diagram PDF extract HERE to see the various factory alternator out configurations. You will see references to Alternator Out lights and annunciators using a relay and also a "sensor". I think the sensor is just a microelectronic relay, but don't take my word for it.


With this info you can see exactly how the factory used the "AUX" terminal of the Prestolite alternator or the "R" blade connector on the Delco alternator. These terminals provide one-half the voltage rating of the alternator when the alternator is making juice. So, on a 24V system, this will be in the 12.5V - 14.5V range. This is key, because it will allow you to use a conventional CSOB 12V DC relay available at Mouser, OnlineComponents, Allied Ellectronics or NAPA with or without a socket base, to configure your alternator out light.







Here is how one might wire a conventional 12V DC Relay for Alternator Out light functionality with a MS25041 PTT Fixture:




These are the Delco Alternator PNs from the B55 TCDS: 50 Amp Delco-Remy 1100685, 1100718 and 1100747.



Here is an excellent AC Delco connector found by Bonanza TC owner Brandon E. for his Delco alternator,  PN: PT2069 for consideration that can be found on eBay or Amazon which will make your Delco Alternator Field and "R" connections much more robust.




Here is what the PT2069 connector looks like in the Delco case, a very nicely insulated connector for those two terminals, in my humble opinion




Here is an approach taken by a Beech Lister for his alternator Out light install:


He used the Lamar relay PN: A-00258-2, $77 ea from since it is called out on the B55 wiring diagram/parts catalog. This relay is also used by Piper under PN: 587 857. He also used the Sloan lights as they are reportedly the supplied lights for current Beech models            PN: 102-SI lights & 102-STD-RTP red lens, a few bucks from


See the Sloan Light Bulb Data Sheet HERE or use conventional PTT MS25041 (Push To Test) aviation fixtures.


Another approach to the project  for review with your A&P with Delco alternators might be:


Go to National Aviation Parts of America (NAPA <grin>) and buy a single female plastic covered blade connector with a little length of wire attached, see pic HERE (or, better yet, get the PT2069 connector above). This will go on the "R" terminal of the Delco regulator, see pic HERE, (use a regular ring terminal if you are connecting to the Prestolite AUX terminal) and is nice because the plastic housing around the female connector insulates the connection from alternator case grounding (a bad thing) and the "F" field terminal which is right next to the "R" terminal. Use of PT2069 connector will give good insulation between the terminals and the case body.


Find a glass fuse holder and insert a 2 amp glass fuse in it. Connect this fuse very close to the "R" terminal connector that is connected to the "R" terminal of the alternator.


Now get the best 12V relay you can find (see above suggested components) and a connector base that plugs into the relay with short lengths of wire for relay connections or use the Lamar Relay PN: A-00258-2 or the same thing under a Piper PN: 587 857.


Connect the fused end of the "R" terminal bladed connector you put on the alternator to one side of the relay actuating coil. Ground the other side of the relay coil to the grounding lug on the alternator.


Connect ONE side of the NORMALLY CLOSED contacts of the relay to the alternator ground lug.

The OTHER SIDE of the NORMALLY CLOSED contacts of the relay will be carried up through the wing to the #2 Terminal of your PTT  (Push To Test) bulb or whatever annunciator light you are using. This is carrying GROUND up to your PTT bulb through the wing so no dangerous voltages can short out in the long wire run in the wing.


The PTT bulb is wired to +24volts from the master bus on the #1 center terminal. The #3 terminal of the PTT bulb goes to ground (so you can test it). The #2 terminal of the PTT bulb, goes to the wire you just pulled through the wing. You'll need two 24V lights of some sort. Red, blue or amber lenses work well and you can find them at the salvage places listed HERE.


Use some very nice placard from  "L Alt Out" and "R Alt Out" and you have a professional install that any A&P would be proud to sign off.


Here is what happens in the wiring circuit:


Alternator not running or running and NOT making juice = no 12-14V juice at "R" terminal. So: Normally closed contacts carry ground up to PTT bulb and bulb lights up. Things are BAD!

Alternator running making power = 12-14V juice at "R" terminal. So: Normally closed contacts OPEN UP and remove the GROUND from your bulb. All is good!


A location suggestion for mounting the relays in a Baron is the backside of the cowl door baffle (through one of the rivets with a nyloc nut and screw) that is right next to the airbox. This makes all your wires very short and a compact and tidy install. You can loosely wire tie the fuse and wire bundle to the scat tubing going to the alternator without crushing the scat tubing.


Hi resolution panel picture of my Alternator Out Lights installed (green lenses have since been changed to blue, when I find red ones I'll use those) HERE.



A great article in the October 2008 ABS Magazine, written by John Collins on page 10998 and 10999, discusses the history of the alternator out lights and the components and how they work in the system.


Some very interesting Beechcraft parts, available at RAPID,  outlined in this article that could be of interest to you and your mechanic in retrofitting your system with alternator out lights are:


P/N 36-380000-1 (14V Alternator Out Sensor) $196


P/N 36-380000-3 (28V Alternator Out Sensor) $122



P/N 36-380000-11 (Baron Replacement Alternator Out) $119


P/N 55-3025-1 S (Replacement PCB Kit) $108



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