My original thought when I acquired my new F-15 throttle handle was to simply test all the individual pins & create a wire map of all the switch circuits. Well, with a 37-pin cannon plug, that was a little easier in thought than in practice. After hunting & pecking for a while, I decided that it was time to dissect the throttle handle and see what exactly I was dealing with . . . and I’m glad I did.
I had already made up a pin-out diagram for the cannon plug & numbered each pin. Since I wasn’t able to figure out the circuits for the switches or visually see them, I clearly wouldn’t know their functioning until I cracked this thing open.
The first thing I saw when I opened the throttle handle up was the flat joystick-style switch that sits on the outboard, front side of the throttle handle. It took me a while to carefully dig out the potting material & get the wires situated to the point that I could finagle this thing out of there. It was a very tight fit!
I then began digging out the other top switch from its potting goop. I identified the wires & listed them by color on another sheet of paper. I set about confirming their connections by performing a continuity check by placing one side of my test lead on a switch terminal, then at the cannon plug side I would simply swirl the test lead around until the voltmeter rang out. Then I would annotate it on my diagram.
After I finished the top switch & had all its info documented, I would then spend another 20 minutes or so excavating the next switch from its potting material prison. Once its leads were exposed, I again performed a continuity check to figure out the cannon plug pins.
After determining the wiring schema for all the switches on the throttle handle, I discovered some key pieces of information:
a. I am going to completely rewire the switches in this throttle handle. Clearly these switches are configured for specific discreet electrical components on the F-15, as evident by the myriad of capacitors, resistors, etc. hanging all over each switch. Plus, there is far more extra capacity with a 37-pin cannon plug than I am going to need to drive my components with the switches on hand. My initial thought is that even a 23-pin plug will give me plenty of future scalability.
b. I’ll be removing the pistol-shaped switch that engulfs the entire interior left side of the throttle handle. It may provide more capability when linked to specific F-15 systems, but in my case it only offers me a single-position momentary on. It takes up a lot of real estate and it’s heavy, accounting for almost 20% of the current weight of this handle. If I get rid of this switch by replacing it with a nearly externally identical Otto switch (with much smaller internal guts), reduce my throttle handle wiring harness by nearly half the wires, and use a smaller plastic AMP connector, I think I could reduce the weight of this handle by about half (about 0.65 lbs).
For those of you that are curious about the current throttle handle switch functions, they are listed below this pic in order starting at the top right-hand switch (flat grey) moving CCW.
1. Grey flat joystick style: single momentary on (TBD).
2. Black push button: PTT – single momentary on.
3. Black push button: single momentary on (GTN650 remote or Trio AP fuel data)
4. Metal china-hat toggle: ON-OFF-ON (possibly air brake)
5. Black push button: DPDT dual momentary on (TBD).
6. Grey-capped toggle: 3-position (broken lead/functioning TBD… ON-OFF-ON?)
Also, as I mentioned in my last post, for those of you that are curious about the size & fit of the F-16 throttle handle, I shot a couple pics to show what I was talking about.
Not terrible at all, but definitely takes up more space than I’d like it to inside the Long-EZ cockpit.