Can you find my missing 9 volts?

[rapid_ascent]

I'll chime in on voting for the switch. If you disconnect the load and check the switch voltage its not the same as checking the switch when it has 7A passing through it.

[knievel]

If I'm reading this right and you used a jumper wire from the power bus to the strobe and they worked, you're very close to finding the problem.

Leave the end connected to the strobe alone. With the other end start working your way down the line. I.e. switch input, switch output, etc. At some point your going to reach a point where your strobe do not work. At this point you just crossed the problem point.

[Kahuna]

Rosie,
Your on the right track. Voltage check across a switch with no load is not particularly useful. Report back. Im betting on the switch.

[BillL]

I think I might find something to load the circuit at the strobe, maybe an incandescent landing light? (or several) Something under the range of the circuit and fuse, then check voltage and look for the hot area, switch or somewhere along the circuit. Or, check voltage across devices.

It could be upstream of the switch too, all the way back to the buss.

Good luck, finding the solution will be rewarding and relieving at the same time .

Funny story, I was a fresh service writer/mechanic at a dealership, with no service manager on the scene (hard times), I would write tickets on a short and found one mechanic very quick at finding and repairing the issues. I wanted to know how he did it. Reluctantly, he showed me. He would take a heavy wire direct to the battery hot side and touch the wire, it got hot, quick. Then he would run his hand down the harness and find where it got cool, then he had located the area of the short. I coined this technique as "follow the smoking wire" Crude but very very effective, and with skill, no damage. Brilliant.

[tim2542]

Like Vern said...and strobes are known switch killers.
And like Kahuna said, you won't see the voltage drop unless the circuit is loaded, or the switch is totally failed. Using a little Bosch cube relay may be a good option if it dies again later or you want to prevent it from happening again.
Tim

[bjdecker]

Paul,

I had the same issue on my -7 and Whelen strobe pack at about 125 hours. Output of the switch was ~12.6V and ~3V at the pack. Voltage was measured at that point of connection to local airframe.

The switch had failed AND about 2 inches of wire had "burned" resulting in a very high resistance path.

The root cause of the failed switch and wire was faulty termination at the switch (bad crimp).

I ran a new section of wire from the switch to the Whelen, properly terminated both, and installed a new switch.

All good after 250 hours.

[vlittle]

Originally Posted by bjdecker

Paul,

I had the same issue on my -7 and Whelen strobe pack at about 125 hours. Output of the switch was ~12.6V and ~3V at the pack. Voltage was measured at that point of connection to local airframe.

The switch had failed AND about 2 inches of wire had "burned" resulting in a very high resistance path.

The root cause of the failed switch and wire was faulty termination at the switch (bad crimp).

I ran a new section of wire from the switch to the Whelen, properly terminated both, and installed a new switch.

All good after 250 hours.

The root cause was likely the switch, not the crimp. See http://www.vansairforce.com/communit...Carling+switch.

I spent a lot of time and money chasing this down. Here is what a bad switch looks like.... It takes the terminal with it. BTW,this is a strobe switch.

[rocketbob]

Taking voltage readings at various points isn't a good way to troubleshoot.

Because...V=I*R.

If I (current) is very low, the few microamps of current passing thru the voltmeter with a high resistance R, voltage at the switch will read close to the battery voltage.

The real test is to disconnect the switch altogether and measure the resistance with it on. If its more than a few milliohms, it needs to be replaced.

[Pat Falley]

I had the exact same problem, my strobe stopped working, low voltage at the strobe input. Re-crimping the wire terminal leads fixed the problem. Problem occurred at 1300 hrs.

I'm the 3rd owner, the main point is don't use automotive parts store crimp connectors, they seem to fail. I've had to replace a lot of them.

[Rosie]

Originally Posted by Kahuna

Rosie,
Your on the right track. Voltage check across a switch with no load is not particularly useful. Report back. Im betting on the switch.

I'm listening to all the SMEs (Subject Matter Experts) - thank you for all the replies; a new 10 amp switch should arrive today from Aircraft Spruce....with Spruce just over the hill, I get next day delivery for the price of first class mail! By the way, the wire runs are 1-piece (no splices) from the panel to the pack, Tefzel 16 gauge.

I will report back Rosie