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PanJH · 03-27-2017, 05:14 AM

After I pulled into my storage lot, I pulled the 12v power plug for my TST TPMS.

The plug came apart, the fuse and spring went flying and the nose piece was still laying in the power port. I fished out the nose piece and put the fuse and spring back in and plugged it in to test. The indicator light on the power cord lite up, but the TPMS didn't work.
I get out the multi=meter and find there is 7.8v at the output of the power cord to the TPMS. I check the dash power port, same thing there. Next I go to the coach fuse and find the fuse for the power port. It's burnt. I check it with the meter and its definitely open. Now, with the fuse out, I check the power port and is still has 7.8v ! I put in a new fuse and test the power port and it is now correctly at 12.6v and the TPMS now works fine. I figure when the plug came apart, the nose piece that stayed in the power port shorted out the fuse.
Somethng is backfeeding that circuit for the power port as there is power, although reduced, even with the fuse pulled. If I get ambitiouns, i'll see if I can trace it down.

Dutch Star Don · 03-27-2017, 09:17 AM

Do you have another port with something installed in it?

Ken Gluckman · 03-27-2017, 10:09 AM

I had a similar issue, although the residual voltage was only about 2 volts. I had it fixed at Newmar and they said it was backfed through the red LED indicator on the fuse panel that tells you which fuse is blown.

PanJH · 03-27-2017, 10:14 AM

Quote:

Originally Posted by Dutch Star Don

Do you have another port with something installed in it?

Nope

PanJH · 03-27-2017, 10:16 AM

Quote:

Originally Posted by Ken Gluckman

I had a similar issue, although the residual voltage was only about 2 volts. I had it fixed at Newmar and they said it was backfed through the red LED indicator on the fuse panel that tells you which fuse is blown.

Interesting-- since the red LED for the power port did not illuminate,even when I pulled the fuse out. I pulled a few other fuses to see if it was consistent, some lit up when I pulled the fuse, some didn't-- sounds like it might be an issue with the board. I'll try to get over there today and see what I can find.

PanJH · 03-27-2017, 03:47 PM

Quote:

Originally Posted by PanJH

Interesting-- since the red LED for the power port did not illuminate,even when I pulled the fuse out. I pulled a few other fuses to see if it was consistent, some lit up when I pulled the fuse, some didn't-- sounds like it might be an issue with the board. I'll try to get over there today and see what I can find.

After thinking about this, it could very possibly a real potential electrical hazard since even with a blown fuse, power is still delivered to the device. That's a recipe for a potentially catastrophic fire.

I'll contact Newmar to get their take on this.

andyh · 03-28-2017, 07:52 AM

There is a parasitic back feed to the cigar lighterthru something which acts as a big resistor, but it can not provide sufficient current to drive anything more than a few microamps. That is why the voltmeter and the LED on the TPS power cord indicated voltage but it could not provide the current required for the TPMS operation. It is not a nice design but definitely not a fire hazard.