Fuse #7 keeps blowing and speedometer dies

[MTB_TDI]

I am having an issue with my MK4. It mostly happens when the car is warm. The speedometer works until I switch the car into reverse and it blows the fuse. It doesn’t happen first thing in the morning, but after I drive it for a while. I’m trying to find the short but need some advice on where to look.
Any advice would be greatly appreciated.

 

[eddieleephd]

I would pull the plug to the reverse sensor when it happens and see if it or one of the wires are grounded.
Of course, if you unplug the reverse sensor and it doesn't happen when you shift to reverse you know it's that circuit either way.
It's likely a grounded wire from the reverse sensor, or in the light circuit that goes to the backup lights. Ones rubbed through and shorting when it gets hot.
There's a possibility that it's the switch/sensor shorting to the trans also. That would be an easy fix, replace the sensor.

Basically you have constant power to the sensor/switch and when you shift into reverse it closes turning the backup lights on.

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[WildChild80]

Have you done any major work lately? Like bad the trans out of anything on the driver's side or inside the dash, has the dash been out for a heater core replacement?

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[MTB_TDI]

Transmission was out about a year ago when I put in the SB clutch. I replaced my ignition lock cylinder and switch a few weeks before the short started happening. I'm going to do some unplugging of the reverse lights, reverse switch, etc and see if this stops. I'll post up here when as I go.

 

[wonneber]

From my notes:
Fuse 7. Back-up lights, speedometer vehicle speed sensor (VSS) (10A).
The speedometer works before backing up so I'm inclined to think its in the wires going from the b/u switch to the back of the car.

I would unplug the b/u switch and use an amp meter to confirm it's drawing more then 10 amps.
If not then check for the switch grounding internally with the car in reverse. Long shot.

 

[eddieleephd]

It could be a bulb shorted out within itself. Unlikely, but possible.

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