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reverse lights wiring
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Spaniard66
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PostPosted: Thu Oct 18, 2018 6:52 pm    Post subject: reverse lights wiring Reply with quote

Hello, I installed a set of Hella reverse lights on my beetle, and wired them up with an in-line fuse to one of the terminals to the reverse switch on the transmission, and the other terminal wire was split to cover both reverse lights. I ran new wiring and terminals. The in-line fuse is blowing out as soon as a shift into reverse.

Lights will not even flicker. I am using a 7.5 amp fuse and even tried a 20 amp fuse,, same result. fuse blown upon switching trans into reverse. I am getting a 12.3 volt reading from the coil connection before reaching fuse.

It is an aftermarket trans, and of course 12volt.

Any suggestions?

Does the reverse light switch have a power in/out side ? two terminal switch
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Cusser
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PostPosted: Thu Oct 18, 2018 7:29 pm    Post subject: Re: reverse lights wiring Reply with quote

Spaniard66 wrote:
Does the reverse light switch have a power in/out side ? two terminal switch

No, only power to that switch is from coil positive terminal #15. It's just a contact switch.

Your job will be to determine whether the wire to the switch is shorting out, whether the switch itself is shorting out, or whether the short is once power leaves the switch to go back to the bulbs/bulb sockets.
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mukluk
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PostPosted: Thu Oct 18, 2018 7:30 pm    Post subject: Re: reverse lights wiring Reply with quote

The reverse light switch is a spring loaded plunger type momentary on switch -- so long as the reverse selector is in contact with the plunger and holds it in, the switch contacts are closed and complete the circuit. As soon you shift out of reverse, the selector moves away from the switch, the plunger springs out, and the contacts open.

Since the fuse doesn't blow until you shift into reverse, we can safely say the power wire from the coil to the switch is good. We can further safely assume the plunger is working and closing the contacts when positioned by the selector. Either the output terminal of the switch is shorted to ground, the wiring from the switch to the light assemblies is shorted to ground, or there is a short to ground of the lamp power wire in one of the assemblies.

A volt/ohm meter will be useful here to determine where your short to ground is located.
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Spaniard66
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PostPosted: Thu Oct 18, 2018 8:03 pm    Post subject: Re: reverse lights wiring Reply with quote

Thank you, since the lights were used items, I will check those first to make sure they are in working order. I purchased a new reverse switch and will replace at the end.
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KTPhil Premium Member
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PostPosted: Thu Oct 18, 2018 11:53 pm    Post subject: Re: reverse lights wiring Reply with quote

I had the same problem and it was an internally broken reverse switch. A new one fixed it right up. I suspected this after checking wiring with a VOM-- no shorts, so the switch was the suspect.
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ashman40
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PostPosted: Fri Oct 19, 2018 5:22 am    Post subject: Re: reverse lights wiring Reply with quote

Remove the wires from the reverse light switch on the transmission. With your multimeter test the resistance between each terminal of the switch (one at a time) and the ground strap of the transmission. Move the shifter into reverse and test the terminals again. You are testing if the switch is internally grounding out. AT NO TIME should there be continuity to ground from either terminal of the switch. If you have a path to ground you have a bad switch. Replace it.

Next, confirm the switch closes when the transmission is placed in reverse. With the car in neutral, test the resistance between the two terminals of the switch. There should be infinite resistance (open circuit) when not in reverse.
Shift the transmission into reverse. Test the terminals again. Now there should be (near) zero resistance between the two terminals.

Of the two wires that make it to the reverse switch, one will be the INPUT providing power (12v). The other is the OUTPUT and runs to the reverse lights.
With the ignition switch ON test that one of the wires has 12v.
For the other wire, remove the two reverse light bulbs from the taillight housing and then test the wire for continuity to ground. Without the bulbs installed there should be an open circuit (infinite resistance to ground). If you have a low or near zero resistance with the bulbs removed you have a short in the lighting wire somewhere. You will need to trace this down. Find the Y-split in the engine compartment where the one return wire from the switch turns into two. Separate the wires and test all three wires separately to determine which is grounded.


Spaniard66 wrote:
I installed a set of Hella reverse lights on my beetle, and wired them up with an in-line fuse to one of the terminals to the reverse switch on the transmission, and the other terminal wire was split to cover both reverse lights. I ran new wiring and terminals. The in-line fuse is blowing out as soon as a shift into reverse.

I'm confused by your description.... Confused
There are two wires running to the reverse light switch. One is the 12v INPUT wire which comes from the ignition coil. The other is the OUTPUT wire which runs to the reverse lights.
I read the above to say you have wired your NEW reverse lights to the INPUT wire and NOT the OUTPUT wire. This would mean your reverse lights would turn ON when you turn ON your ignition switch???
Since you have NEW reverse lights and wires... what have you done with the stock wires? The original black wires that ran from the reverse switch to the Y-split to the left and right reverse lights in the taillight housings. Where are these now? Are they somehow grounded? If so they will short out the circuit as soon as you shift into reverse. If you are not using these wires, wrap them in electrical tape to prevent an unexpected ground.

If I were adding new (stand-alone) reverse lights I would make use of the existing reverse light wiring. Just tap into the black wire at the junctions one the left/right sides of the engine. The 8A fuse in the stock inline fuse can just support four (4) 21W reverse lights. 21W x4 = 84W = 7A @12v.
If you don't want the reverse lights in the taillight housings to turn ON, just remove the bulbs but leave the wiring in case you want to go back to stock.


Good luck finding your short.
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Cusser
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PostPosted: Fri Oct 19, 2018 6:11 am    Post subject: Re: reverse lights wiring Reply with quote

Thanks, Ashman40 for providing detailed instructions for him.

So many folks apparently have so much trouble with simple wiring issues, and you're WAY more patient and also better than I at explaining in writing.
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sjbartnik
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PostPosted: Fri Oct 19, 2018 7:49 am    Post subject: Re: reverse lights wiring Reply with quote

Hey man if you're blowing a fuse as soon as you put it in reverse, you have a dead short to ground somewhere.

DO NOT simply replace a fuse with a higher rated fuse. You can easily figure out roughly what the current draw for the reverse lights should be, it's 2 21w bulbs at 12v, so 42w. 42/12 = 3.5A. An 8A fuse is more than sufficient for the electrical load of the reverse lights. A higher-rated fuse just means you're more likely to fry the wiring before the fuse blows. The fuse is there to protect the wiring from overload.

ashman40 gave good instructions (as always). The only thing I wasn't clear on from your original post is where did you source the 12v power to feed to the reverse light switch? VW originally did it by running a wire from terminal 15 on the ignition coil (with an 8A inline fuse).
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Spaniard66
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PostPosted: Fri Oct 19, 2018 4:45 pm    Post subject: Re: reverse lights wiring Reply with quote

Thank you all who replied.

Special thanks to Ashman40, his detailed information helped me diagnose and find the problem

It seems the reverse light housing was grounding itself to the incoming power wire.

I also had to redo my splice point, as my connection point was not done correctly. My 61 never had reverse lights and there was no preexisting wiring for reverse lights.


Both lights are up and working perfectly, with no burned wires or fuses. Very Happy
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ashman40
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PostPosted: Sat Oct 20, 2018 1:15 am    Post subject: Re: reverse lights wiring Reply with quote

Good troubleshooting! Now take her out and drive! Very Happy
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'67 Beetle #2 {2019 project car - Wish me luck!}
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