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Odd problem, reverse light switch shorting
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johnnyvw164
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PostPosted: Fri Jul 16, 2021 1:13 pm    Post subject: Odd problem, reverse light switch shorting Reply with quote

Late last year I had the engine and trans out of my 69 Beetle. A previous owner ran over something pretty big and solid, and cracked the transmission nose cone. Fortunately these are cheap and available, so after replacing it and the trans mounts, I got everything back together. The only problem that arose was the fuse for the back up lights blows every time I put it into reverse. I checked all the wiring, there are no shorts or grounding, the switch works properly. BUT....I found if I had the trans in reverse, and then switched on the ignition, everything worked fine. It's only when it's being put into reverse from neutral that the fuse blows. It seems like something internal is happening, either within the switch or the actuator in the trans is shorting something out. Has anyone ever run across this? I'm thinking maybe the gasket for the switch needs to be thicker...it was the original one, so it may be compressed. Thoughts???
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Cusser
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PostPosted: Fri Jul 16, 2021 3:56 pm    Post subject: Re: Odd problem, reverse light switch shorting Reply with quote

Unplug the leads from the reverse switch. Use ohmmeter and see if either terminal is shorting to ground. Then put gearshift into reverse, and do same; you should get continuity between the two terminals with gearshift in reverse position.
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johnnyvw164
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PostPosted: Fri Jul 16, 2021 5:49 pm    Post subject: Re: Odd problem, reverse light switch shorting Reply with quote

Already did that...everything checks out.... I should have specified I did the "deep dive" on checking the wiring and switch. Compared to the equipment I work on for a living, a Beetle is super simple.

It's only when the switch is being activated that it shorts out. The switch is fine if the gear shift is already in reverse when I switch on the power...lights come on and the fuse does not blow.

I guess my next step will be to take the switch out so I can take a look at it for any damage that would indicate what is happening, and bench test it to see if I can replicate the problem. I was just wondering if anyone else has seen something like that that could say "yeah, here's what's happening..." LOL
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OTTO 1303
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PostPosted: Fri Jul 16, 2021 7:58 pm    Post subject: Re: Odd problem, reverse light switch shorting Reply with quote

If you have done a continuity and electrical leakage test as Cusser suggested then look at the whole reverse light system.
If you are certain that there is no continuity to ground through either side of switch, then you still cannot eliminate switch, until you eliminate everything else.

Is the backup switch the original removed from busted cone or new?

Are the reverse bulbs the correct type and rating and are the sockets in good condition?

Are connectors to reverse switch clean, snug fitting and insulated?
There is a tight fit here, if your connectors are not insulated, apply heatshrink to ensure no chassis contact. In addition, if the factory connectors were replaced at any time with a cheap crimp type, replace cheap crimp type with another cheap crimp type and SOLDER it then HEATSHRINK it.

Ensure that 12V supply comes directly from POS (15) coil post and nowhere else.
Clean and tight 12V connection to coil, fuse holder contacts clean, correct fuse (8A), feedwire to switch in good condition?
Any wire retainers in engine compartment chafing the wiring?

Disconnect wiring from reverse switch and pull up into engine compartment and inspect wiring. This section lays between the front engine bay tin and seal, over the starter, on the chassis, then to switch. Power and return wire sleeved and in good condition?

Y-connector feeding both bulbs clean and in good condition with snug connections?

Now that you have the wiring in hand, with ignition ON make contact between switch connectors by hand while watching reverse lights. Reverse lights on when connected or fuse blown?
If they light, do it several times, this will help isolate the switch as the fault.
If fuse blows, recheck everything above again, then pull the side tarboards (if present) and inspect where the wiring goes to the light assemblies.

What ya got?
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bomberbob
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PostPosted: Sun Jul 18, 2021 8:18 am    Post subject: Re: Odd problem, reverse light switch shorting Reply with quote

replace cheap crimp type with another cheap crimp type and SOLDER it then HEATSHRINK it.
I put a medium crimp on the cheap terminal, and then solder. I think it helps electrically if there is a better mechanical contact and not just rely on the solder. Also, if the terminal is going to be exposed to moisture, I would suggest using what we call "dual wall" heat shrink, which has adhesive on the inside. When you heat it up it melts and usually oozes out a little. Regular heat shrink is not waterproof, and moisture will wick into the connection and green corrosion will form. There are terminals like the Permaseal brand with an integrated heat shrink.
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johnnyvw164
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PostPosted: Mon Jul 19, 2021 1:12 pm    Post subject: Re: Odd problem, reverse light switch shorting Reply with quote

So I found the problem is that the switch shorts to ground during the first bit of movement, then when the plunger gets towards the end of it's throw it is no longer shorted. Pretty much what I expected to find, based on my previous troubleshooting. Weird....


Update: replaced switch, everything works fine now. Really odd problem.
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