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Discussion Starter · #1 ·
Hi.

So today I decided to see why the reverse sensors are not working on my new ('96) Swift Royale (Ducato based). Switched ignition on and no reverse light! That's the problem, me thinks, so I set about changing the bulb . . . . . new bulb doesn't come on!

Out comes the tester and with no bulb in the holder, it shows 4.5V but put the bulb in the holder and the voltage drops to 0V.

I assume a problem with the reverse sensors, so I disconnect the whole lot. Now the holder shows a healthy 12V but still drops to 0V when I put a known working bulb in.

I can't fathom what the problem is and I'm at the end of my knowledge so can anyone please suggest what the issue can be and how to sort it please.

Oh, and with a bulb in the holder, a "Continuity" check, sets the meter to 0.00 (Which means there is continuity between -ve & +ve via the bulb fillament but no voltage.

Thanks
 

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Re: HELP! - Reverse light Shows 12v without bulb & 0V wi

Double-Entendre said:
Hi.

So today I decided to see why the reverse sensors are not working on my new ('96) Swift Royale (Ducato based). Switched ignition on and no reverse light! That's the problem, me thinks, so I set about changing the bulb . . . . . new bulb doesn't come on!

Out comes the tester and with no bulb in the holder, it shows 4.5V but put the bulb in the holder and the voltage drops to 0V.

I assume a problem with the reverse sensors, so I disconnect the whole lot. Now the holder shows a healthy 12V but still drops to 0V when I put a known working bulb in.

I can't fathom what the problem is and I'm at the end of my knowledge so can anyone please suggest what the issue can be and how to sort it please.

Oh, and with a bulb in the holder, a "Continuity" check, sets the meter to 0.00 (Which means there is continuity between -ve & +ve via the bulb fillament but no voltage.

Thanks
To me it sounds like an earthing fault. Have you tried temporarily by passing the -ve wiring by putting in your own earth to the chassis. On a vehicle of your age the connections may be not as good as when it was built.

Derek
 

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Discussion Starter · #3 ·
Thanks for that and I can see where you're going with it but it is a "Common" Earth / -VE for all the light cluster and the tail lights read 12V, as do the indicators and the stop lights, so I'm not sure it is an earth issue.

any other ideas folks?
 

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A poor earth can mean that some bulbs will work and some not. I have followed many a Ford that when the brakes are applied some lights go out 8O 8O
 

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A very usefull tool to help figure out what's going on with this sort of fault is a simple test lamp:
Bulb holder (with working bulb in!); one lead to a croc. clip, and the other to a probe.

By connecting the croc. clip end to the chassis (0v), or to a known 12v, you can reliably test for voltage or earth at each point in the circuit, with / without reverse gear selected.
Because a volt meter has such a high resistance, it can give you 'mis-leading' results, whereas a test lamp will either be 'on' or 'off'.


Also, clean & re-connect any connectors in the circuit, corrosion here can often be the cause of faults.

Good luck.
 

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I have exactly the same problem and have not yet resolved it, but will get it fixed when I get it serviced and MOT'd in August (yes, I know that reverse lights are not part of MOT)

They suggested an earth fault but it is all on the same plate (indicator/brake/rear) so must be a bad connection from the reverse light switch on the gearbox - you need long arms to get at it - through the wiring to the lamp cluster. I can't trace the wiring so will leave it for now. It's just annoying......
 

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Discussion Starter · #8 ·
Thanks again folks.

now I'm on this "Reply page" I can't remember all the points to reply to but I'll give it a go:

1. my "Contacts" are like new in the light cluster but I reseated them just for good measure.

2. I was the owner of a ford escort with the disco rear lights - problem being a corroded earth that furs up and grows to met another contact - mine on the MH are all spotless.

3. The stop bulb is a single filament, separate to the tail bulb.

4. If it was a problem with the +VE from the reversing switch, why does it show 12V without the bulb in? and 0V with a bulb? and 4V with the reverse sensors attached?

5. I thought the Reverse Light WAS part of the MOT? (My van passed 10 days ago, hence my panic - can anyone confirm if it is a testable item?)

I'll try the "Add a new earth" option tomorrow but I really can't get why the voltage drops to 0V with a bulb in the holder?

thanks folks, thus far

Keep the suggestions coming and I'll keep you posted - seems like I'm not the only one!!!!!
 

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Hi,
If you have a poor connection you can have 12 volts showing but as soon as you try to draw any current e.g. a bulb,the voltage will drop due to the high resistance at the bad connection,my money would be on the switch, with very long arms try bridging it out, best of luck,
Regards,
Chris
 

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This is another one of those electrical problems where a digital voltmeter is not your friend. Why? Because it doesn't draw any current through the circuit. (actually it does but it might be a millionth of an Amp) So if you measure an open circuit (bulb removed) it almost doesn't matter how much resistance (badly corroded contacts etc) is between the measuring point and the battery voltage you will still measure the battery voltage.

I know to a non electrically trained person this doesn't sound right but its true.
 

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Discussion Starter · #11 ·
stickey said:
Hi,
If you have a poor connection you can have 12 volts showing but as soon as you try to draw any current e.g. a bulb,the voltage will drop due to the high resistance at the bad connection,my money would be on the switch, with very long arms try bridging it out, best of luck,
Regards,
Chris
Chris, thanks, your suggestion is one I've not tried, though as a total electrical-muppet, I'm not sure just what you mean.

Would you please explain just what I have to do. It's the "Very long arms, try bridging it out" bit that I'm struggling with. Where will i find the switch and what does "Bridge it out" mean (Sorry for being so thick ;-)

Thanks
 

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Discussion Starter · #13 ·
Jezport said:
My bet would be that there is a bad connection or water in the junction box which connects the conversion part of the motorhomes wiring to the base vehicles wiring. Or if towbar electrics have been fitted look there also.

If you enter your location in your profile someone near you may be able to help.
Oh, Man!

Where would I start looking for the junction? Yes, there are towbar electrics (Though not connected to the reverse light)

I'm in Sheffield, S. Yorks, if anyone is near?
 

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Discussion Starter · #15 ·
Jezport said:
You follow the cabling back and I would think the first junction will be the one where the electrics split to supply the towbar. check here first then work further up line.

I am in north Leeds, if you are passing I dont mand having a look.
Jezport, I thank you kindly Sir, for your offer and if I can't make it right over the next week or so, I'll PM you and hopefully take you up on your offer.

The Towbar electrics are all soldered directly to the wires on the rear light cluster on the opposite side to the reverse lamp and all seem ok, connection wise. I'll spend today giving all the suggestions a check but I need to know where the reverse switch is located and how do I access it?

Thanks again y'all
 

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Hi,
This is what I would do....somewhere on your gearbox there should be a switch with two wires connected to it, one will be a supply wire from the fusebox the other will go to the reversing lights, the switch will be in the form of an object screwed into the gearbox casing, the only other thing screwed into the gearbox casing is the speedo sensor(depending on age of vehicle) on my van the switch you want is at the front but it is not easy to see. Hoping that you can get test meter probes to the switch :roll: switch on ignition, select reverse and test VOLTAGE between each switch terminal and earth with a bulb in the reverse lamp and again with no bulb. If you lose the 12 volts on one side of the switch but not the other when a bulb is in the lamp then it has to be the switch, if you lose the 12volts from both sides of the switch with a bulb in then the bad connection has to be from the fusebox to the switch. If you get a healthy 12 volts on both side of the switch it indicates a bad connection between the switch and the lamp. NOW it is possible that the reversing switch operates a relay to turn the reverse light on and off but at this stage you need an auto electrician familiar with your base vehicle,
let me know how you get on,
Regards,
Chris.
 

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Discussion Starter · #18 ·
duxdeluxe said:
The reversing light is not mentioned in the MOT Test Manual so it should not be a failure item.

Thanks for the above explanation on voltages - I just need long arms to get at it
Where is it? Where is it??????????

Where is that reversing light switch located PLEASE!!!!

My latest testing shows the following:

1. Connect a test light - does not light
2. take a +VE feed from the sidelight to the reverse light . . . . hey presto, it comes on!
3. The Reverse light +VE still shows 12V until you connect any sort of bulb

What does this all mean?
 

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Hi, you may be better of combining your two topics or at least just use one of them, because they are basically the same problem.

The answer to:
3. The Reverse light +VE still shows 12V until you connect any sort of bulb What does this mean?

As has been explained in previous replies it means there is a high resistance in the circuit i.e the fuse, the switch or the wiring connections.
Without the bulb you are not drawing current and you are measuring the open circuit voltage. When you put the bulb back in it completes the circuit BUT the volts is dropped across the high resistance leaving none at the bulb. Say the reversing switch has poor contacts inside it. The voltage will pass through the contacts without the bulb but be "dropped" across the contacts with the bulb inserted.
 

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good tests and makes things clearer.

You did say you were electrically challenged so I'll talk down to you if that's OK ?:twisted:

What it means is the cable feeding the 12V to your reverse light has some corrosion somewhere and the energy (current) needed to light the bulb is being used up in the corrosion and not in the bulb. The meter you are using will still read the 12V at the lamp fitting as it doesn't need much energy to work.

As a 12V feed from the tail lamp in your test does light the reverse bulb you have proved the earthing is OK from the lamp fitting to the chassis. So this leaves the cable TO the lamp fitting and the first culprit will be the reverse switch.

This will be located by the gearbox so it'll get activated by the action of selecting reverse, look for a sticky out thing with 2 wires on it !.

Sadsack
 
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