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Reverse lamps not working - REPAIRED!

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stolizino Avatar
stolizino Silver Member Gary Kinslow
San Antonio, TX, USA   USA
1969 MG MGB MkII "HRH Camille Of Marmite"
1969 MG MGC GT "Percival Snickersnacker"
1974 MG MGB GT V8 Conversion "Grover"
2006 BMW M Roadster "Manfred"    & more
Ignition on, reverse gear engaged, pulled the leads off the reverse lamp switch on the gearbox, multimeter indicates no juice, hence not possible to actually check the reverse switch or points beyond until I can determine why the switch isn't getting current.

Just as an aside, I noticed this problem as well as non-functioning brake lights shortly before my starter gave it up. Long story short, starter is perfect, merely needed a good cleaning on all three solenoid posts. Brake lights traced to defective switch, verified by using a jumper wire on the brake light switch connections. And my heater fan remarkably sprang to life when I noticed an errant loose wire in the engine compartment and plugged it back into what appeared to be a likely empty connector. This leave the reverse lamps.



Edited 6 time(s). Last edit at 2018-03-15 03:08 PM by stolizino.

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Swamperca Avatar
Swamperca Swamper CA
-, Nor Cal, USA   USA
1969 MG MGC GT "C-Rod"
1971 MG MGB "Rubee"
1974 MG MGB "Groovy B"
Check the wiring connector at the top of the run where it connects to the main loom. The power supplied comes from there.

stolizino Avatar
stolizino Silver Member Gary Kinslow
San Antonio, TX, USA   USA
1969 MG MGB MkII "HRH Camille Of Marmite"
1969 MG MGC GT "Percival Snickersnacker"
1974 MG MGB GT V8 Conversion "Grover"
2006 BMW M Roadster "Manfred"    & more
John, I plead ignorance.

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Swamperca Avatar
Swamperca Swamper CA
-, Nor Cal, USA   USA
1969 MG MGC GT "C-Rod"
1971 MG MGB "Rubee"
1974 MG MGB "Groovy B"
Below and aft of the fuse box about on top of the brake manifold, the wire connections on the inner fender. You probably loosened a connection while working on the starter.

stolizino Avatar
stolizino Silver Member Gary Kinslow
San Antonio, TX, USA   USA
1969 MG MGB MkII "HRH Camille Of Marmite"
1969 MG MGC GT "Percival Snickersnacker"
1974 MG MGB GT V8 Conversion "Grover"
2006 BMW M Roadster "Manfred"    & more
In reply to # 3696875 by Swamperca Below and aft of the fuse box about on top of the brake manifold, the wire connections on the inner fender. You probably loosened a connection while working on the starter.

Thanks!

Gokart Avatar
Gokart Silver Member Rob Illingworth
Palmerston North, Manawatu, New Zealand   NZL
Gary,

Did the reverse lamps work at some stage prior to you testing?

If the switch on the gear box is like the MGB one then the contact from the lever that activates the switch within the GB may not be contacting enough. There should be a fiber washer on the switch, if you remove that, then screw the switch back in, then check again. It may be that the switch has backed off or may be wearing at the contact end some.



Cheers Rob

jsrivard Avatar
jsrivard Silver Member Joel Rivard
Ramstein, Rheinland-Pfalz, Germany   DEU
1968 MG MGC GT "Maggie"
It'll be a green wire and there will be a bullet connection in-line at the position mentioned by Swamper.



Cheers,
Joel

MGC Life Blog: https://mgc.is-great.net/
MGC "how-to's" available on YouTube: https://www.youtube.com/channel/UCDMf5tRcUOG0ueyizruhv5w/

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Attachments:
ReverseLight.JPG    56.8 KB
ReverseLight.JPG

stolizino Avatar
stolizino Silver Member Gary Kinslow
San Antonio, TX, USA   USA
1969 MG MGB MkII "HRH Camille Of Marmite"
1969 MG MGC GT "Percival Snickersnacker"
1974 MG MGB GT V8 Conversion "Grover"
2006 BMW M Roadster "Manfred"    & more
In reply to # 3696941 by Gokart If the switch on the gear box is like the MGB one then the contact from the lever that activates the switch within the GB may not be contacting enough. There should be a fiber washer on the switch, if you remove that, then screw the switch back in, then check again. It may be that the switch has backed off or may be wearing at the contact end some.
That's an interesting thought. Where is the shifter lever contact? On the car itself, a single green wire and a single green/brown tracer wire, both inert, are connected to the reverse lamp switch on the right side of the gearbox. On the gearbox exploded diagram I see no shifter lever contact, only the reverse lamp switch. On the wiring diagram I see the single green wire with bullet connector between the fuse box and the reverse lamp switch on the gearbox, then the green/brown tracer wire with bullet connector from the switch to the reverse lamp housings. On the reverse lamp housing there is also the black ground wire. I see no shifter lever contact, but it stands to reason there should be something on the lever that energizes the green wire. The break is somewhere between the fuse box/shifter lever contact and the reverse lamp switch. Would I possibly also be looking for a white wire from the ignition to the fuse box?

One errant thought, when testing the green wire at the reverse lamp switch, I didn't ground it. I stuck one multimeter probe into the green wire connector and the other probe into the green/brown tracer wire connector. Maybe I should have grounded the other probe against the car instead of sticking it into the other wire?



Edited 10 time(s). Last edit at 2018-03-14 03:21 AM by stolizino.

Gokart Avatar
Gokart Silver Member Rob Illingworth
Palmerston North, Manawatu, New Zealand   NZL
The switch should look something like that in the pic. Part #20 here, https://www.ukmgparts.com/catalogue/mgc-midcat-10-submgc12-gearbox-remote-control-fittings

The two 1/4" spade fittings are obviously for the wires.

The other end has a plunger or ball down from a thread. That end screws into the gearbox where given that it is screwed all the way in the mechanisms which throw the GB into reverse press against the plunger or ball and depresses it which in turn activates the switch inside to connect the two wires thus making a circuit through to the reverse lights.

The washer, part #19, creates space and acts as a cushion between the switch ad the GB housing. If the plunger/ball (or the spring inside the switch) is getting worn removing the washer can give you a little more life out of the switch. It may be the switch is too worn out and needs replacing.

Also pays to check the plug into the reverse light fittings as they are rather loose at times and just fall off thus again making for a break in the circuit (the current goes into the fitting and then will ground out through a wire to the body or through the body of the light fitting to ground to the body through the attachment screws).

As already said if you check with a test light or meter from the green wire to the body of the car you should have power with the ignition on.

If you then put the car in gear and test between the Green/Brown wire and the body you should be able to tell if the switch works or not. If it does then the break is further down the line towards the lights. you can keep testing in this manner for power at all the connection points down till you find the fault.



Cheers Rob



Edited 1 time(s). Last edit at 2018-03-14 04:25 AM by Gokart.

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Attachments:
Reverse light switch.JPG    12.5 KB
Reverse light switch.JPG

stolizino Avatar
stolizino Silver Member Gary Kinslow
San Antonio, TX, USA   USA
1969 MG MGB MkII "HRH Camille Of Marmite"
1969 MG MGC GT "Percival Snickersnacker"
1974 MG MGB GT V8 Conversion "Grover"
2006 BMW M Roadster "Manfred"    & more
Thanks for the comments, Rob. So, there is no switch or contact other than the switch mounted on the right side of the gearbox, nothing in the immediate location of the shifter lever. Very good point about the reverse lamp fittings. I noted both are probably candidates for replaceement, as are the lamp housings themselves.

Gokart Avatar
Gokart Silver Member Rob Illingworth
Palmerston North, Manawatu, New Zealand   NZL
Gary,

I don't know C's but I know about my B and I can see by the electrical diagram in post #7 that the only switch in the reverse light circuit is the one on the gearbox that you started to test.

There is another switch on the other (left) side of the GB for the overdrive which is the same type of switch and they are interchangeable. However before you start thinking I'll simply swap them and see what happens the OD one is far less accessible. BTW these switches are commonly available and quite cheap to replace.

JIC you haven't got this already go here, http://www.advanceautowire.com/mgb.pdf

and download the coloured wiring diagrams. The one for your car is near the end. Very helpful for finding whether that stray wire should be going to the heater fan or not.



Cheers Rob

stolizino Avatar
stolizino Silver Member Gary Kinslow
San Antonio, TX, USA   USA
1969 MG MGB MkII "HRH Camille Of Marmite"
1969 MG MGC GT "Percival Snickersnacker"
1974 MG MGB GT V8 Conversion "Grover"
2006 BMW M Roadster "Manfred"    & more
In reply to # 3697189 by Gokart Gary,

I don't know C's but I know about my B and I can see by the electrical diagram in post #7 that the only switch in the reverse light circuit is the one on the gearbox that you started to test.

There is another switch on the other (left) side of the GB for the overdrive which is the same type of switch and they are interchangeable. However before you start thinking I'll simply swap them and see what happens the OD one is far less accessible. BTW these switches are commonly available and quite cheap to replace.

JIC you haven't got this already go here, http://www.advanceautowire.com/mgb.pdf

and download the coloured wiring diagrams. The one for your car is near the end. Very helpful for finding whether that stray wire should be going to the heater fan or not.

Yup, it was definitely the heater fan wire. As far as the reverse lamps are concerned, no joy on testing the green lead to the switch. So the problem is somewhere upstream. Also juiceless at the bullet connector in the engine compartment. Unfortunately, upstream is a rat's nest of green wires plugged into the fuse box and unless I want to slice open the harness sheath to find the specific wire, this is going to be painstaking unless I'm missing something obvious, as I am wont to do with unsettlingly increasing frequency.



Edited 3 time(s). Last edit at 2018-03-14 04:14 PM by stolizino.

Swamperca Avatar
Swamperca Swamper CA
-, Nor Cal, USA   USA
1969 MG MGC GT "C-Rod"
1971 MG MGB "Rubee"
1974 MG MGB "Groovy B"
Thar green wire should be getting power at the fuse box, just a short run from the connector point of the transmission harness. I'd examine all the green wires at the fuse holder.

Just looked at my car. You could also hook the green wire going down to the tranny switch straight up to the green wires at the fuse box, may need to make a pig-tail jumper wire.

stolizino Avatar
stolizino Silver Member Gary Kinslow
San Antonio, TX, USA   USA
1969 MG MGB MkII "HRH Camille Of Marmite"
1969 MG MGC GT "Percival Snickersnacker"
1974 MG MGB GT V8 Conversion "Grover"
2006 BMW M Roadster "Manfred"    & more
In reply to # 3697332 by Swamperca Thar green wire should be getting power at the fuse box, just a short run from the connector point of the transmission harness. I'd examine all the green wires at the fuse holder.

Just looked at my car. You could also hook the green wire going down to the tranny switch straight up to the green wires at the fuse box, may need to make a pig-tail jumper wire.

Bingo!

stolizino Avatar
stolizino Silver Member Gary Kinslow
San Antonio, TX, USA   USA
1969 MG MGB MkII "HRH Camille Of Marmite"
1969 MG MGC GT "Percival Snickersnacker"
1974 MG MGB GT V8 Conversion "Grover"
2006 BMW M Roadster "Manfred"    & more
In reply to # 3697334 by stolizino
In reply to # 3697332 by Swamperca Thar green wire should be getting power at the fuse box, just a short run from the connector point of the transmission harness. I'd examine all the green wires at the fuse holder.

Just looked at my car. You could also hook the green wire going down to the tranny switch straight up to the green wires at the fuse box, may need to make a pig-tail jumper wire.

Bingo!

LET THERE BE LIGHT! Rooting around the fuse box, every green wire save one was energized. The lone culprit had somehow become disconnected from the box. Reconnected it, tested it at the box then proceeded to both reverse lamp housings. Working. Woo hoo!!



Edited 1 time(s). Last edit at 2018-03-14 05:50 PM by stolizino.

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