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'85 MY TE Reversing lights (not) - Interior/Exterior/Lights/Glass/Alarms/ICE/HVAC - The Lotus Forums #ForTheOwners Jump to content


'85 MY TE Reversing lights (not)


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  • Gold FFM

Hi all,

Why might I only be getting 3.84V from the reversing light switch ? does it mean the switch itself is knackered, or might there be some other reason ? I have cleaned and emery'd the contacts on the switch.

Not being an expert, I would have thought the switch either works or not ? Is this not the case? I not, please could someone explain the physics to me ... ?

I only noticed some voltage when replacing bulbs with LEDs. V.small light with low voltage, but clearly not enough to drive  fliament bulb ...

TIA,

 

 

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Apparently, a bit of the smoke from the wiring has escaped. You need this:spacer.png

 

 

++++++++++++

 

More seriously, obtain a multimeter.

 

With the transmission reverse switch disconnected, measure the resistance or Ohms (on the lowest scale possible) across its contacts. Should be  INFINITE (some meters display "1").

 

Then select reverse on the gearstick, and take more readings. Should change the state to ZERO (less than 0.5 ohm) .

 

If the reading doesn't change between forward and reverse, it's the switch. (IIRC not uncommon).  If the switch readings are as described, we will dive into the wiring.

 

++++++++

 

An alternate check would be to measure VOLTAGE with the ignition ON.  You should have within one volt of the battery voltage, measured between one or the other of the contacts, to the trans case.

 

Post back with results.

 

 

 

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Atwell Haines

'88 Esprit

Succasunna, NJ USA

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  • Gold FFM
10 minutes ago, CarBuff said:

Apparently, a bit of the smoke from the wiring has escaped. You need this:spacer.png

 

 

++++++++++++

 

More seriously, obtain a multimeter.

 

With the transmission reverse switch disconnected, measure the resistance or Ohms (on the lowest scale possible) across its contacts. Should be  INFINITE (some meters display "1").

 

Then select reverse on the gearstick, and take more readings. Should change the state to ZERO (less than 0.5 ohm) .

,If the reading doesn't change between forward and reverse, it's the switch. (IIRC not uncommon).  If the switch readings are as described, we will dive into the wiring.

 

++++++++

 

An alternate check would be to measure VOLTAGE with the ignition ON.  You should have within one volt of the battery voltage, measured between one or the other of the contacts, to the trans case.

 

Post back with results.

 

 

 

Thanks @CarBuff , I have a multimeter - and am getting to know how to use it effectively...  I did this voltage check, which is where I got 3.84V, but this was across the two terminals on the switch itself ('cos I thugh this was logical). I'll repeat same with your advice with a contact to the transmission casing (tomorrow in daylight seems good),and post back what happened ...   appreciate the assistance ...  

 

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3.84 volts across the switch seems like quite a drop. Disconnected, you should have 12V plus  on the  Green(?) side with key on, and bulb resistance to ground on the other. If you jumper the two wires with the key on your lamps should light up. These switches can get bashed up when pulling the engine/transaxle assy, so check how secure the flag terminals are on the switch body.

image.thumb.png.0a8337afa162d355e9a20226ef4f7a86.png

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  • Gold FFM

I disconnected both wires at the switch, and took measurements without reverse engaged - multimeter value was 1. Put it into reverse, and the multimeter value was 1. ( @CarBuff - so this should be a new switch?)

I then measured voltage at the switch grounded on the trans case, and got 9.3-9.4V.

Can these two conditions co-exist  - voltage but no switching? sounds illogical, perhaps I've taken the wrong readings ?

Finally, I did a continuty test on all the wiring from the supply to the lamps to ensure no corroded wiring in the loop:- Each of live and ground to both lamps through all the wires - no continuity issues were observed.

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A "1" on the ohms/continuity setting indicates an open circuit on most multi-meters; that would be a bad switch if you're on the right setting.

9.4 volts (assuming 12+ at the battery) tells us that either the wiring to the switch has a bad connection or other resistance, or that the grounding strap from the transaxle/engine to the frame & battery is bad. Check the resistance from your trans case to the negative of the battery first as that's easiest. Should be very small ohms resistance.

9 volts should still light up the bulbs a bit if you connect the two switch wires together?

-We told you this car would make a mechanic out of you-

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  • Gold FFM

thanks @snowrx, the new "LED" bulbs do light up - barely visible. Filament bulbs don't illuminate at all.

This is why I'm confused - if there is voltage then how is some voltage leaking to the bulbs if the switch has failed ? maybe I need a bigger cannister of @CarBuff's smoke 😂

 

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I'm confused also!

I just put a bunch of different bulbs on a power supply, and the incandescents start glowing fairly well at about 5 volts, so I'm wondering why they don't glow for you. With the LED's most of them are at least half lit at 9v, except for a few of the "CAN-safe" bulbs with the resistor on them which barely start at 8V.

If bypassing the switch won't make them work there's more going on.

You might want to check the voltage at both sides of the fuse (19 on my diagram, probably different for UK model, maybe #8) and the green wire at the RHC Rear Harness Connector (if you have one) to see if you have 12V at either point. That could help locate the voltage drop. Most of the early domestic wiring diagrams show the reverse light on the same fuse as the hazards, fed from the white wire off the ignition switch, so it might be different than the US/Federal diagram I posted. The white wire runs the fuel pump so if you're running it's probably feeding the fuse box 12V OK. Do your hazards work?, they may run off the same fuse.

Then measure voltage right at the bulb socket pins,  then with power off measure resistance from the socket shell to your battery negative. Somewhere there is a fault, or prior owner malfeasance. 

 

-pardon the 8 time zones between replies-

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9 hours ago, snowrx said:

Most of the early domestic wiring diagrams show the reverse light on the same fuse as the hazards,

Hmmm... perhaps actuating the hazard switch 12 to 15 times will clean its contacts. Common advice when turn signals don't work...

 

Costs nothing to try. Let us know if that changes anything.

Atwell Haines

'88 Esprit

Succasunna, NJ USA

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  • Gold FFM
2 hours ago, CarBuff said:

Hmmm... perhaps actuating the hazard switch 12 to 15 times will clean its contacts. Common advice when turn signals don't work...

 

Costs nothing to try. Let us know if that changes anything.

Hi @CarBuff , all other exterior lighting works fine ..   inc. hazards and indicators .... - have also "activated"  hazards many times - (I now do this about once a week - thanks to prior threads)  - am just about to go back out under the rear and start the revised (extended) check list again, just so I can get to the nub of the problem.  🙂 

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Sorry if I speak of something already addressed here but have you tried direct connecting the green feed wire to the green/brown reverse lamp feeds? The lamps themselves should serve as continuity testers, leaving off concerns for voltages measured may certainly simplify the effort. Of course this presumes adequate voltage on the green and clean ground at the taillamps. On that expect 12+ volts on the green feed, key on engine off, if measured to solid ground.

Cheers 

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