Lights cut out suddenly

[BrianS]

Gents..can anyone out there help?

I have a 1973 130/5, which has a disconcerting habit of plunging itself into darkness. What seems to happen is this....with the heater on, all will work well until there is a faint click (as if from a relay) and all the lights cut out, completely. The headlamps drop back into their pods, the sidelights go out, the lot. After a few minutes, everything springs back into life! With the heater off, there isn't a problem....

Any ideas/suggestions very gratefully received!!

BrianS

[types26/36]

Brian, type "thermal cut out" into the search box .....top right side....then search.....you should get a few threads to read

[Robbie693]

Very common.

As Brian says, there is a thermal cut-out in the light circuit. It's a black plastic thing usually next to the light switch. When mine played up I bypassed it with a fused wire temporarily, then eventually fitted relays into the headlight circuit thereby taking the heavy loads out of the switch. At which point I re-connected the the thermal thingy and it's been fine since. The problem may have been caused by me having 60/55W halogen bulbs fitted.

The relays are a good idea anyway and gave the added benefit of making the lights brighter!

Hope this helps

Robbie

[BrianS]

Thanks, Brian and Robbie, those points look really helpful!!

[elansprint71]

Do you mean heater or heater fan?

[BrianS]

Pete, hi.....originally, it was the heater fan that seemed to trigger the problem....in other words, when the dash had got really hot. Now it occurs when the un-fanned heater has been on for a while.

Brian

[J.E.S]

Agree with Robbie most likely cause is the thermal cut out attached to the back of the dash close to the light switch. If you have uprated headlights (and have been using high beam) more current will flow and the wires get hotter until the cut out cuts out plunging you into darkness (which I can testify is disconcerting when doing 60 down a country lane). Quick fix is to replace the cut out with a suitable fuse, long term relays are a good idea.

John.

P.S. Unlikely to have anything to do with the heater fan.

[BrianS]

Thanks, John...much appreciated.

Brian

[AussieJohn]

My car had two thermal cutouts, one for headlights and one in the sidelight/dashlight circuit. I put 3 relays in for side, low and high beam then reconnected the cutouts, no problem for a few years.

[Galwaylotus]

My car had two thermal cutouts, one for headlights and one in the sidelight/dashlight circuit. I put 3 relays in for side, low and high beam then reconnected the cutouts, no problem for a few years.

...and then what happened?!!

[AussieJohn]

Hi Galway, and then it burst into flames and went to that Lotus heaven in the sky; just kidding, it hasn't any problems since [ other than a minor mechanical issue; a valve head decided to visit a piston which wasn't a pretty sight.]