Headlight switch - fried

[AUSMHLY]

Hey, smart guys...

My headlights are Lucas PL700 with SilverStar Ultra H4 halogen bulbs. 65/55 watts.

Over the last two years, the headlight switch has fried. Both were Moss replacements.

Any ideas why?

Cheers,
Roger

 

[theleisure]

Could relays solve your problem?

 

[John_Progess]

That is why I use relays on all my cars headlight wiring. Have a good day!

John

 

[AUSMHLY]

Suggestions of what relay, where to purchase, what brand, reference number and how to wire it to my brown, blue and red wires?

Thank you,
Roger

 

[Randy Forbes]

That is why I use relays on all my cars headlight wiring. Have a good day!

John

Redemtion! That's a much better idea than gluing down the trans tunnel :wink:

Yes, for those headlights (and the apparent quality of available switchgear) relay(s) are a good idea.

Run a fused line power (from starter/battery main terminal) to the relay, then use your switch to control the relay. Be certain to employ a relay with enough current capacity as the circuit will draw (plus a safety margin), or you'll be frying relays too.

As original, the lighting circuit was not fused (at least on my BN6) and I fried the whole harness not long after I bought it (4/1/1978) when the left front tire rubbed through the original dried/hard insulation and shorted to ground. When the top and side screens are in place, it's amazing how fast the cockpit can fill with smoke! Fortunately, I was at the end of my street in San Francisco and could shut off the car and coast into my driveway.

 

[theleisure]

Here's a company that's making relays for use on MGB's:

https://www.bits4brits.net/Products.html

You could easily adapt them to your needs.

Here's a thread where some customers are discussing the products:

https://www.mgexperience.net/phorum/read.php?1,1064972,1065356#msg-1065356

 

[simco]

Sound like typical British. My MGA had a glow in the dark harness. On my land rover series trucks I used Bosch dipping relays. Can't remember what the stock number was. Might have been Volvo parts. 20 amp continous. Anyway the idea is that the 2 wires out of your switch ur/uw are used in the new set up as control wires, NOT power to headlights. The power for headlights is direct from a battery source via fuse onto one leg of the relay. When the cockpit sw is turned on,power from ur sets the contacts in relay for low beam. UW for high. br is ground. If the relay is stuffed under the dash you can use original wiring to the headlight.The relay I used also was for a plug harness but regular bayonet lugs worked. If I could figure out how this computer drawing works, I could come up with a diagram. Bosch in an English car??

 

[simco]

Forgot to mention, flipping the relay on it's side shows the diagram on how it works. great for setup and troubleshooting

 

[Keoke]

"Any ideas why"?
Yes Roger, the switched current rating of the awitch was exceeded. A simple relay can eliminate this problem,.---Keoke

 

[simco]

"any ideas why"? In a perfect world,power loves to flow unimpeded. Adding "work" such as your lights on,crappy contacts, things get hot due to transfer of energy. Add 30 plus years of corrosion and there you go. Remove all your ground wires, switch input wires, clean and reinstall. You will be surprised. On other cars, you can hear the load shift of the generator with crappy wiring. With a digital tach in hundred's scale you can see the difference as well. Triumph/Mg were notorious for this.Dim headlights etc. your switch was the weakest link. Brits4 bits sounds great as it prepackaged.

 

[Keoke]

OH my goodness Power don't Flow only current do perfect world or not!--Keoke--Az- :cowboy:

 

[AUSMHLY]

Suggestions of what relay, where to purchase, what brand, reference number and how to wire it to my brown, blue and red wires?
Thank you,
Roger

So guys,
Here's a first for me. I'm quoting myself, in hopes of getting back on subject, and possible answer. :hammer:
Anyone installed one and can share how you wired it?
Roger

 

[Keoke]

Hi Roger: It depends on how much safety you think you need> I will give you a Kiss circuit and you can add on as you see fit.
1] Blue wire from switch goes to high side of relay coil.
2] low side of coil goes to chassis ground.
3] 14 AWG Brown wire goes to hot side of starter solenoid.
4] other end of brown wire goes to switched pin on relay via a20 AMP fuse.
5] Make jumper to go from switched output power from the relay back to the junction of the original blue wire and the wiring harness connection.

Any Bosh 30 AMP relay will work, Sourcing other type relays just make sure they are rated for continuous operation---Keoke

 

[anthony7777]

"Any ideas why"?
Yes Roger, the switched current rating of the awitch was exceeded. A simple relay can eliminate this problem,.---Keoke

keoke, now that is a reasonable answer, thought you waz gunna tell im to put his fuel stick in his boot and just drive his car inna day time.

 

[Keoke]

"Any ideas why"?
Yes Roger, the switched current rating of the awitch was exceeded. A simple relay can eliminate this problem,.---Keoke

keoke, now that is a reasonable answer, thought you waz gunna tell im to put his fuel stick in his boot and just drive his car inna day time.

Just didn't think of that at the time.-- :wh---- :wh---- :wh----Keoke--- :laugh:

 

[AUSMHLY]

Hi Roger: It depends on how much safety you think you need> I will give you a Kiss circuit and you can add on as you see fit.
1] Blue wire from switch goes to high side of relay coil.
2] low side of coil goes to chassis ground.
3] 14 AWG Brown wire goes to hot side of starter solenoid.
4] other end of brown wire goes to switched pin on relay via a20 AMP fuse.
5] Make jumper to go from switched output power from the relay back to the junction of the original blue wire and the wiring harness connection.

Any Bosh 30 AMP relay will work, Sourcing other type relays just make sure they are rated for continuous operation---Keoke

Hi Keoke,
I purchased this Grote relay at the local auto store, per their recommendation.

My mechanic told me this relay will not work because it will only protect the high or the low beam, not both. He said I need a relay that will do both? Your thoughts?

 

[RonMacPherson]

Not Keoke here, but let's see if I can help.


The relay is acting as a current carrying switch in a circuit. What it does is divert the current from passing through the involved switch through the relay instead.... So for every circuit PATH you wish to protect you should use a relay.

The headlight switch on most cars is primary control for the headlights. Need to remember that is only providing the power to the dimmer switch part, else you would have both high and low beams lit all the time. If your dimmer switch is strong enough to carry the amperage then no need to relay both low and high beam circuits, just the circuit going to the dimmer switch(which then selects which path for the current to flow). The AH guys here can advise on capacity of dimmer switch.

 

[GregW]

My mechanic told me this relay will not work because it will only protect the high or the low beam, not both. He said I need a relay that will do both? Your thoughts?

Mechanic=0, Keoke=1 :laugh:
Where Keoke mapped out the wiring is upstream of the dimmer switch, so the one relay would control both settings. If you wanted the extra protection for the dimmer switch, you could use two relays and interrupt the blue/white and the blue/red wires.

 

[Keoke]

Hi Roger, That is correct . However, both the High beam and the low are never on simultaneously, consequently I find no fault there . However, as I stated if you want more protection it can be added Like adding additional fuses in both legs of the headlight circuit,---Keoke

 

[Patrick67BJ8]

Hi Roger, That is correct . However, both the High beam and the low are never on simultaneously, consequently I find no fault there . However, as I stated if you want more protection it can be added Like adding additional fuses in both legs of the headlight circuit,---Keoke

They are not supposed to be on at the same time, but I have observed a very good mechanic(but electrically challenged), hook them up to work at the same time. He thought it was cool. They really was bright right up until the time the smoke escaped from the wires.
No, it wasn't me and I promised(the guilty party),not to ever tell who it was.
Patrick