Headlight fuses

I've been studying the wiring diagrams for my '70 MGB convertible. Neither the Advance Auto or the factory diagrams show a fuse for the headlight circuit. Am I missing something?

you're not.....the car is...no headlight fuses.

Ok..... That's what I thought. As I redo the wiring this looks like an opportunity to improve things.

when i reworked my headlights i switched mine to run thru relays directly off the alternator and installed a modern auxillary fuse block and used resettable breakers for the headlights. turned out great and my lights are brighter than ever

That sounds like what I'm planning. Relays, protected circuits, all of that. Just had a hard time believing that there were never any fuses on the lights originally. Or some of the other circuits for that matter. Lots of wires running around that could have grounded and made a disaster.

Check this out
http://www.bits4brits.net/
Best money you'll ever spend. Your lights will be brighter and you'll save yourself from having something go up in flames.

FYI on my car anyway....i re-did mine due to the ground connection developing high resistance. they are now directly grounded to the frame. there is a sneak path for ground thru the starter windings so if you lose your headlight ground when you try to turn them on it makes the starter engage. Happened to me and have heard it has to others as well. it was while i was addressing this that i did the whole relay mod since the lights just werent that bright anyway. now people flash me to dim my lights even when im on low beam. have to show them if they dont like that brightness, they sure aint gonna like the alternative...lol. I'll gladly take pics and show you but if you search my name here you should find my post about it

ok so my pics were posted too long ago to search...let me know and i will take pics of how i did mine and send to you...just pm me

Protection may well depend on where you put the fuse, plus, many cars do not have fuses on headlights, as if the fuse blows it could leave you in a bad way.

Some cars had a self resetting thermal overload type fuse/switch, if the circuit got hot, it would cut out then come back on. I would guess current cars have solid state protection and of course relays, perhaps relays on the relays. ;-)

The PO in my car put a fuse in the wire for the fan, but just by the fan, the wiring running up to it ran off the starter and was running un-fused over a number of sharp edges, I enclosed it in split plastic conduit from Home Depot.

Enough people have worked on my car that the wiring is confusing and questionable in a number of areas, this year's project include changing a number of things, cleaning up splices, plus a covered post to jump or charge the battery from the engine compartment, and also to work as a primary source for relays to run anything new and the lights, horn, etc. via relays.

There are a number of added wires already on the starter, plan is to provide a convenient starting place where meaningfully located fuses also have access.

I suppose you could add a fusible link at the battery and wire a lot of stuff off that that you want protected, there are more than a few wires on the MG and a lot of other cars that are not fused.



Regards, John

[color=#FF0000]Check this out
http://www.bits4brits.net/
Best money you'll ever spend. Your lights will be brighter and you'll save yourself from having something go up in flames.[/color]


I bought one of the "Limey" kits and was installing that when I noticed that it doesn't seem to address the headlight fuse situation either. It splits some circuits from the original fuses, and adds relays to some circuits, but I don't see whare it adds protection to the headlights.

I was thinking about having a separate fuse and relay for the high and low beams. Of course other circuits as well, but that was what I was planning for the lights. If I had sudden loss of one circuit, I could use the other to get off the road. The auto reset circuit breakers are another option in place of the fuses.

dave thats exactly how mine are...separate circuits for high and low...via auto reset breakers...you will see in the pics i send you later

If I read it correctly, the bits4brits wiring diagram for the horn/headlight circuit has one 20 amp fuse for everything. I know the arguments about whether to fuse or not, in case the fuse blows as another weak point in the circuit, but surely one fuse for both low and high beam circuits is very dangerous. At the very least wire the relays seperately with two fuses. If one blows you can switch to the other beam rather than crashing in the dark !!!

The omission of the fuse on the headlamps was intentional. I don't agree with that decision, but it was a feature of the design.

I would recommend using a self-resetting circuit breaker on the headlamps. It is true that such a breaker drops the voltage by a couple of tenths of a volt, but I find it to be negligible and unnoticeable. If an intermittent short appears (say a wire vibrating against a sharp piece of metal) it will trip, and then reset a few seconds later. If a fuse blows, you are in the dark until you come to a stop and change the fuse.

I have a relay and fuse for each bulb, per the set up in Rick Astley's book. If the fuse for one bulb blows, the other side is still working.
Cheers,