OK, before we start, let’s get the obvious out of the way. I made a stupid mistake. Don’t know how I did it but it happened. Appreciate any suggestions. This is a 70 S2.
So my e-type was sitting at a garage for several months with a battery that I knew was getting increasingly weaker. The garage didn’t have an electrical outlet for a tender and I didn’t have a battery disconnect.
I went to start the car and knew I was going to have trouble so brought a spare battery with me to jump it but the battery in the car was so dead that even the spare battery jump wouldn’t get it to turn over enough. No problem my friend was there with a newer BMW and we backed the car out of the garage and proceeded to hook up a set of high quality jumper cables. This is where my mistake comes in.
Unfortunately I was talking to her at the same time I was placing the jumper cables on my battery terminals in the Jag… AND GOT THEM REVERSED! I had put the positive on the negative battery terminal and the negative on the positive battery terminal in the Jag and then proceeded to hook them up to her car. I was wondering why the car wouldn’t turn over and got out of the Jag and was looking at the engine and waiting a little bit so the battery could charge up. This is when I saw some smoke emanating from the alternator, which is the original type of alternator. Not a one wire.
Realizing my mistake, I pulled the jumper cables off the battery while I screamed in anguish at my stupidity. I waited a couple of minutes for things to calm down and then decided nothing from nothing leaves nothing and proceeded to correctly hook up the cables and then jump started the car.
Miraculously, the car started and ran fine and the alternator was reading a healthy charge going into the battery. Seemingly nothing was wrong. I decided to drive the car home and then go get a new battery and put a battery disconnect on that new battery.
Now this is where I need help. I got the new battery installed and everything seemed fine. I was checking all the systems and realized that though the turn signals and running lights worked, the headlights we’re not coming on. So the question is, what do you think the potential issue could be with the headlights? Could it be as simple as a fuse? Could it have burned up the relay? I’m going to be jumping into the car today to start diagnosing things but I thought I’d ask this august group what they thought could have happened.
As smoke came out from the alternator, I would suspect of burn diode(s) in the rectifier (At least in S3 rectifier assembly is in the alternator) , that could have caused higher that expected output voltage, a cause for blowing a fuse - therefore headlights are a consequence and not a cause. Or a coincidence.
For S3, rectifier testing using an ohmmeter is described in the workshop manual procedure 86/10.08/1 (i can send a photo if needed) . Meanwhile you can also check if the alternator output does no go over 12.7 V or so at higher revs.
Good luck !
ok, so I poked around and it looks like the fuse for the high-beams was burnt. Replaced it and the high-beams work fine now. The low-beam fuse looked ok but the low-beams wont come on. Replaced the fuse and it’s the same. No low beams.
From outward appearences and the voltage gauge in the car, the alternator looks the same as before, which is to say good. All other lights/systems appear to be working fine. The high beams are about half as bright as modern low-beams so I’m fine if caught out in the dark but I’d like to figure out whats what at some point…
To the OP, just asking a question regarding the replacement 35 Amp high-beam fuse - did you replace it with a British fuse or other, i.e. you are familiar with British vs. American fuses, right Mr. T?
The Amps are the same but the fuse ratings are different. American fuses are rated for the safe carry current, and the blow current is about 1.5 times that much. British fuses are rated for the blow current, so an American 25A fuse is about the same as a British 35A fuse. That said, the rating is not that critical. In a house, the fuse or circuit breaker is designed to open if someone does something dumb like plugging two hair dryers into the same circuit. You can’t do that in a car. In a car each fuse circuit is designed to carry a certain amount of current and will never carry more than that under normal circumstances. The only purpose of a car fuse is to interrupt the current flow if there is a catastrophic failure such as a short circuit. In other words, the fuse will either carry it’s designed current forever or will blow when 200 Amps tries to flow through it during a short. Therefore the fuse only needs to be the weakest link in the system, with a smaller internal wire than the wire it feeds. A 25 Amp or a 35 Amp fuse will both blow equally fast when faced with a dead short, so putting an American rated fuse in a British car will not be a problem.
British and American standards for rating electrical fuses are different. Both provide an “Amp Rating” for very similar looking fuses, but the two ratings mean very different things. The US system rates the fuse based on the continuous load it can handle for a specified period of time w/o blowing, whilst the British system expresses the load at which the fuse will immediately blow.
Details expounded upon in attached to include a correlation table comparing British and US fuses
Thanks, I’ll order some “British” fuses. The fuses in the car are Lucas with little paper tags w “Lucas” and the rating on them inside the glass tube. Seems incredibly intelligent to put a flammable substance inside a glass tube with a red hot filament…
I had this same issue one night and was hundreds of miles from home. High beams were fine, low beams were flickering and then would not come back on. Since I was driving mostly during the daylight hours it was not a problem. At home I began troubleshooting the lack of low beam and found the toggle switch was not working for the low beams. I tried to repair the switch, but some internals were broken so ordered a new one and everything has worked fine since.
I think you can lay to rest any fears regarding flammability of the paper label. The design serves to indicate the capacity of a fuse otherwise identical in size to fuses that range from 5A to 50A and reflects the simple production methods used by Lucas starting in 1902. Still in use today as an alternative to engraving or stamping the metal fuse caps, although the modern blue labels are boring and harder to read. Sure do miss those original graphics…
The paper label is unaffected by the normal operating temperature of a circuit, and only a short to ground will cause the fuse wire to heat up and break long before it gets an opportunity to glow and ignite the label. If the rating is correct for the circuit, warm fuses are more likely the result of dirty or corroded contacts generating resistance rather than a fault with the fuse itself.
My understanding of period Lucas/British vs American fuses is this:
-Lucas (British) fuses are of the Slow Blow variety. They withstand up to the rated Amps for a certain period of time without blowing and then blow. Allowing for a somewhat limited time period at a high load.Their actual full time load carrying level is about 1/2 the specified rating. So a 35 amp Lucas fuse as Jag and other British cars of the period used has a full time load rating of about 17.5amps and will allow for an overload of the circuit for a certain duration.
-Typical American fuses like a Buss or LIttlefuse amp rating is of the Fast Blow type and blows very quickly after reaching it’s rating. So a 35 amp fuse blows at 35amps. and runs continuously under that.
If you use a 35amp American fuse in an application where a 35amp Lucas fuse is spec’d you have a fuse that can allow the circuit to be continuously overloaded and will not be protecting the circuit at the design amps. Read melted wires and fire hazard. So if using American fuses in place of the Lucas fuses with the paper labels use ratings of about half for safe operation.
I had a similar thing with the floor mounted dimmer switch on my '75 Chevrolet. Low beams would occasional blink off and on. I pulled the connector off the switch and I could clearly see a bluish color on one of the blades like it had been hot. A new dimmer switch fixed things.
There is a lot of confusion surrounding fuse ratings, and one problem is that people think that they blow at a certain current. The truth is that, since they are low-tech physical devices, they are not very precise. According to Littelfuse, their 35A fuse has the following ratings for “Current” versus “Time before blowing” :
% of Ampere
Rating___________ Opening Time
100%____________4 hours, Minimum
135% ___________ 1 hour, Maximum
200%____________20 sec., Maximum
This means that a 35A fuse will handle 35A for a minimum of 4 hours. If you put 70A through it the fuse could last a full 20 seconds before it blows. That’s why I say that fuses in cars are designed to protect the wiring in case of a catastrophic short-circuit and not respond to slight overloads.