• Hi Guest!
    If you appreciate British Car Forum and our 25 years of supporting British car enthusiasts with technical and anicdotal information, collected from our thousands of great members, please support us with a low-cost subscription. You can become a supporting member for less than the dues of most car clubs.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Fuse Box Problems

Share this page

doates

doates

Senior Member
Offline
Hi everyone,

I have been trying to sort out my many electrical problems and have narrowed my lack of dash lights down to power is not coming out of the fuse box. When I turn the new headlight switch on I get power at the fuse but not out of it. The fuse is good (checked for continuity) and if I poke around on the output terminals enough it will show 12V but that disappears. I have cleaned the terminals (scraped with an xacto knife), changed fuses, etc.

I really don't want to change the fusebox, mainly because I don't want to take all the wiring off the firewall.

Is there anything to TRF's statement that "American fuses are not compatible with British electrical systems"? I am using standard glass fuses.

Any ideas?

Thanks Again
 
doates said:
Hi everyone,...Is there anything to TRF's statement that "American fuses are not compatible with British electrical systems"? I am using standard glass fuses.

Any ideas?

Thanks Again
Click to expand...

BINGO
You need to use 1/2 the value.
IIRC

But that is NOT your problem. My opinion
 
Can you post a picture of the fusebox, or a link to a photo? I'm not even sure what car you have ...

The American (AGC) fuses are very slightly longer, and slightly larger diameter (in addition to the rating difference that Don mentioned). For most of the British fuse boxes, that is not a problem. But I've heard that it is an issue with some of them.

When you say you get power at the fuse, but not out of it; are you checking right on the fuse end cap itself? If one is hot and the other not, then the fuse is bad even if it shows continuity.

Then check on the fuse clips. Again, if the power is there and not at the next point, you've found the bad spot, no matter how it tests when not under load.

If the fuse clip on the output side is still showing power (all these tests are with the lights on), then check at the fuse box terminal where the wire attaches (not on the wire terminal). And so on.

From what I can see on the Canley web site, a Mk IV Spit would have a fuse box somewhat similar in construction to my 71 Stags. They both had significant problems with the fuse box itself when I got them, and various devices that didn't work because the fuse box wasn't passing enough current. (Lots of fun, driving home in the rain with wipers that didn't wipe.) I was able to coax them back into operation, but the box had to come out to do it. I don't think there is any remedy with the box in place, other than bypassing it altogether.
 
Don't know about a Spit, but on a TR6, you can disassemble and really clean the fusebox. It made all the difference in the world for my car.
 
I am so excited.

For the 1st time in the year that my car has been back on the road....every light on the car works, correctly. Headlights, parking, turn signals, brake, reverse, dash, the key light and I even got a little buzz out of the door buzzer.

How am I supposed to use the main/dip beam? If I drive around with main beam on am I shining my brights in everyone's eye?

Now I can try to put the parcel shelves that built in and think about making my original radio function.

Thanks for your help
 
doates said:
How am I supposed to use the main/dip beam? If I drive around with main beam on am I shining my brights in everyone's eye?
Click to expand...
If we're talking later Spitfire with original switching and wiring, the stalk on the RH side of the column should be "upper position" for "main" (high) beam and "lower position" for "dipped" (low) beam. The stalk also should pull towards you for a "flash to pass" function.
 
"The stalk also should pull towards you for a "flash to pass" function."

Man, if that's not an optimistic feature on a Spit., I've never heard one.
 
Further to using American fuses in a British fusebox.I am going to install a Lucas SF4 fusebox in my TR3A. So if I have to use the American type then I would use 15 amp fuses instead of the 30 amps?
 
My suggestion would be to size the fuses to the devices you put on the new circuits. Add up the expected current draw for each fuse, add about 20%, then choose the next larger fuse.
(American fuses get derated at higher temperatures, like those potentially found under the hood, plus it's good to have some margin to cover start-up transients and so on)

Then make sure the wire is heavy enough to carry the fuse rated current. I frequently go a size larger (which is two AWG numbers smaller).

For example, if your load for the circuit totals 14 amps, adding 20% takes you over 15 amps, so a 20 amp fuse is appropriate. 14 AWG will safely carry 20 amps, so that will do (but 12 AWG would be better).
 
Back
Top