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TR4/4A In-Line fuse 25 or 35 Amp?

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bammons

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I may have missed it but I can't find where it specifies what amp the in-line fuse is for the horns (purple wire). I have 25 in there now but also came to realize my fuse box is supposed to have 35 (Lucas) (17-20amp Buss) whereas it had 25. So what is the proper fuse for the inline horn fuse holder? Bruce
 
The fuse should match the wire size. 10 gauge would take a 30 amp fuse.
Tom
 
If you look at the TR4 manual:


You see the horn fuse described as 35 amp.

TR4 horn fuse.png


This is where RGK's USA vs UK reference comes into play.

Edit: info on SFE fuses, mentioned in RGK's link: https://m.littelfuse.com/~/media/au.../glass-fuses/littelfuse_aftermarket_glass.pdf

Tom M.
 
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My non-expert point was that if you use the wire size (measure the core) you can match that with the British fuse size or the US fuse size, which as Ralph pointed out above, are quite different. The size designation will be different, and dangerous in this case if you use an American Buss 35 amp fuse rather than the British 35 amp fuse.
Tom
 
Ralph/Tom- As mentioned on my post, I am aware of the difference in Lucas and US ratings but I know some are not aware so it is good to mention it. I am not sure but I was thinking I had seen that the TR4 and TR4A had different ratings on the fuse box fuses, 25 Lucas vs 35 lucas (12 US vs 20 US). So that is what I am trying to determine is the TR4A rating desired not TR4 unless it is the same. I feel sure based on what I found the the fuse box on a TR4A uses 35 Lucas (20 US) fuses. But correct me if I am wrong. What the post is about though is the in-line horn fuses for a TR4A not a TR4 or anything else. I have the TR4A workshop manual but just have not seen the info. I am not going to cut into the wire to determine it's size so just looking for a authoritive answer from someone who knows. I will change to a 35 Lucas since that is shown in the TR4 info above. Bruce
 
- OK Ralph - That's the info I needed. Can you confirm that a TR4A does use a 35 Lucas (20 US) fuses in the fusebox? Since we are on the subject, and does the TR4 use different fuses ( just for educational purposes)? Bruce
 
bammons said:
Can you confirm that a TR4A does use a 35 Lucas (20 US) fuses in the fusebox? Since we are on the subject, and does the TR4 use different fuses
Click to expand...
The 4A and 4 have the same fuses indicated for the fuse box, check TRF for what they list. What do you mean by 'different'?
 
Ralph - If you look above at the picture Tom M provided of the shop manual for a TR4 it states that the fuse box fuses are 25 lucas. My understanding is that a TR4A uses 35 Lucas. I will do some more searching to verify that as I would like confirmation on this spec as well. Is so they are different and could make a difference. Tom I can verify that the Brown/Blue wire which is larger than some (goes Control Box/Starter/Light Switch) is 28 strand which makes it 14ga. I cannot verify any others but the purple wire with the in-line fuse is not as big. Bruce
 
I looked at my TR4A parts manual and found the answer to the fuses. It states TR4A use 35 lucas fuses in the fuse box not 25 amp shown above in the TR4 manual. So converting that to US spec that would be a 20amp Buss. Bruce Edit; Ralph we posted at the same time, but for anybody reading this the TR4 uses 25 not 35 lucas in the fuse box.
 
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I have measured LBC horn currents once or twice in the past; not TR4 horns, but ones that were similar. They always seemed to be around 10 amps each, so you will need at least a 20A fuse. I would make it 25, just to have a little margin.

The fuse specs in the owner's manual are for original wiring. You may not have that, and may not have original types of lights and horns and may have additional electrical stuff. The fuse ratings may have to be changed accordingly.

Wiring sizes for your home specify #10 wire for 30 amp circuits, #12 for 20 amp. But those are very conservative, for obvious reasons. Once, as a test, I put 10 amps through a foot of #20 wire, and while it got a little warm, it was in no danger of melting its insulation. I think that's why auto wiring generally has smaller conductors for a give circuit; it just doesn't have to be so conservative. You won't start a fire by putting 20 amps through a piece of #16 wire.
 
Ralph - You are showing 35amp for both TR4A and TR4 but what is posted above says different so I don't know why it is showing different things for the TR4. I have my answer for the TR4A but confusing for TR4 owners. Bruce
 
The first url in my post is incorrect, not sure why it brings up a thread instead of the parts manual, and there is no way to edit it. This is the correct parts manual for the 4 below. Both part manuals show the same part # and fuse size as 35.

app.box.com

TR4_Spare_Parts_Catalog.pdf | Powered by Box

TR4_Spare_Parts_Catalog
app.box.com app.box.com
 
Remember, British fuses are rated differently than American fuses. To my knowledge, the WSMs use British fuse ratings. PJ
 

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