TR2/3/3A Fuses

Can someone give me the proper size (American) fuses in the fuse box and under the dash. In the fuse box I have a 35amp (paper inside) that is fine. The other fuse is 15 amp (no paper) and is blown. Everything on that circuit, obviously is not working. I have a TR3A. Thanks.

frankfast said:

Can someone give me the proper size (American) fuses in the fuse box and under the dash. In the fuse box I have a 35amp (paper inside) that is fine. The other fuse is 15 amp (no paper) and is blown. Everything on that circuit, obviously is not working. I have a TR3A. Thanks.

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This should help, written by Randall.


https://tr6.danielsonfamily.org/ForumImages/FuseComparison.pdf

Cheers
Tush

I understand that the ratings for the British and American fuses are different, but nowhere can I find the proper rating that should be used in the fuse box, British or American.

On earlier cars, the main fuse was 35 amps (Lucas rating system), while the horn fuse was 50 amps (again Lucas system). Later on, the horn fuse became 35 as well. I'm not sure of the change point offhand, but an AGC 20 seems to work fine with my horns.

AGC 20 would also be a suitable substitute for the Lucas 35. However, IMO, if you blew an AGC 15, chances are that you do have a short rather than just overloading the fuse.

The in-line fuse under the dash (only found on later cars) is supposed to be Lucas 25. AGC 15 works for me.

The Lucas ratings can be found in 'Practical Hints for the Maintenance of the Triumph TR3', which is effectively the owner's manual. Good thing for all TR3 owners to have, as it has many updates and changes from the workshop manual (like the fuse ratings). Printed reproductions are available from the usual suspects; or you can download a PDF from
https://drive.google.com/open?id=0B2H2NJt34OffNjQ4MTkyNjItZTVmYi00M2U2LWJhYWUtMjEyZDgxMzUyNzUw
(That is the 6th edition, suitable I believe for cars after TS60000. Sorry, I don't have the earlier editions scanned yet.)

I have a fuse box on the firewall with two fuses. There is a 35 amp that works the horn and is probably also the main fuse. The second fuse is a 15 amp that works the brake lights, directionals, gas gauge and wipers. That is the one that blew. I replaced it with a 15 amp AGC and everything now seems to be working. I can't see a fuse behind the dash amongst all the wiring. This car has a completely new harness so I don't even know if it exists. The schematic I have doesn't show it. Thanks for the help.

frankfast said:

I have a fuse box on the firewall with two fuses. There is a 35 amp that works the horn and is probably also the main fuse. The second fuse is a 15 amp that works the brake lights, directionals, gas gauge and wipers. That is the one that blew. I replaced it with a 15 amp AGC and everything now seems to be working. I can't see a fuse behind the dash amongst all the wiring. This car has a completely new harness so I don't even know if it exists. The schematic I have doesn't show it. Thanks for the help.

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The fuse that controls the brake lights, turn signals, wiper motor, and fuel gauge is what I called the main fuse. Probably not a good term for it, as it doesn't feed the other fuses or anything like that.
You can find an updated schematic, with the in-line fuse shown, in the Practical Hints I linked to above.

There are 6 different editions of PH (if you count the early ones which had the same part number but a different title); every one has a slightly different schematic and even that doesn't cover all the variations. The 4th edition was the first to show the in-line fuse (which is normally clipped to the inside of the dash, right above the shift lever). Here's a copy of the 4th edition schematic, which I modified to show the LHD connections for the control head.

(Click the thumbnail for a larger version, then click the magnifying glass for full size.)

PS, not in place unfortunately, but you can see the original metal in-line fuse holder from TS39781LO in the upper left corner of this photo.


The plastic one near the middle top is one I added, for the overdrive.

FWIW, the in-line fuse was added around TS38177, for US-spec cars only. So if your car is earlier, or was not originally a US-spec car, it wouldn't have had the in-line fuse originally.

But in my experience, it's fairly easy for the tail lamps to short internally. Without the in-line fuse, that usually ruins the headlight switch, causing you to have no headlights as well. So IMO the fuse is a worthy addition to earlier cars as well.

Could that fuse be added on the feed to the tail lights in the boot? If so, what wire would be best to fuse? 15 amp in-line fuse OK? Or, is there a good reason for placing the fuse in the gauge cluster location?

Cheers, Mike

Sure, it can be added. The factory chose to have it also protect the wiring to the panel and parking lights (everything controlled by that leg of the headlight switch), and while I've never had a short in those areas, I think there is still something to be said for that. They used the panel light switch as a tie point to join the wires to the tail, dash and parking lights, which is both convenient and means no changes to the wiring harness are needed. So that's the way I plan to go, when I get around to adding it to TS13571L.

But it's up to you if you want to locate the fuse somewhere else. You can run longer wires and still connect to the harness behind the instrument panel, or cut into the harness and splice into the red wire more or less anywhere you would like.

I'll put mine behind the panel, but probably use a plastic fuse holder and just let it hang on the wires. My previous TR3A had one of those AMCO oversize shift knobs, and I had a tendency to rub the edge of the dash when I shifted to 3rd gear. Never noticed it hurting my hand, but rubbing on that metal clip eventually scratched the finish on my driving gloves.

From your postings, it sounds like you don't have a shop manual. I think it would be a very good idea to get one--it will answer a lot of your questions, and give you the resources necessary to troubleshoot the problems you encounter.

As for the fuses, as long as the electrical system is unmodified, take the shop-manual values and divide by two. If it's modified, you have to figure out the loads and go from there. For more than you ever wanted to know about fusing, see https://www.nonlintec.com/sprite/electrical/.

Problem is, the TR3 factory workshop manual only has the wiring diagram and electrical information for a TR2. Early TR3 is the same, but there were enough changes along the way (like the change in fuse ratings, the addition of the in-line fuse, separate turn signals in the rear, self-parking wipers, rheostat for the dash lights, different starter, different generator, etc) that the information in the workshop manual is often confusing when working on a TR3A.

That's why I suggest starting with the "Practical Hints" manual instead, as it was updated with the later information. It also has other changes not found in the workshop manual, like the gearbox filler being on the side, only accessible from under the car; instead of being on the top accessible from inside the car.

But the workshop manual is a good thing to have too. You can download a PDF from https://drive.google.com/open?id=0B2H2NJt34OffYWZiN2VlZGMtNTkxMi00NGUzLWE4NzMtMGRkODRkYzU3MDU1
(to which I've tried to add some notes about later cars, manual errors and so on). Or there are paper reprints (mostly the 'Bentley manual') available from the usual suspects.