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I have two glass fuses in a fuse box near to the control box on my  1958 TR3A. My workshop manual and some drawings from AUTO-WIRE show some different answers. I need to fit the correct fuse so that my cables are safe.

The two large brown cables are the horn supplies and have a new glass  fuse marked 35amp which I bought at a country fair at the weekend. it seems to be fine.

The other fuse is marked  20 Amps  and has been OK for at least two years  . I do not understand why there is no rating specified in the manual . 

Is 20 amps enough to protect the ignition etc.

Thanks Richard & Bruno

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The ignition circuit it's self should not be fused (also side / headlights) but the ignition switch powered auxilleries are ie wiper motor, heater motor, indicators, & brake lights.

20A sounds a bit low to me.


Edited by Lebro
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Hi Graham,

I have an Instruction Book, part No. 501528, Triumph Sports Car TR3, Fifth Edition – First Printing. Undated but the bottom half of the last page has been torn out so it might have contained a date?

The second page has a three-quarter side view of a TR3A so should be OK for your model.

Page 43 provides the following information :


The fuse carrier is located forward of the control box and houses two operating and two spare fuses.

The L.H. fuse (35 amp.) protects the horn, while the other fuse (35 amp.) protects those items which can only operate when the ignition is switched on, i.e., direction indicators, windscreen wipers, brake light, petrol gauge and heater (if fitted). A 25 amp. line fuse housed in a container is situated behind the centre instrument panel on U.S.A. vehicles. This fuse protects the side, tail and panel lights. When replacing a fuse, it is important to use the correct replacement ; the fuse value is marked on a coloured paper slip inside the tube.

A blown fuse will be indicated by the failure of all the units protected by it and is confirmed by examination of the fuse. If it is not possible to locate the cause of the trouble and new fuse blows immediately, the equipment should be examined by a Triumph or Lucas Agent or Service Depot.

If you are struggling to find correct value fuses I do have a selection of N.O.S. original Lucas fuses.

Regards, Richard

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