TR7 & TR8 Forum

I have a TR8 that has a build date of Aug1979 and it seems to have had the fuse box replaced. I just finished upgrading the brakes to the TWS 4 wheel disc setup, changed all of 5he fluids, did muffler delete, still have th3 rear resonators, put 15 inch wheels and tires. Just took it off my quick jack and now cleaning up the fuses. I pulled the fuses to see what was in there and found that they didn’t match the diagrams I got from this site. See attached, I am thinking that maybe some one just put in what they had ?

I also saw a Lucas fuse that says 25 amps continuous Lucas 50A is this a 25 or 50 amp fuse?

Can some one post a picture of the fuse positions on a 1979 TR8?

Jack

Unlike what you can buy in your local parts house, the Lucas fuses are designed to run continuously at about half of the stamped rating but will take a momentary spike (like when starting a fan motor when the draw is higher at start up) to the max rating on the fuse. What you will get with a fuse from your hardware store or parts house will run continuously at the stamped rating so one stamped with the same rating as the Lucas fuse may cause a melt down of your wiring. In addition the fuses from your parts house will be slightly longer and won't fit as they should in the fuse box. I have seen more that one of these fuse boxes that have been melted and ruined because someone stuck the wrong type of fuse in there.

I have no idea why the two different fuse labels (maybe fuel injected verse carbed? ) , but notice where you have written 50...that would be correct for the fuse below your writing for the battery horns/aux.



Edited 1 time(s). Last edit at 2025-06-02 07:44 PM by LaVerne.

Your Aug 1979 vehicle is likely a 1980 model year (what does the door plate say?), so don't start asking for 1979 fuse layout because there is a DIFFERENT and earlier fuse layout for the TR8 Coupes. They are "different" for sure, and I know because I own one. LaVerne has explained it well, and what you showed is a correct Lucas 50amp fuse, and the hand-written numbers you provided show that MOST of those numbers match what Triumph wants installed. Most vendors like Moss, TRF, TWS Motors, TS Imported and then the UK ones like Rimmer, S&S Prep and Robsport can provide the correct fuses for you.

The story on my car is that it was a pre-production DHC that was built and sent to a large California delearship as a demonstrator. The story is that a DHC was pulled and made into a TR8 to appease the dealer.The British trust certificate has the vin as TCN 160080-UFC built in January 1979 and was Carmine Red, the plate on the car says TCN 160080-UCF built Aug79 and Pageant blue . The trust certificate says the engine number is 12E-00524, the engine in the car is 12E-00741. Paul McDonald who keeps the list of TR8 coupes, is perplexed since my car has a battery box in the rear and the metal plate running on the passenger side covering the battery cables. It does not appear to be a converted TR7. I spoke with the gentleman at the Trust and he could not find my engine number is his documents and he said it could be a pre-production model since they didn’t keep good records on those builds. That is why I was asking about a 1979 TR8 fuse location.

Jack

Remember that all the fuse ratings on the fuse box label, in the repair manual, and on the fuses themselves are the DIN rating (German Industrial Rating - Deutsches Institut fur Normung) which specifies the BLOW current of the fuse. U.S. fuses use the UL rating (Underwriters Laboratories) that specifies the maximum continuous SAFE current.

The original fuses are METRIC 6mm x 25mm, while US fuses are Imperial 1/4" x 1". Thus US fuses are slightly larger, but with some determination can be forced into place in your fuse box. I do not recommend forcing them into place, as they can break - the original fuse box is sized such that you cannot easily substitute a US fuse for an original fuse.

Apparently enough silly Americans burned up their wiring using a UL rated fuse that the Brits felt obliged to include both ratings on their fuses. The lesser rating is the US equivalent, while the larger number is the DIN rating. If you are determined to use a fuse from your local auto parts store, you MUST double the UL rating number to match the DIN number. So a 25 amp Bussman fuse from Napa auto is equivalent to a 50 amp Lucas fuse - once again fitment may be a problem because of the slight difference in sizes.

Metric DIN fuses are available from Moss, British Wiring, Rimmers, etc.

Confusing? Yes, but only because the US and Germany use two different standards.

Vance

---

1980 Platinum Metallic TR8, frame off restoration, complete.
1974 Jensen Healey, now assembled and awaiting startup. =:-)



Edited 1 time(s). Last edit at 2025-06-03 09:22 PM by Darth V8R.

I just noticed that the labels would be the same if you turned one upside down with the exception of the 50 amp fuse verses the 35 amp fuse on the battery, aux, horn. Maybe for right and left hand drive?

Looking at my post picture I noticed that there is a number at the top and bottom of each fuse 1-2, 3-4……. And that the other diagram has the same numbering but switched to the bottom. The numbers seem to relate to the same fuse but just in a different position.IE 1-2 is the AC fan, 3-4 is the heated rear screen….. I have to get my guy who is good with wiring and see if we can determine what one fuse services and then we will know the proper sequence that my fuses are.

Jack
I believe that referees to the wire on each side of the fuse, some are different colour combos on each side of the fuse.
See diagrams enclosed
Also my glove box cover from my 1980 carb, if you want I can send the one from my 79 coupe,,,
Cheers
Tom

I wondered if you had missed the fuse ratings on the bottom row. My July 79 built TR8 coupe uses the upper chart shown in your photo, I copied one from the net and taped it to the inside of the fuse box cover as shown here.

You should be able to confirm the layout in your fuse box by just pulling the heater blower fuse and see if that kills the heater. You will need the key on for that test or you can pull any of those marked for the lights without the key on and see if it kills the matching light.

I now suspect that the lower chart in your photo maybe for right hand drive cars and the fuse box was just flipped 180 degrees. It still doesn't explain why the difference between a 35 amp fuse and a 50 amp fuse on the Battery, horns and Aux.

All that said I had enough issues with oxidation and poor contacts that I replaced my fuse box with ones that take modern spade fuses and use fuses rated at half the rating of the Lucas fuses.

I noticed in Tom’s schematics for the 1979 TR8 and the 1980 TR8 both have fuse contacts 1-2 in the same location, the lower left hand corner.

I am not sure what runs on the car. I know it started when I got it last November, and both headlights went up, but I am not sure what else works. There is no AC compressor or condenser and the. 2 hoses were cut leaving 5 inches in the engine bay. I was cleaning fuse panel first then looking at the bulbs in the lights then see what worked.

I have fuses from Moss, I will take out the buss ones and replace.

Thanks for listening.

Jack ( my grandfather was from Guelph)