TR6 Tech Forum

Hi - I'm hoping some of the Triumph wiring experts on this forum might be able to provide some guidance on identifying the source of a wiring issue I’m having.

I purchased a restored 1972 TR6 last winter. The car had been through a complete restoration in 2018-2019 which included all new wiring.

The issue I’m having is that the output (downstream) side of the fuses for the purple and red circuits become very hot, too hot to keep your finger on the fuse when the headlights, parking lights, or the hazard warning switch is on. The input side of the fuses is warm, but not so hot that you can’t touch it. The heat transfers to the wires close to the fuse box but I couldn’t detect warm or hot areas further down the harness.

The fuse box is fairly new and the connectors all look clean and shiny, but they have become slightly discolored from the heat. Looking for possible points of corrosion and electrical resistance I removed the fuse box from its mounting position on the fender and everything was clean and corrosion-free underneath. I’ve also removed all the fuses and tightened the fuse box clips to make sure the connection to the fuses was solid and snug.

As a test I swapped the purple circuit and the brown input to the unused fuse box position to eliminate the fuse box position as the problem thinking that resistance was causing the heat but that had the same results. Output side of the fuse becomes very hot.

Based on reviewing numerous forum threads related to fuses and fuse boxes I’ve installed fuses per Dan Masters recommendations of 10A for the red circuit, 15A for the purple circuit, and 20A for the green circuit. Planning to purchase his book for guidance. I think I’m going to need it.

I’m stumped why the fuse for the purple circuit becomes so hot when it’s not directly related to the head lights or parking lights. But the fuse for the red circuit also gets hot to the touch with the lights on.

Another issue I noticed the other evening at dusk that may be related... while driving with the lights on the lamps for the dash gauges were all excessively dim except for the voltmeter which was installed by the PO to replace the original ammeter. All the gauges except the voltmeter appear to be original. The gauge lamp dimmer had minimal effect on brightness.

Can anyone provide any guidance how I might begin to narrow the source of this problem?

Thanks

Tom (TominMD)

In your fuse box picture...On the top fuse..on the right side of it there is blue wire with a red insulator plugged on that fuse along with the green circuit wires...Where is the other end of that blue wire ?

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ZS carb repairs
kencorsaw@aol.com

For starters you might try disconnecting 1 lead at a time to determine where all that current draw is going. Then go down stream from there to find what the issue is. ...J.D.

Tom,
Based just upon your photo, it doesn’t appear that the new wiring was with a stock harness. I would run an ohm meter between the output side and the various appliances on each circuit to guide you. You have some heavier than normal resistance somewhere in there. Check the connectors where the circuits branch. Are they soldered or crimped. You can start with those connectors at the fuse box and go thru each colored circuit.

Are you using the correct fuses?

"Install a US 35 Amp fuse into your LBC fuse box and the wiring harness will melt down before the fuse blows."

https://triumphtr6.info/Manuali/fuses.pdf



Edited 1 time(s). Last edit at 2024-06-20 06:18 AM by 46er.

Oh boy. Take all of the following with a grain of salt. I'm not even close to an automotive wiring expert.

The only thing I see as a common denominator is that the purple circuit powers both the flash to pass feature on the headlights and also the hazard switch.

As others said, try disconnecting the headlights, see if things get hot. Then disconnect the taillights. Then the flashers. Maybe that can get you in the right direction. Or maybe the purple wire first.

Also, I don't understand why or why the downstream side is hot, but the input side is not.

Finally, gauge lights are dim. I am not sure if the dimmer switch was replaced or if yours is 50 years old. Mine had two levels of brightness. OFF and DIM. Like others, I bypassed the dimmer and things got brighter. It has to be dark, not dusk to see my gauge lights.

Good luck.

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1972 Sapphire Blue TR6

1973 MGB Rover V8 LT 77

A picture is worth a thousand posts

It might have something to do with that Blue wire I asked about.
From the photo he posted it looks like a 'jumper'...It may not be but I can't tell from the picture..that's why I asked.
Maybe he's been unresponsive due to smoke and fire..you reckon ?

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ZS carb repairs
kencorsaw@aol.com

Hot wire may be of small section. or used. When I say used, I mean that if the copper inside is brown, it is because it is tired. the right color must be copper.

I saw that too, Ken. But I totally discounted it with a "nahhhhhh. No one would jumper like that." After thinking about it more, I have theories if so.

Let's see what he says.

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1972 Sapphire Blue TR6

1973 MGB Rover V8 LT 77

A picture is worth a thousand posts

Thanks for all of the comments. Lots of great information for me to digest and it puts me in a direction where I can start eliminating possibilities. I didn't know how to begin figuring this out.

I did some further investigation to try to answer the question about that dark blue wire that Ken questioned. That took a while and thankfully nothing has caught fire yet. I dissected (unwrapped) some of the wiring harness near the fuse box to try to determine where that blue wire goes. It disappears into the wrapped harness near the fuse box but doesn't show up about two feet further down the harness towards the front where I opened up the electrical tape wrap for inspection. Could be that the PO spliced it to a different color wire leading to the front but I don't see any lumps in the wrapped harness where a butt connector might have been used. I'll probably unwrap the entire run from fuse box to the grill/headlights area and replace the electrical tape wrap with wiring loom which has a nice tidy look and allows for easier inspection when needed.

As suggested in a couple responses, my next step will be to get to the connectors for the headlights and disconnect them and see if the fuses for the purple and red circuits still get too hot to touch with the lights switched on but disconnected. Then move on to the marker lights, and so on. I'm suspicious of the hazard flasher as mentioned by Aaron so I'll think about how I can eliminate that from suspicion.

Regarding Paul's comment about checking ohms from the fuse to various appliances, what should I be looking for in that test. I like using my voltage meter but I'm definitely a novice on the topic.

I've attached a couple more photos. The disconnected light blue wire seen dangling is for the courtesy light located near the ignition key. I disconnected it from the rear connector on the fuse box behind the purple wires because I suspected it early on in this issue, so its off the list of suspects.

Thanks!

Since there is only supposed to be GREEN wires protected by that top fuse, why don't you unplug that BLUE one and see if anything is affected...you can always plug it back if something stopped working.

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ZS carb repairs
kencorsaw@aol.com

All good suggestions about disconnecting different loads to trace the draw. Also mentioned was determining that you have the correct fuses. Dan Masters book covers the difference pretty well. Also make sure the clips that hold the fuse are good and tight. If you can spin the fuse easily they probably aren’t tight enough. They will get very hot and sometimes blow if there is not a good connection.

Resistance or loose connections is usually what cause electrical heat. More current is being supplied than can be safely handled.



Edited 1 time(s). Last edit at 2024-06-20 06:39 PM by 46er.

As far as using the ohm meter, I would first disconnect the battery. Then get a long lead with alligator clips on each end, attach one to the output side of the circuit you want to test at the fuse box and do some probing with the other end to the gauges/applications you find on the circuit. For example, at the green wire, off the fuse box, check things like wipers, heater. You have something that is causing high resistance in the circuits. Your wiring may not be as wonderful as the prior owner described.

If i were you i would get a stanley knife and cut that blue insulation off and inspect that crimp when someone tries to get two wires in a crimp that's designed for one wire always a bit dodgy. i would properly remove that crimp and replace with a crimp on each wire
then plug them in one at time and see if they still get warm. if someone cut strands out of the cables so they would fit in the crimp that would be the cause. and as previously stated if using fuses from the local auto store they must be lower amperage than stated on
the the fuse box lid.