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TR2/3/3A What Might Cause The Entire Electrical System on my TR3A to Die?

Lbp

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I recently got my '58 TR3A back for the body shop where it spent 6 months getting body work and new paint. Yesterday, I took it to work. On the way home, I pulled the knob for the headlights and the car immediately died. No electrical anything. Nada. Both fuses look good. Suggestions? Ideas?

Bill
 

TR3driver

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I agree that is a good possibility, but I hate working under the dash. So I would start by checking for power on the connections near the control box. If you don't find power on terminal A1, then the problem is between there and the battery. (The wire on A1 is the wire that feeds the headlight switch, which as TFB said then feeds the ignition switch.)

BTW, the TR3/A/B has no fuses in the headlight or ignition circuits, unless someone has added them. One of the fuses in the block under the hood is only for the horns; the other is for wipers, heater, turn signals, brake lights and fuel gauge. There may be a third in-line fuse clipped inside the bottom edge of the dash; if so it only controls the dash and tail lights. On earlier cars, those lights are unfused as well.
 

Got_All_4

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This should sum it up!
 

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Geo Hahn

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I predict a loose connection behind the dash. Like Randall, the 'dashboard limbo' doesn't go well with my age (and girth I suppose) but those pre-Lucar connections (screw clamping done on a stripped wire) seem prone to loosening. You might try just reaching up there and fiddling with the wires and see if everything comes back to life. If so then you can decide whether to fix it or just fiddle every time the outage recurs.
 

sammyb

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Start with the easiest one -- check the battery connections...and if you have a quick disconnect knob, make sure it's tight. This was a common problem on my Ferrari 308 GT4. I would drive it, come back out to start it -- it would crank and then I'd turn the key again and the whole car would be totally dead from bumper to bumper. I'd turn the little green knob tight as possible and the car would spring back to life. I finally got rid of the knob.

Specific to the TR3 -- check both battery connections and the cable that goes to the body to ensure they are all tight.
 

sammyb

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The ammeter itself can also go POOF. That happened on my TR-250 back in 1998. Put a test meter on it (one on each lead) and see if current passes through. If it doesn't, you need a new ammeter. You can place all wires on one side of the ammeter to bypass it. That's what I did in my TR-250 until I got a replacement.
 
OP
Lbp

Lbp

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Thanks everyone for all this info. Weather permitting, I'll be out with my multimeter attempting to track down the problem this weekend.

Bill
 

RJS

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+3 on the ammeter. I had this exact problem several years ago. Was out for a nice drive and the instant I switched on the headlights the engine completely died.

Inspect your voltage drop (difference) from battery to your ignition coil (positive terminal). Ideal drop should be no more than 0.5v. If your getting more than a 1.0v drop it's probably in the ammeter since all the power runs through there. I was getting 12.45v at the battery and about 7.0v at the ignition coil. When I turned on the headlights there wasn't enough voltage left to the coil to generate any spark.

I removed the ammeter, replaced the male connectors with new and replaced the female connectors with new (Lucar 30amp). The improvement was huge in headlights, etc. at idle. I also think I get a much hotter spark now because the engine fires up instantly now when I crank it over. Everything functions at idle again: headlights, tail lights, horn, turn signals, fuel & temp gauges.

Bob
PS: that would have also explained the "steaming-up" of my ammeter before I solved this. The corroded connections were generating a lot of heat in the gauge itself ( which only serves to corrode them more...it's a vicious circle)
 
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Lbp

Lbp

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A true Homer "doooh" moment! After checking the ammeter (which seemed fine), I started tracing wires from the battery. Battery > A1? No problem. Across the fuse to A2? Nada? Pulled the fuse and discovered it was blown in a way that didn't appear obvious when I eyeballed it on the side of the road where it died. Being as the fuse was at least 32 years old, I guess I wasn't surprised. I ran down to the auto parts store and bought some new fuses. Slapped one in and everything came back to life! Doooh!

Bill
 

TR3driver

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You of course remembered to get a 20 amp fuse, instead of the 35 amp suggested by the books.

Also a good idea to shine up the clips on the fuse block, where they grab the fuse. I had a very similar problem years ago, and after the new fuse also let go within a few weeks, I realized that the clips had just enough corrosion on them to get hot. If they get hot enough long enough, the solder inside the fuse melts.
 
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Lbp

Lbp

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You of course remembered to get a 20 amp fuse, instead of the 35 amp suggested by the books.


I replaced the fuse with a 35 amp, just like the one that came out. I haven't heard about switching to 20 amp. Is that the general preference around here?
 

angelfj1

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I replaced the fuse with a 35 amp, just like the one that came out. I haven't heard about switching to 20 amp. Is that the general preference around here?


The British fuse standard lists fuses by the current at which they will blow. So, a 35 amp British fuse will blow just at 35 amps, with no appreciable time delay. The US standard, adopted by SAE, lists fuses by their continuous current rating. So a 35 amp SAE fuse will carry 35 amps continuously or until your wiring has melted and possibly caused a fire. This is why Randall suggested a 20 amo SAE fuse, which would blow before your load reached 35 amps. So, check the type of fuse you bought and reconsider your situation.
 

TR3driver

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The British fuse standard lists fuses by the current at which they will blow. So, a 35 amp British fuse will blow just at 35 amps, with no appreciable time delay. The US standard, adopted by SAE, lists fuses by their continuous current rating. So a 35 amp SAE fuse will carry 35 amps continuously or until your wiring has melted and possibly caused a fire. This is why Randall suggested a 20 amo SAE fuse, which would blow before your load reached 35 amps. So, check the type of fuse you bought and reconsider your situation.
Exactly!

The other alternative is to buy a proper Lucas fuse from an LBC supplier (Moss, TRF et al). Might even be a better choice, since the Lucas fuse is a very slightly different size than the SAE fuses.

The ISOA put on a very convincing demonstration at the 2005 VTR in Rockford, IL. They hooked up a car battery, fuse holder, length of harness wire and a dummy load consisting of a bunch of old headlight bulbs with switches to vary the load. For the demonstration, they started with a fresh piece of harness wire and a Lucas fuse, and increased the load until the fuse blew. Then they inserted a SAE fuse with the same rating, and turned up the load until the wire smoked and melted. The fuse was still good!
 

Andrew Mace

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It is, perhaps, worth noting that older Lucas 35 amp fuses were labeled simply as such, and behaved as described above. However, for the past...I don't know...30 years or so if not longer, those same Lucas fuses gained an additional "legend" saying not only 35 amps but 17 amps continuous. Hence the near-equivalent 20 amp "SAE" fuse.
 

TR3driver

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It is, perhaps, worth noting that older Lucas 35 amp fuses were labeled simply as such, and behaved as described above. However, for the past...I don't know...30 years or so if not longer, those same Lucas fuses gained an additional "legend" saying not only 35 amps but 17 amps continuous.
Indeed most if not all of the old Lucas fuses I have do have that legend inside the glass (except ISTR it says 17.5 amps). But the tricky part is that the books (eg Practical Hints) only give the 35 amp rating, and usually after the fuse blows, the piece of paper inside is illegible :smile:
 

sammyb

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The important thing is that it's a 25-cent fix. We like those!!! Sure as heck beats the big time and money (like, say, needing a new wiring harness) ones.
 
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