TR2/3/3A Blowing a Fuse

[ckeithjordan]

My A3-A4 fuse has blown. I noticed the other day that the fuel gauge suddenly stopped working, so I double-checked the ground and it still isn’t working. Then I discovered today that the heater, turn signal flasher (and indicator light) and wipers aren’t working either. Not a surprise as they all (including the fuel gauge) share the same (green wire) circuit. I also found out that the OD is on the white wire side of the circuit, but I haven’t checked to see if it’s working. What’s the best way to narrow down the culprit, or is one of the above more likely than not to be the problem?

Thanks for your help.

 

[Geo Hahn]

One way to look into this without going through a box of fuses is to use an old headlamp in place of the fuse.

You connect one beam of the headlamp to each of the fuse holder (no fuse in place). Now when there is no draw the lamp is off. It may glow slightly when something is on. If it shines brightly that is a short.

With this in place try all the various things (mostly green wire stuff) that goes through that fuse and see if any one them cause the lamp to 'blow'.

Your OD should be unaffected as it and all white wire stuff (e.g. coil) is unfused.

 

[sp53]

I would try a new high fuse because the calibration was different in England then-- quoting Randall. Anyways, yes it all goes at once on the green wire, so you cannot pull one fuse at a times. Maybe unhook each device at a time should only be about 4 fuses until you know kinda and that is if your luck is bad. In addition, I would loosen the battery cables for the quick pull off. And yes--- sure---- look for the low hanging fruit. plus the wiper motor thing is interesting sometimes, some years the off removed the ground or something.
steve

 

[ckeithjordan]

Thanks for the suggestions. The fuse is a “correct” 35A one from TRF. I’m going to do the fault tracing as Geo suggests with a bulb. The wiring is all new from last year and has worked correctly up until now. I wonder which of the components (heater switch, trafficator, flasher, wiper motor/switch and fuel gauge [rebuilt last year]) would ”fail” and cause the problem.

 

[Graham H]

I have had indicator globes malfunction and cause a fault just something to keep in mind

Graham

 

[martx-5]

Here's a link to the wiring diagram that may help.

TR3 Wiring diagram

 

[bobhustead]

This may be a failed device or a short in the power wire on the way to the device. A good way to check this is to disconnect the power wire from all suspect devices, and install a fuse. If the fuse blows before any device is reconnected, you have a wiring short, not a device malfunction. If that happens, set a multimeter on ohms and connect the negative ground terminal (positive if positive ground) to engine or battery ground and probe each disconnected device power wire with the other ohm meter lead. The one that shows continuity is shorted. If more than one shows continuity, the problem is farther up the wire circuit (i.e., not the wire to one device). If the fuse does not blow, reconnect each device, one at a time, and the device that blows the fuse is the problem.

Bob

 

[sp53]

Keep us posted I want to hear more about the headlight method because I have never tried it. It sounds very cool for trouble shooting.

 

[Sarastro]

George has the best suggestion, in my opinion. Isolating the problem is just an exercise in logic--eliminate possibilities one by one until there is just one left. Like doing a Sudoku puzzle.

Start by removing all the green wires from the load (A4) side of the fuse. Then reconnect them one at a time until you see the light go on. Now, you have isolated the problem to one subsystem, and you can start disconnecting things powered by that wire until the light goes out. There's your problem!

It could be either a failed component or a short to the chassis somewhere--most likely at a connection. Lamp sockets are notorious for that kind of thing.

Keep in mind, fuses sometimes blow for no real reason, especially the kind that were used in mid-century cars. Age doesn't make them any more reliable. I suspect that's why safety-related parts of the electrical system, like the ignition, are not fused. So, perhaps the first step should be just to replace the fuse and see if the new one survives.

 

[ckeithjordan]

Thanks, Steve, one of the first things I did was replace the fuse with a like one (35A, from TRF) and it blew as soon as I turned on the ignition. I’m going to follow Geo’s fault tracing method, but it might be a day or two. Today is sewer replacement day and we had a death in the family yesterday, so my plate is full!

 

[Madflyer]

The light bulb is the only safe way to trace ground. Strip back to some copper and snap in with blown fuse. If all is bad lite will light check items at any point of acc. until lite goes out. lose battery cable or cut out switch good idea also. MF

 

[ckeithjordan]

OK, here are some test results. I used Geo's light bulb tracing method, which worked well. I used a blown fuse and soldered 24 inch long wires to each end, then soldered a single-filament 12V bulb to the wires. Thus, I was able to drop the fuse in the A3-A4 holder and place the bulb where I could easily see it glow or turn bright. The following items are fused through green wires to the A3-A4 "circuit":

Fan worked properly.
Fuel gauge worked properly (after I grounded it of course).
Stop lamp switch worked properly (the one on the RF inside fender).
Windshield wiper motor was OK when connected, but short (bright light) occurred when I turned on the wipers, by pulling the switch.
Trafficator usage (left turn/right turn) caused a short in both directions (bright light) and did not work.

So, any suggestions as to next step for additional fault tracing?

 

[bobhustead]

The trafficator wires in my original TR3 had the insulation chafed off at the place where they exit the tube at the bottom of the steering box. Check the turn signal wires for damage there.
Bob

 

[Sarastro]

The wipers might be OK. The motor looks like a low resistance when it isn't running, so that could turn on the light fairly brightly. I'd be more concerned with the turn signals. If the lamp comes on brightly when either direction is selected, it has to be something common to both, and there isn't much, since the R and L turn signal circuits are separate. So, that puts it either in the horn button/turn signal switch thingy, or someone disassembled both turn signals and put them together the same wrong way.

This is just ordinary logical reasoning, and that's really what all electrical troubleshooting consists of.

 

[ckeithjordan]

Update: I bench tested the DR2 wiper motor separately (with a 12V power supply) and it did not turn (also disconnected from the wipers), just hummed. I took off the end and the commutator slots appear caked with carbon and the brushes are worn down. I haven't put a multimeter to it to check resistance yet. I had previously cleaned and re-greased the wiper gear, but it looks a little gummy, so I will re-clean. I still need to pull the armature, inspect and clean it. It's original to the car, marked "6 57".

The turn signals still short when turned on in either direction. I'll start by replacing the flasher with another unit, in case it has failed.

 

[Graham H]

If your flasher unit is an original bimetal points type don't throw it away because the new electronic one may destroy itself after a very short time. I found the only thing the new ones were good for was using the shiny casing to house my original just to make it look new.

Graham

 

[ckeithjordan]

My "replacement" is a vintage one from 1957. The car has one from the mid-1980s when it was restored.

 

[sp53]

I had 2 electrical problems with a tr3 that were independent problems that happened about the same time, like days. The one problem was there are extra wires in the main harness of a tr3 for those side blinkers on European cars. The wires just sit there empty on a tr3 and mine filled with grease and oil and shorted out the fuse. The short was very difficult to find; finally a friend of mines dad found. He was an election at Boeing and fixed it fast. He reaches down and pulls up those old stock corner blinkers wires and said what this is? I think I said extra wires. The thing is they are not on any wiring diagram I have seen.. IF, shorted out they will blow the fuse. Plus I never thought to look at them because they are not part of the system on the car that is used here. I knew the wires were there from about 20 years earlier doing my blinkers, but forgot. The other problem was coincidental because it was the horn shorted. Stay with it Keith you got this.

Steve

 

[ckeithjordan]

Yeah, I'm slowly getting there. I've taken the wiper motor apart and have refurbished it, waiting on new brushes. If it checks out when reassembled (which it should), then I'm down to the turn signals. That one has me stumped. All of the wiring is new as of last year and everything was working before. Thanks.

 

[Graham H]

To find the problem with my indicators I had to take each globe out and try it until I found the one that had an internal short.

Graham