• Hi Guest! Being a Paying Supporter is NOT a requirement to participate at BCF. However, subscribing will help ensure we can continue to serve the LBC community for years to come. If you enjoy BCF and find our forum a useful resource...Please consider supporting us by **Upgrading**
    (PS: Subscribers don't see this banner)

Electricity question


Staff member
Country flag
Posting here instead of the Spridget board as the more input the better. I am confused. In the diagram below I have two wires and one dual female connector (Bullet connectors of course). (If you are interested, at the other end is the brake light switch - currently disconnected)

With the wires unplugged I get 12.10 V on one wire and 0 V on the other.

If I plug them in I get 6.06 V from the connector.

I can only presume this means that something is now connected in series but I just can't visualize it.

any thoughts? thanks all!



Jedi Trainee
Country flag
Yes, something must be in series. Also you must have some current flow to get a drop in voltage. Although the flow may be small.
Also, poor connections can be thought of as resistors. Add some current flow and the voltage will drop. I hope this helps. George


Freshman Member
Country flag
So what is happening from your description is that there is an electrical resistance in the path of both wires. So when they are connected together the two resistances act as a voltage divider giving the 6v reading. It may be that both sides have a really high resistance, you'll still see some voltage measurement with a modern meter.

From your description it sounds like the 12v wire has come from the fuse box and goes to the brake light switch with the bulbs the other side of the switch, is that right?

It that is the case I'd suggest using a bulb with croc clips to test whether the 12v wire can actually light the bulb. The trouble with voltmeter readings is that the high resistance of the voltmeter means that you are measuring the voltage with almost no load, which doesn't tell you if the connection is good enough to supply a useful current at the full voltage.


Staff member
Country flag
Thanks for this - Last night finally got it working. If I'm honest it may have been working - ish - all along. I took it all apart and checked each individual component all of which worked. I then took a closer look at the piece that went from the harness to the reverse switch and it was seriously degraded. Fortunately I have a big box O wires from the Vauxhall and the colours match (and the gauge is just a little thicker) so, made a new small harness and all works fine. I have never plugged in the brake failure warning light circuit as for some reason it causes the starter to run on. That was part of the circuit but, no longer. So hopefully today tape it all together and go for a run.
Similar threads
Thread starter Title Forum Replies Date
longbridgehealey Another I just don't understand electricity question Spridgets 6
Crankshaft TR2/3/3A Short on electricity, not short in. Triumph 6
jvandyke running out of electricity Spridgets 11
Bruce_B Distributor Electricity Queston to start engine Spridgets 5
G I don't trust nothing I can't see...electricity Triumph 4
Bob Claffie Electricity Austin Healey 17
nichola TR6 Question on new wiring harness Triumph 6
JPSmit Today's question - vacuum advance Spridgets 0
B Rotisserie question Spridgets 3
RJS TR4/4A TR4A Seat Upholstery - Piping Question Triumph 7
J TR6 73 TR6 Temp Gauge Wiring Question Triumph 6
71TR6 TR2/3/3A TR3A Scuttle Rim Question Triumph 4
JPSmit todays's job - and a question Spridgets 25
Y TR6 SU HS6 question Triumph 1
B TR6 TR6 1976 Clutch Choice Question Triumph 3
P '58 XK150 Dynalite Alternator swap question Jaguar 0
glemon TR2/3/3A Crankshaft Question Triumph 3
JPSmit Fuel line - gas tank question Restoration & Tools 5
Lin New Forum Upgrade Question Austin Healey 8
steveg TR6 Question - which bolt for heater return pipe bracket Triumph 3
jlaird MGB Strange daily question. MG 10
F TR2/3/3A Floor pan question Triumph 16
F TR2/3/3A Bumper bracket to frame question Triumph 7
Simmo General Tech Electrical question Triumph 4
T TR4/4A Surrey top question Triumph 18
JPSmit Vauxhall question - I know, weird eh?! Lotus 6
S TR2/3/3A C39/C40 question Triumph 7
nichola TR6 Seat belt reinforcing plate question Triumph 15
J TR6 TR6 Differential Rebuild question Triumph 6
D Tri carb: order of installation question. Austin Healey 5
C MGA Mirror question MG 0
JPSmit Todays question - wiring Spridgets 14
P TR6 1970 TR6 Timing Question Triumph 2
Lin Another Trafficator/Control Head Question Austin Healey 10
Lin Brake hard line question Austin Healey 4
J TR6 Vacuum Retard question Triumph 1
tahoe healey Dumb carb question Austin Healey 23
VooDooDaddy63 Basic E-Type Question: Fasteners - Metric or SAE or ...? Jaguar 15
J TR6 Moss HS6 SU conversion kit question Triumph 4
Lin "A" Pillars: A Question Austin Healey 8
D TR2/3/3A Overdrive question. Triumph 49
Lin Thermostat and blanking Sleeve question again Austin Healey 7
roscoe 5 speed conversion question Austin Healey 9
S TR6 Stromberg Bypass Valves - Question Triumph 11
JPSmit Suspension question Spridgets 1
roscoe Flywheel orientation question Austin Healey 3
steveg TR6 Moss advance kit maximum advance question Triumph 13
Lin Lucas coil question Austin Healey 8
ckeithjordan TR2/3/3A Wiring Harness Question[s] Triumph 10
C MGA Fuel gauge question MG 7

Similar threads