Hexonxonx · Sunday at 19:10

Good day,

Working to get my new-to-me 1970 Series IIa military ambulance safetied, and am having difficulties troubleshooting a non-flashing RH rear flasher. This is a negative earth vehicle.

What I've checked:

- The other 3 flashers work
- All bulbs work and are the exact same bulb, and I've swapped all 4 flasher bulbs in all sockets to confirm
- All sockets work, and I've replaced the RH rear socket
- 2-wire flasher module is new and works
- Checked the ground connection at rear chassis, and these are fine. There is continuity between the socket and ground connection
- Though the PO has replaced some wires at the bulkhead, they look correct in comparison with wiring diagrams

The problem socket is getting power - I can "see" it flashing on multimeter, and the voltage is the same across all sockets. But when I put a bulb in the socket, it does not light up. The only thing I can think of is that the bulb is drawing down current in some odd way that is preventing it from turning on, but not affecting the RH front flasher.

Any ideas?

Shedload · Sunday at 19:32

Long shot but do you have tow bar electrics fitted ?
I had similar issue with my Series 2. I thought I traced it to a poor bullet connection in the loom, just before it entered the chassis next to the gearbox. I reworked that connection and it worked for a while.
When it went again I disconnected all the wiring to the rear lights and refitted, minus tow bar which was not used.
Lo-and-behold, all indicators working as they should.

Bobsticle · Sunday at 20:07

Twang the spring in the holder and give the bulb a good twiddle.

Hexonxonx · Sunday at 20:20

Shedload said:
Long shot but do you have tow bar electrics fitted ?
I had similar issue with my Series 2. I thought I traced it to a poor bullet connection in the loom, just before it entered the chassis next to the gearbox. I reworked that connection and it worked for a while.
When it went again I disconnected all the wiring to the rear lights and refitted, minus tow bar which was not used.
Lo-and-behold, all indicators working as they should.

Thanks - no tow/trailer connections, though being a military vehicle it has a convoy light on a separate circuit.

Hexonxonx · Sunday at 20:41

Bobsticle said:
Twang the spring in the holder and give the bulb a good twiddle.

Oh, how I wish it were that easy...

Bobsticle · Sunday at 21:08

Hexonxonx said:
Oh, how I wish it were that easy...

Usually works for me. You can never know what the bulb to fitting connections are doing with a multimeter. Specially if it’s one of those crappy plastic aftermarket fittings. Might have the power at the terminals but it sounds like it’s not taking the leap of faith into the lamp.

Tall Ratbag · Sunday at 22:05

The problem is that voltmeters do not load the circuit like a bulb does. So, seeing your multimeter "flash" isn't the same, and isn't necessarily telling you anything.

The better approach is to look for voltage drops while the circuit is working. For example, put the positive probe of yourmultimeter on the metal body of the bulb, and the negative to a good earth on the chassis - if the bulb is well grounded, you will only see a very small voltage drop (0.2V or so), if the earth to the bulb is poor, you'll see a much larger voltage drop.

There are two big advantages to this approach - you don't break any connections to make the measurement,and youmeasure the circuit under load, i.e.,much closer to "real life".

Hexonxonx · Monday at 03:22

Tall Ratbag said:
...The better approach is to look for voltage drops while the circuit is working. For example, put the positive probe of yourmultimeter on the metal body of the bulb, and the negative to a good earth on the chassis - if the bulb is well grounded, you will only see a very small voltage drop (0.2V or so), if the earth to the bulb is poor, you'll see a much larger voltage drop.

Thanks - did as you suggested and the voltage is reading low (11.9v vs 13.4-14.2 on LH flasher). The tail lights, convoy light and license plate light all use a common ground connection on the rear frame and they all work fine, though I cleaned it for good measure.

Tomorrow I'll put my multimeter on the connections at the turn signal switch and the wiring connections at the bulkhead and see if I get the same readings.

Tall Ratbag · Monday at 17:23

>>(11.9v vs 13.4-14.2 on LH flasher)

This sounds like you didn't actually follow what I was saying. Look for voltage drops from a fully assembled circuit.

I'll give you another example

Imagine that you are checking the starter circuit, and you want to check the voltage drop between the battery and the chassis. You would not disconnect anything at all, but,would put your positive voltmeter probe to the negative battery terminal (assumine -ve earth), and the negative probe to a bright clean area of metal on the chassis. You would try the starter, and read the voltage drop at the same time. A high reading (anywhere above, say, 0.5 volts) indicates a bad earth connection. A perfect connection would have no voltage drop at all, and the voltmeter would read zero.

Hexonxonx · Tuesday at 11:45

Tall - I haven't tried your approach yet, however I was able to get it sorted.

As the issue seemed to be affecting only the one flasher, I focussed on tracing the green/white wire and found it frayed at the splice with the front flasher. Re-did the connection and now all is well.

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