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MG MGA - Sorry, more blinker questions

Here's the outline.

The blinker wasn't working. Bought two more just in case.

Put in first blinker. Didn't work. Took it off and fussed with connections.

Then right front blinker would work, right rear wouldn't.

Left rear would work, right front wouldn't

Jewel wouldn't

Put in second. Same result except jewel worked. Then blinker 2 died.

I put in blinker one again. Same result as earlier, but jewel now works.

I checked all the bulbs and they are fine.

Any thoughts?
Tysen McCarthy

1500 or 1600? The circuits are different, so debugging process is different. Diagrams are here:

Grab a jumper wire and apply power to the four corner lamps first. For the 1500 that would be relay terminals 2, 3, 6, 7. For the 1600 that would be T/S switch terminals "R" for left and "L" for right (yes, really).

If some lamps don't light up, grab a test light and check for power at the lamp socket, jiggle the bulbs, and verify continuity of the snap connectors (and ground connections for the lamps). All four lamps must work before you worry about the flasher unit.

For the 1500, switch on, then jumper power to relay terminals 4 and 8 to verify that relay will click, in which case two lamps on same side (front and rear) should light up. If you only get one lamp, then you have a bad contact in the relay.

When you get two lamps to light up, front and rear one side, if it doesn't flash then probably a faulty flasher unit. The original style flasher only works with the electrical load of exactly two 21-watt lamps.

If the lamp wires are connected wrong, or the front lamp socket contact plate is rotated 180 degrees out of place, then you may get the low 6-watt filament to light, and the T/S lamp will be dim (like a parking light). This also will not flash when the load is not large enough to make the flasher cycle.

After covering all that in the specified order, let us know how you make out, and we may have to tackle issues of a faulty relay (1500).



Here's what I can tell you. Bear with me, I'm not great with electronics.

First its a 1600.

The flasher unit is clicking.

The right front is working and the left rear is working.

The flasher system has worked in the past. The only thing I've ever changed in the past is the flasher unit. The one I changed several years ago worked, until it didn't. I've tried two new ones, one didn't work. This one has got me to this point.

I tested continuity, without the ignition on, by putting one end of voltmeter to the inside center and the other end to the metal body of the unit. I got continuity in the blinker lights that don't work.

I also used the voltmeter to see if I have voltage at the blinker lights that don't work. I turned on the ignition, turned on the blinker switch and put one voltmeter lead at the center of socket and the other on the metal body of the unit. The voltage rose and fell with the clicking of the flasher unit.

I've tried replacement bulbs with no result.

Thanks as always.
Tysen McCarthy

So the flasher unit, and switch and two lamps are good, one in front and one in rear. The disconnect problems are in two different corner lamps.

When you have voltage "blinking: at the bulb socket, but the bulb itself does not light up, then
(a.) Burned out bulb
(b.) Bad connection bulb to socket (likely the ground side)
(c.) High resistance connection somewhere:
(c1.) snap connector in engine compartment
(c2.) snap connector immediately before lamp
(c3.) snap connector after lamp to ground
(c4.) ground connection on body

Install the bulb, then probe around to see where you get voltage. You should have voltage up to and including the bulb contact. If input voltage fails with bulb installed, then look farther up stream for the high resistance disconnect. If you have voltage on the ground side of the bulb socket, then look for disconnect in the ground circuit down stream.

Thanks as always Barney. As I mentioned, I really am not great at electrical systems so I'm going to ask several really basic questions.

1) Are there any photos or schematics of the assembly of the blinker light units so I know how to see where the various ground and hot wires connect internally?

2) What does high resistance connection mean? I'm assuming it means a less than perfect connection that is reducing the flow of electricity... Would using diaelectric grease help in those instances....particularly at the flasher unit?

3) When you say probe around with the bulb installed and look for voltage, I'm not entirely certain where to put the probes, can you give me a brief description?

Tysen McCarthy

More follow up. I pulled out the flasher body out of the car to start poking around. One question from the schematic. I'm not sure how its grounded. I can't tell from the schematic if its grounded directly to the body from the bolts or if there is a black wire.
Tysen McCarthy

Look here:

High resistance joint or contact is a loose or corroded connection. It will make a weak electrical contact that may be good enough to look like a connection, may even light up a low power test light. But when subject to high current load it will have large voltage drop and not pass enough current to light up a high power bulb.

Dielectric grease may prevent future corrosion, but the contact has to be cleaned for good connection before it will work.

Test light looks like this:

Ground the tail clip. When you touch a power source with the tip it will light up. No light, no power. You can also clip the tail to a power source, then use the probe to check for ground connections. Touching to ground makes light. No light, no ground.

This thread was discussed between 02/07/2017 and 08/07/2017

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