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Hazard Lights

Moss Motors
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Shelby1115 Avatar
Shelby1115 Robert Kaylor
SHELBY, NC, USA   USA
Looking to get the hazard lights working on my '78 B. I know often times the issue is the switch which is where I started and have replaced it since when I pulled mine it was clearly bad since it feel apart. Even with the new switch still no luck. The flasher relay is also good as I switched it and the turn signal relay located under the passenger console. But still no luck. So what else should I start looking at to get them working. Fuses? Relays? Wiring? Any suggestions to try and locations of components is greatly appreciated?

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Rob-USLE Avatar
Rob-USLE Rob DE JOODE
Rotterdam, ZH, Netherlands   NLD
1977/1980 MGb have two relays one for the turning signals and one for the four hazard lights, both relays next to eachother behind/under the dashbox inside the car.
I recently has a broken hazard switch in my 80 US LE, bough a new one from a local dealer (ex Moss UK part) and gues what switch was broken, dealer ordered a new one and that one didn't work also,
awaiting switch number 3, so your new switch can be not correct.
If you disconnect the block from the hazard switch there are 6 wires, a group of 4 pinholes and 2 separepinholes , make a temporary connection between the separate two and at least you have a turning signal, if that relay is OK.

course2kid Jeffrey Johnson
Fountain Valley, CA, USA   USA
1979 MG MGB "Lucy (Lucifer)"
Here is a link to a great set of MGB schematics:

http://www.advanceautowire.com/mgb.pdf

IIRC, the schematic for a '78 should be on page 25.

What exactly are your hazard lights doing? Do they not light at all or do they just not blink? Do your turn signals work?

If your turn signals work, then you have power to the hazard light switch since the turn signal flasher gets power from the hazard switch. If the turn signals don't work, then check the 3rd fuse down in the fuse box (black plastic box on the passenger side fender well in the engine compartment). Note, that fuse is fed 12V on the white wire when the ignition switch is in the on position and provides 12v power to the hazard switch via the green wires. So, if your key is off, the hazards are not powered.

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Shelby1115 Avatar
Shelby1115 Robert Kaylor
SHELBY, NC, USA   USA
Turn signals work fine after replacing the broken switch. Hazard lights do nothing. Dont light or blink at all.

ClayJ Avatar
ClayJ Silver Member Clay Johnston
Mt. Olive, MS, USA   USA
1972 MG MGB
Your 78 should have a single multi-connector that the switch plugs to. As noted, poles 8 and 9 on one end of the switch are the turn-signal circuit.

Poles 1, 2, 3 and 4 are the hazard circuit group of four, these poles are all bridged when the switch is in "Hazard" mode, so the pole numbers to wire colors don't really matter, the four pole group should have LG/brown (supply), GW (left), GR(right) and LG/P (console light) wires connected.

The flasher cans should be well grounded.

The hazard flasher is powered by the always-on, unfused brown circuit. It supplies power to the switch on Light-green/brown stripe circuit to poles 1, 2, 3 or 4.

course2kid Jeffrey Johnson
Fountain Valley, CA, USA   USA
1979 MG MGB "Lucy (Lucifer)"
Check the following; push the hazard switch to the on position and see if the turn signals stop working. If they do, then pull the wiring harness connector off the hazard switch, rotate it 180 degrees, and put it back on. Now check turn signal operation with the hazards switched on and with them switched off. Most likely, the hazards and turn signals should both work now. If you may find that the hazards are on with the switch in the off position, you'll need to pull out the hazard switch, gently pry out the push button from the sides, flip it around, and pop it back in.

If the above doesn't work, you may have a bad switch. Pop it out and check the following. with the toggle tilted in toward the end with two pins, those two pins should have electrical continuity to provide power to the turn signal flasher. With the toggle tilted in on the four pin end, all four of those pins should have electrical continuity. In neither position will there be continuity between the group of two pibs and the group of four pins. If the switch doesn't meet these checks, return it for a replacement (or disassemble and fix it if so inclined).

pshipley Avatar
pshipley Silver Member Paul Shipley
Kelowna, BC, Canada   CAN
1980 MG MGB
I went through a similar issue earlier this fall. Lots of tips and diagrams in the thread here: http://www.mgexp.com/phorum/read.php?1,3601768 including when I figured out what the DPO had done.

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gofastandfalldown Avatar
gofastandfalldown Glen Horne
Edmonton, Alberta, Canada   CAN
1970 MG MGB MkII "Miss Pandora Moneypit"
Do the easy stuff first....

The hazards are fed from a different power source than the turn signals.

The hazards have an in-line fuse on the power feed. Check that first.

gofastandfalldown Avatar
gofastandfalldown Glen Horne
Edmonton, Alberta, Canada   CAN
1970 MG MGB MkII "Miss Pandora Moneypit"
In reply to # 3627445 by ClayJ
The hazard flasher is powered by the always-on, unfused brown circuit. It supplies power to the switch on Light-green/brown stripe circuit to poles 1, 2, 3 or 4.

The hazards are fed from a fused brown circuit. The fuse is shown on the schematic in the upper left corner.

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Nicecar Avatar
Nicecar Gary (ex "Harv") G
Victoria, BC, Canada   CAN
1980 MG MGB "Red On Red On Red"
Fuse is an in-line in Engine Bay.
The other in-line in bay is Anti-run-on.

Clay #5 should have said poles 7 & 8, not 8 and 9.

oleanderjoe Avatar
oleanderjoe Silver Member Joseph Baba
Fresno, Ca, USA   USA
Flasher cans don't need a ground. They work just hanging by the wires.

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