MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Ignition Defeat?

I'm working on a US model 1978 MGB. The car has recently developed a starting problem. When I turn the key, all the electrics come on, including the ignition light, however, the starter does not engage.

When I hot-wire the terminals on the starter/solenoid, it engages and the car starts and runs properly. My question is, what's the best place to start hunting for a problem? I've looked at the wiring diagram and there does not seem to be and safety switches or fuses between the ignition and the solenoid. The diagram in the Hanynes manual does not seem to jive with my car fully though.

Any ideas?
Chris Connor

Take a look at the ignition switch. You'll need to take the steering column cowl off first to get to the switch. If you remove the switch from the lock mechanism (mind you don't lose the small set screw), the switch can be turned with a screwdriver to see if that replicates the problem. That tells you if the problem is a worn switch or if it is a mechanical problem with the tumbler. If the switch is worn and in need of replacing, you'd have to take it apart anyway. A new switch is available from any of the usual suspects (Moss, LBCarCo, Brit-tek, VB).
The other possibility is that it is the starter, but if it starts readily when jumpered, it is more likely the ignition switch. You can test this theory by removing the starter and taking it to your local auto parts store. Most of them can test the starter, and even tell you what the amperage draw is.
Hope this helps!
Paul K

Relay! Mounted on R/H inner wing at top near fuses. Black, cylindrical object. There should be two. One's the headlight main beam, the other's the starter circuit.
Tim Cuthill

Chris,

I agree with Tim, I had asimilar problem try tapping them gently to see if this makes them work, but replace them anyway. It solved all my problems (yes I replaced both). Mine was a 77 RB BGT.

Garreth
Garreth

I'll look for the relay. Does anyone have a description of the terminals on the relay?

I should be able to test this easily by jumpering it too - right? I can also check to see if it's getting voltage and eliminate the ignition switch (or identify it as the source of the problem).
Chris Connor

Could be the relay, and there are two, but the other is for the ignition not the headlamps. Also I think the black cylindrical one is for the ignition not the starter, which is the shiny rectangular one. In any case, the ignition relay has white, black, brown and white/brown wires, see below for the starter colours.

Normally when you turn the key to start there is a click as the relay operates, which is drowned out by a clonk from the solenoid, which is drowned out by the growl of the motor. If there is no click of the relay look for 12v on the white/red from the ignition switch to the relay and a ground on the black at the relay. If the relay clicks but no clonk check for 12v on the brown and brown/white at the relay and at the solenoid. I think the brown/white may have changed back to a white/red on late models, confusingly the same colour as from the ignition switch, but noticeably thicker.
Paul Hunt

Paul

Both relays started out cylindrical as standard, once they had changed from those big strange shaped metal units(76 model year from memory).The black cylinders have a habit of burning out the wires inside, but can be successfully resoldered with care - or replaced with any shape! comparable relay.

Dave
Dave Wellings

Crossed in the ether. The starter relay should have thin white/red on W1 and black on W2 but if these are reversed it doesn't matter. The brown should be on C1 and the bown/white or thick white/red on C2, but again it doesn't matter if these two are reversed. You need to check the voltages under load i.e. with the key turned to 'start'. You *could* jumper the thin white/red to the brown/white or thick white/red but that would try and pull much more current through the ignition switch than should be and may cause other damage. You should be able to jumper the thick white/red or brown/white to a brown and operate the starter if that part of the circuit is OK, indicating the problem is in the ignition switch, relay, or wire between them. Bear in mind that even if the relay clicks its contact may be bad.
Paul Hunt

I had the same problem. CHeck the wires at the starter. I had one of the wires work its way loose in the connector and it appeared as normal.

-mike
Mike Zaffarano

I think I've heard the click of a relay when I turn the key. Paul may be right, I hear the click of a relay, but not the clonk of the solenoid. I'll run through the wires noted above. I think that with this, I should be able to track down the problem, whether it is the ignition, relay, or wiring inbetween. Thanks!

Chris Connor

Chris - if you can hear the click of the relay the problem will be in the relay, solenoid or associated wiring, not the ignition switch or its wiring.
Paul Hunt

This thread was discussed between 09/12/2002 and 12/12/2002

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.