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MG MGB Technical - Oh Strange One Prince

Last night on the way home, the radio started on and off, then the indicators wouldn't flicker, then the lights dimmed. The 77 mgb roadster started backfiring and stalling. Shut the lights off and the car ran ok again. I could then see it was lack of juice, but received no alternator light during any of this. Made it home thankfully Oh Prince ( you big Creep) who never sleeps! So, I assume the bats gone, or the new high output alt is fried, or the starter relay or the voltage stabilizer. Am so curious why I never got a red alt light? Surely the bat must've been on discharge and the alt light should have been singing. This is the same car that runs on after the key is pulled. Sometimes I'm in the house before the engine switches off! Paul or anyone out there with thoughts and first strike advice? Thx, Vic
vem myers

Vic,
1) This is most likely a bad connection problem. DO NOT assume anything until you check the part in question. You should know this by now!
2) The 77 NA Bs have a known wiring problem that causes the "no-shut-down" thing. It's on Paul's site I think. He has discussed it a couple of times on here. I recently fixed one with his instructions.
3) Got oil pressure?
FRM
FR Millmore

Vic, (and anyone else with the no stop problem),
The easiest way to fix this is:
Remove tach.
Find the IGN indicator lamp.
Cut W from harness to lamp; give yourself a couple of inches wire on the lamp. Tape the harness end of the W so it can't touch anything.
Splice a distinctive (ideally a WN) wire to the W on the lamp.
Run this across the back of the dash and along harness to the IGN relay.
Connect to the WN terminal of relay or fusebox.
Refit tach.
Now it will shut off.
FRM
FR Millmore

Actually the easiest way is to locate the coil feed wire at the fusebox (white/brown) and move it from there to the white terminal of the relay, which it should reach anyway. For some reason the factory did *both* mods when either on their own should have cured it.

Vern, when you find it it will be obvious! If the alternator plug is loose you will not get a charge *or* an ignition warning light, and the gradually discharging battery can cause the symptoms you describe (BT, DT, I admit). The real symptom of that fault is no warning light when you first turn on the ignition, and how many of us check for that before cranking?
Paul Hunt 2

Check the Brown wire at the starter solenoid.

On some cars it is held on with a push-on tab
connector and it often loosens and falls away.

When this happens, your gauges drop dead
straight away, and the engine sputters and
conks out, no Alt light warning.
Daniel Wong

Paul,
Yep, that's easier! The car I did just happens to be here now. Can't fathom how this thing is wired. It has the usual 3W > WK (resistor wire) splice sticking out of the harness, so I figured that the coil was fed off this as it usually is. The WK becomes WLG by the time it gets to the coil. No sign of a WN > W or anything else. If there is a splice internal to the harness, it's the first one I've met on a British car. The coil IS fed off the relay WN, but if there is an obscure splice, it could be feeding other things too. I didn't have any desire to cut the harness open to find out!
FRM
FR Millmore

Daniel - you *should* get the alt light glowing in that event while the engine is still spinning. The alt is still generating while it us spinning and outputting 12v on the brown and the brown/yellow. The brown/yellow goes through the warning light to its white side, and because the 12v from the ignition switch is no longer present on the white to dim the warning light it can 'see' a ground through the coil, on cars without an ignition relay at least.
Paul Hunt 2

Vem,
I regards to your original running question....
Check your battery connections, and where the ground cable attaches to the car body. Also ckeck the engine ground strap and make sure all these connections are clean & rust free. Sounds like a bad ground or battery connection to me.
Good Luck,
Ralph
Ralph

Thanx guys. I'll let you know who wins the chase here! Vic
vem myers

This thread was discussed between 09/10/2005 and 16/10/2005

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