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MG MGB Technical - Removed alarm - not starting now

I'm just now getting my 74 B back into shape after a 10 year break for college, starting a family and my career. Glad to see that the forum is still going strong.

Today's project was to remove the faulty alarm system that I installed back in high school. I removed the brain and starter kill relay and thought that I had reconnected all of the original wires, but now the starter won't turn over at all.

When I turn the key I hear the fuel pump clicking for a second, but that's it. I recently bought a new battery and have it on the charger, so the ignition light is bright and the headlights don't dim when I turn the key.

Any ideas for troubleshooting this problem? I am still a novice mechanic.

Jeff
jeff74mg

Go here: http://www.advanceautowire.com/ and click on Stock Schematics on the left hand side and download the MGB one. That will help you be able to trace the problem. I would start tracing from the starter motor back and see where you don't have voltage when you should. As you trace back also pay attention to the connectors and state of the wires to look for problems there.

Simon
Simon Jansen

After looking at the wiring diagram, check the starter relay. The starter relay is easy to get to and it will help in determining if the problem is somewhere between the ignition switch and the relay or between the relay and the starter.
Does your car have the seatbelt interlock system?
Kimberly

If you can't even hear the starter relay clicking (should be possible with the bonnet up and the windows open even in an LHD) then the chances are you haven't reconnected the immobiliser wires correctly, if that is whay tou immobilised. OTOH maybe when you were removing the alarm you disturbed something else close by.

The ignition key puts out 12v on the white/red to one side of the relay winding, which should have a black earth/ground wire on the other side of the winding. One side of the contact should have a brown 12v feed and the other side of the contact a white/brown which goes to the solenoid.

If you have the sequential seat-belt system the white/red from the ignition switch goes to the control box and a yellow/pink comes from there to the starter relay.
Paul Hunt

Thanks for the suggestions so far. I just tested the ignition wire (white/red) and it is getting 12 volts on crank at the harness under the dash. I also ran a jumper wire between the brown and brown/white wires on the starter relay and it turned over the starter.

Does this indicate that my issue is somewhere between the sequential seatbelt module and the starter relay?

Haynes manual says that the sequential seatbelt module is behind the center console, but I can't see it even with the radio pulled. Is there a trick to getting at it?

Jeff
Jeff Pfeiffer

As you already found, there is probably still a disconnect between the ignition switch and starter relay.

Try jumping a wire from your ignition 12V when key is turned to START to your starter relay, to find if it triggers. This will confirm you have enough amperage to trigger the relay.

At this point, rather than figure out where the disconnect is, you could simply run a new wire.
Jeff Grant

Jeff, thanks I'll run a new wire to the starter relay and see if that fixes the problem.
Jeff Pfeiffer

Glad to help. That's the obvious disconnect since you confirmed 12V at the ignition and you confirmed the relay works by manually jumping it.
Jeff Grant

Just link the brown on the starter relay to the white/red or yellow/pink terminal on the relay. If that cranks the engine the relay and the wiring from there to the solenoid is OK. If you have a white/red at the relay then it is a break in that wire between there and the ignition switch. If you have a yellow/pink then anything in the sequential seat-belt system could be at fault, at its simplest you could just run a wire from the white/red at the ignition switch and connect it to the starter relay in place of the yellow/pink and bypass the seat-belt system altogether.
Paul Hunt

So I ended up running a new ignition wire from the switch to the starter relay, bypassing the seatbelt module. It worked great and after fixing a fuel leak I was out for a drive this afternoon.

Thanks to everyone for your help! I feel like I know my ignition electrical system much better now.

Jeff

Jeff Pfeiffer

This thread was discussed between 10/09/2008 and 11/09/2008

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