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MGB 1977 MGB starter activates when key on the "on" position.


Freshman Member
A little background. Replaced the complete wiring harness due to PO creative wiring. No back up lamp, running lights, bad connectors,grounds etc. Started fine. Once the harness was replaced all the previous problems cleared up.

Since the re-wire the starter engages when the key is on the "on" position. The ignition switch has been replaced as well as the starter and ignition relays. The handbrake is unplugged from the harness and the car came without the EGR service counter.

The red and white wires that snap onto the starter relay are hot with the key on the "on' position. I have gone over the placement of the wires in the starter relay several times.

I am wondering in anybody has an insight as to what is feeding current to the red/white wires when they should be cold at that point of the key cycle.

Any help is appreciated!


Great Pumpkin
Country flag
Almost HAS to be the iggy switch. Either connected improperly or the switch is "FUBAR out of the box" (not unheard of).

A V.O. meter and some testing is in order.


Freshman Member
I keep wanting to blame the ignition switch as well. I picked up another thinking(hoping) it was a faulty replacement. Same story with the next one.


+1 for the wire connections to the switch or the switch itself.

Remove the white/red from the switch. Use a volt meter between chassis ground and each switch terminal while you hold the key turned all the way to the start position. You are looking for a terminal that is hot when the key is held in the start position and goes cold when you release the key. Put the white/red wire on that terminal.


Country flag
I had the same problem with my TR-6. Starter would energize with the key in the “ON” position.
A new ignition switch fixed it.


Staff member
Country flag
I am going to suggest that it may have to do with the anti smog circuits - which you may have inadvertantly reconnected with the new harness. With Ms. Triss (Midget not B) my starter would not stop running when I started the car. There are a couple of diodes - in my case - behind the glove box that I removed, though TBH what finally - bizarrely solved it was disconnecting the dual brake circuit pressure switch.

Take a look at this: https://www.mgexp.com/article/mgb/ignition-run-on.pdf


Freshman Member
Thanks for everyone's help. It ended up being that darn handbrake diode. Problem fixed and moving on to more enjoyable aspects of the project.
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