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MG MGB Technical - Starter Relay 72 MGB-GT

I noticed that on my starter relay there are 4 wires connected. According to the wiring diagram in Haynes,the brown should be on C1 terminal, the Black on W2, the white with red tracer on W1 and the white with brown tracer on C2.

For some reason the PO has both the white with red and the white with brown connected (piggy backed) to the W1 terminal.

Can anyone tell me what would be the most likely reason the PO would have done this. Would it have been that the relay went bad?

The car starts just fine hooked up this way. But I am wondering does this allow too much aperage to travel through my ingnition switch? I have owned the car for 5 years now a 1972 MGB-GT.

I have purchsed a new relay recently but before I hook up the wires the way they should be, just wanted to make sure I wasn't going to have a melt down in doing so.

So once again, why would the PO have hooked up both the WR and the WN to the the same W1 terminal? Let me know please what the possible reasons would be.

John Fraioli
Colorado USA
John Fraioli

don't always trust a Haynes (or most sources really)

have a look on Paul's excellent site -

and a link off Paul's site -

Nigel Atkins

Brown is power, black is earth, white/red is switch and white brown is solenoid.

W1 & W2 are the relay winding connectors and C1 C2 are the contact connectors.

By piggybacking the white/red and white/brown they have cut out the relay and driven the solenoid direct from the switch.

Nothing wrong with the Haynes/WM wiring diagrams.
Chris at Octarine Services

Chris, That is the conclusion I was thinking.
But why would someone do that? Bad Relay?
Would it be safe for me to install my new relay and hook the wires correctly. Just want to make sure nothing will/should go wrong. Also, I assmue the way it is hooked up now, would probably be bad on the ingnition switch after time no?
John F
John Fraioli

Probably a bad relay - wire it up correctly and see if it works!!

I can see no problem in wiring up your new one correctly - if it doesn't work then check there is actually power on the brown and the earth is good on the black.

It will be putting too much amperage though the ignition switch for long life wired as it is.
Chris at Octarine Services

Thanks Chris,
That is the kind of advice I was needing. I will try your suggestions and let the board know how I made out.
John Fraioli

OK, New starter relay installed. Wires hooked to terminals as indicated. Engine turns over and starts right up as it should. Did not even try wiring the old relay up correctly first. Since I had the new one just figured I would use it.

Before I discard the old relay is there anyway I can bench test it to see if is operational?

Thanks Chris for the help you have given me so far.

John F
John Fraioli

I agree that is was probably intentional to bypass a suspect relay.

Put 12v across W1 and W2 and an ohmmeter across C1 and C2, should switch between zero ohms and infinity as you apply and disconnect the 12v. However an Ohmmeter may not show problems with the contact as by their very nature poor connections are likely to be variable with the current they are passing. So if you are looking for an intermittent or bad connection it's always best to use the device i.e. switch or relay in the circuit is supposed to drive and measure the volt-drop across the contacts, that gives a much better indication of whether there are problems or not.
Paul Hunt

This thread was discussed between 29/06/2013 and 01/07/2013

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