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MG MGB Technical - Starter Relay Terminals

I am pretty sure my starter relay is shot based on what I've read in most of the archive articles on this issue. I bought a generic starter relay from a local auto parts dealer that has the same terminal layout as the Lucas unit but instead of the W, C, C1 etc, it only has numbers 1,2,3,4. I've seen other threads referring to numbers like 85, etc that cross reference back to the wire colour codes but haven't seen any that have simple numbering like the one I have.

Anyone used any relays like this? I am assuming that with the same terminal layout, it should be the same connections as the Lucas relay.

Thanks

Mike
Mike

Mike - Use a multimeter set to read ohms on the loswest scale. Check the terminals by clamping a lead to one termainal then touching the other lead to each of the other three terminals in turn until you find a pair of terminals that reads some resistance (I am not sure how much resistance you will read, but it will be greater than 0). Mark these two terminals as the coil. Check the other two terminals to insure that there is infinite resistance between them with no power applied to the coil of the relay - these two terminals are the cotacts of the relay. You can now hook the relay into the circuit. Cheers - Dave
David DuBois

Mike-

What store did you get the relay from? Do you have a part number? Brand name? Is there any kind of schematic supplied with the relay? Is a schematic embossed on the relay? Was there any literature explaining the terminals on the relay?
Kimberly

Most Japanese cars use relays marked 1,2,3 & 4. All I have seen use 3 & 4 for the coil and 1 & 2 are contacts. But as Dave said it's best to check.

W1= 3
W2= 4
C1= 1
C2= 2

Clifton
Clifton Gordon

My Toyota Celica manual shows the numbering as being different according to what the relay is used for, even when the relays are both the same i.e. a single normally open contact. However this may be when one relay is round and the other is square.

I'd do the test David advises. As long as you get the same resistance across the winding pair in both directions, it won't matter which way round these are connected to the white/red and black wires. Likewise for the contact pair it won't matter which way round the brown and white/brown go. But if the winding pair measures around 70 ohms in one direction and much lower than that in the other the relay has a diode across the winding and it will be important to get the white/red and black wires round the right way. This can be tricky. The safest way is to wire the relay winding terminals in series with a 12v headlamp bulb to a 12v supply. If the lamp is dim and the relay clicks that is the correct polarity, so note which terminal goes to the +ve and the white/red goes on that, and which goes to the -ve and the black goes on that. If the lamp comes on full brightness and the relay doesn't click, it needs to be reversed.

Also check that there is infinite resistance between each of the contact terminals and each of the winding terminals, some relays have internal connections.
Paul Hunt 2

Thanks Paul. I looked in my Tacoma truck manual and most of their relays are as noted above. I just looked at the wiring diagram for the Mazda Protege 5 and there are no relay pin numbers listed in the wiring diagrams.
I'm looking at a fan relay from an older Corolla. It's numbered 1,2,3 & 4. There is a diagram on the relay, 2 & 4 are contacts, 1 & 4 are coil. I cannot erase what I said above but it is correct for some applications and is not correct for some. Check before using.

Clifton
Clifton Gordon

I'm using NAPA AR623 that fits a Dodge truck and was only $12. The parts store happened to have the Dodge Haynes manual in their rack and they photocopied the page from the wiring schematic for me.
Terminal 87 (T40 and 12BR) goes to the starter and it's the same as C2 with the white/brown wire to the solenoid.
Terminal 30 (A2, 12PK and BK) is the brown power wire from the fuse block and is C1.
Terminal 85 (T41 and 22KB/WT) is the ground wire, black, and W2 on the original relay.
Terminal 86 (T141, 14YL and RD) is the wire from the ignition switch, W1 on the original. On MG's with the sequential seat belt module it's yellow/pink but on normal cars it's white/red.
This little relay works great except that there's no way to mount it to the inner fender. It's meant to be plugged into a fuse box. It lays on the bulkhead and seems to be fine so far.
Hope that helps.
Ken Thompson
1974 mgb roadster
Kenneth Thompson

This thread was discussed between 31/08/2007 and 01/09/2007

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