Do Not Many People Know This, Or Is It Just Me?

[JohnD]

Had an ignition problem the other day, engine running, went to turn on fan - and everything stopped!

Complete ignition failure!

 

Now I have a relay in the ignition circuit, so that the manky little switches don't burn out, Happend to me once in a race, never again.

Went to look at the relay and it must have been overheating! Fuse on top warped and discolured. I whipped out the IR thermometer and it was a lot warmer than the O/drive relay next to it.

 

Luckily (taps nose) I had a spare!

Got it out and plugged that in, Turn on the ignition - and the smoke starts coming out of the wires to it!

Oh, grief.

 

Anyway shorten the story. Close examination of both relays showed me that they are NOT the same. Four terminals in same orientation so they plug into the same relay socket, 12V, 30A. BUT the terminals are NOT the same!

And some research finds that there are TWO types of standard relay, Type A and Type B.

See: http://www.vehicle-w...lays/relays.php and picture below.

 

For quick ID, the front post, the one edge on when the others are side on, may be either No.86 (the switching coil circuit)(Type A) or No.30 (the load circuit)(Type B ). In other words completely the opposite to each other!

 

And no wonder I nearly burnt out the car. Connect 12V along low resistance wiring directly to earth by using the wrong one and no wonder the smoke leaves in a hurry!

 

But worse. I go to Halfords to buy a new one, and they have a range, with and without fuse, 30A, 40A etc. But nothing about Type A or B, and I need a magnifying glass to read the tiny embossed numbers on the base of the relays. Luckily, I find one of the right type, and all is well.

 

But, am I the only person who doesn't know that four-post relays come in two distinct and dangerously different types?

If not, be warned!

 

JOhn

 

PS What WAS the problem? One of the female spade terminals in the socket had come loose. It was making intermittent contact! Which caused the overheat and the failure.

Edited July 26, 2013 by JohnD

[pomwah]

I for one did not know this. Someone should be "first up against the wall when the revolution comes" for allowing such a parlous state of affairs to exist.

 

Thanks for letting us know.

 

Cheers.

[esxefi]

yes,i found this out when upgrading my wiring and relays and now tippex what type it is on the top.

[PeteClan]

Had this problem several years ago with the relay provided with a Davis Craig water pump. Fortunately didn't suffer the same consequences as pump did not run so checked the terminals to find the difference. Always check now.

 

Pete Richards