I put an extra fan on our 93 Cherokee some months back.

As standard, the Cherokee's had a mechanical fan and an electric. The electric came on with temp and with the AC.

I hate mechanical fans... power sucks.

So I did this trick with 2 electrics. I do want to lower the temp threshold, but that's a different subject.

Yesterday, bastet was getting it smogged, and it was running very hot. It ended up failing. Apparently, my fan wasn't working. Crap.

Last night I found out why... the cheap shit relay. I used a spare relay from a set of fog lights. It was a Bosch relay, figured that was pretty good... but it wasn't weather protected. I pull it apart, the connections are all corroded, I had no power from the battery and none from the signal wire.

In short, I rewired the entire thing using a surplus fan relay from a GM car of some sort I raided at the junk yard!

The lesson hear is simple... get used relays and their harness with pig tails, from your local u-pick-it lot.

Most places won't charge much at all, if anything, for these bits... but they are so much better than the garbage they give us.

When I was working, we (TYCO Electronics) bought some of Bosch's product line and most of Siemens to go along with our AMP line.
There are relays and then there are relays.
Our catalog of the smaller type of relays was over 2 inches thick.

The aftermarket is usually only interested in price. The automotive manufacturers are interested in quality, low failure rates (and price somewhat).

Just like the wire ring terminals you get at Pep Boys are junk, may work, may fail.