How to repair/replace the 2005, 2006, 2007, 2008, 2009 2010 Mustang Bad Hi and Low Speed Fan Relay.

 

If you have run into a problem with your mustang over heating the problem may be the POOR DESIGN that Ford did for the relay design that controls the cooling fan and its speeds.

Why did this happen: It happens because Ford thought they would save 3 cents and go with a relay and slip connector that is not rated for the amperage that the fan is pulling. Bad Ford!

You could get a new Fuse/Relay panel for under the hood, but my guess is this is going to happen again.

So here is my Fix – a Bosch that is actually rated for 30/40 amps with a connector that is ¼” not 1/16”.

What you will need:

(2) Bosch Relays (spend the extra 2$ and get the real deal.

(2) Relay Sockets (or in my case I got a dual Bosch Relay Socket)

Wire of at least 12 gauge & wire of at least 16 gauge

We are going to completely remove the shitty Ford Relays and replace them with a much better Bosch design, that is rated for more amperage and has a terminal that is much stouter.

 

 Take off the Relay/Fuse Cover, remove the 10mm Battery lead at the left of the fuse panel (NOTE: Cover this with electrical tape very well or better yet remove the battery leads), loosen the (4) 7mm bolts (these will not actually come out they are captive bolts), then lift up the Relay/Fuse socket board.  You will now have access to the 4 connector blocks underneath.  You only need the 2 on the left.

 Above, you see the two relay that we will be replacing mark HI and LO, they are marked 25 and 28 in the lid.

 

Here you can see them removed with the damage to the socket. This is thermal damage caused by the terminal that Ford chose to use not being rated for the amperage that needs to flow through the connector.  In the case of my car, the low speed did not suffer any damage, but we are just going to move both relays so that I don’t ever have to worry about this again.

 

 Another image of the damage to the terminal.

 

This image shows the damage to the Relay Socket Board. You can see from these shot that changing just one of the items: the Relay, the Relay/Fuse Socket Board, or the Wire connector would not have solved the problem as all three are damaged.  TOO many connections that are too small FORD. Poor design work!

 I created a 2 relay socket with 2 Bosch 30 amp relay in the sockets. The diagram goes like this:

 

 

In the above photo you can see the Relay Control Wires:

The thin Green with Violet Stripe is the Hi Speed control wire (85 on relay Hi Speed) Purple Arrow

The thin Dark Blue is the Lo Speed control wire (85 on relay Lo Speed) Purple Arrow

The 2 Red Wires in one socket are the other side of the relay control (86 on relays) Green Arrow

There is no need to cut these wires. Just tap on to them and tape up your work, see below photo:

 

 In this picture (above) you can see the relay output wire for the low and hi speed fan 87 on the relays. 

 Green with Yellow stripe is the low speed  [Green arrow]

Green with Violet is the high Speed   [Green arrow]

These will need to be cut and butt connected as the picture below shows:

 

With all those wires connected, you should only have the 12v+ Constant left, shown in the photo below (Green arrow) You will need to put a ring connector on this and connect it to the bolt that you removed in the beginning to disconnect the 12v battery source.

 When its all done, you can mount the relays to the shock tower upright like I did and it should all look like this:

 

 Cover in place, all done.