After test driving a Jag 4.2 S type version R S/C. I checked the electrical box in the trunk/boot. all of the yellow colored relays were pretty warm to the touch. Is this normal or is something overloading somewhere.
much appreciaite any help Mark

 

Welcome markstartmees ...I'm not familiar with the S type (but stay with basic car sense). We first, we need to get you into the correct forum (X200) so if there is a go to ..to check, they can help.
But it depends on what you call warm? If there is an issue, the battery should be somewhat warm (not hot) to the touch. If its hot, that's a bad grounding issue. The battery will suffer along with an issue elsewhere. I would really be looking at the battery cables, ...check for any (and I mean any) corrosion, especially down into the shielding. Any corrosion (especially on the negative) will cause a load draw which will create heat (need to replace any corroded cabling). If you don't see any corrosion, run or drive the car for a few minutes. After shut down, go to the trunk and touch the shielding on the battery cables, they should be air temp.

 

First, the car would be a 2002.5 model year or later and not 2002. This makes a difference in identifying part numbers and configuration.

It is not normal for any relay to be warm, ie much above ambient temp. This era of S-type suffered from water ingress in the trunk which led to serious electrical issues. Look for signs of water stains in the spare tire area.

 

It is perfectly normal for relays to heat up a little bit. The actuating coil (the electromagnet) consumes energy, some of which turns into heat.

Too much heat, on the other hand, indicates a problem. If the switch contacts are corroded, they will also consume energy and create heat, like a miniature arc welder. Here's a failed relay, showing evidence of arcing from bad contacts.




So how much heat is too much? Some heat (from the coil) is normal, but too much (arcing contacts) is bad. I checked the rear power distribution box on my '02 for comparison. This was after a 10 mile trip on a 75F day. The box itself and surrounding area measured about 90F, which I think was due to radiant heat from the nearby muffler.

The box has 8 relays. Seven of them measured about 125F. The oddball measured about 90F, same as ambient at the box. This was R3, for the rear window defroster, obviously not in use today and so not energized. I've had no electrical issues of late, and since all energized relays were about the same, I'd say 125F is perfectly fine.

I deal with similar relays all the time in my line of work. The only difference is they have sealed metal cases. It is normal for them to be warm. If we suspect a relay isn't energized, whether from an open coil or no command, we check if it feels cold. If we suspect the contacts aren't making a good connection, the case will be hot to the touch if bad.

 

Yes perfectly normal.
In my 2005 STR anyway.
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