It’s no secret that some of the electrics used on these cars are less than reliable (you’re probably thinking, wow, what a surprise). In particular, one item that I have always found to be even far below miserable is the original Jaguar starter relay. Many of you are probably familiar with this one- it is the rectangular shiny silver relay mounted on the firewall (XJ6 and XJ12) and on the rear right inner fenderwell (XJS). They’re just junk, and expensive as well. Additionally, unlike modern relays, if you wire the relay coil backwards (by mistake) you’ll burn out the unit. After several occasions where these relays died on me (at inopportune times, as well), I decided I needed a more reliable replacement. The starter relay itself doesn’t get much of a work out- it’s engaged perhaps 10-15 seconds max as the starter turns, then only again when the engine is restarted. Then I remembered those tidy little black plastic Bosch relays I’d used for fog lamp installations over the years. In all the years I ran them, not one failed. They’re rated at 20/30amps (the 2 different output contacts) which was more than enough to pull in a starter solenoid. So I gave it a try, and it has worked beautifully on each car. Since first trying this over 10 years ago, I have had zero failures. Also, these units come with a handy mounting tab on the case that just happens to easily fit on one of the original (old relay’s) mounting studs in the engine compartment- simple. Cost on these relays was something like $6 each when I first used them, and I’m seeing them now for around $3 on EBay- very affordable, especially compared to the original Jag piece at $75+.. What’s very interesting as well is that when the new XJ6 sedan (XJ40 model) was introduced in 1988, it was equipped with this sort of Bosch-based starter relay. Great minds think alike???

Anyway, here are the wiring details for this upgrade-the wiring colors are exactly what you should have on your current relay, so just transfer the wiring/connectors individually to the correct terminals on the new relay. Please let me know if you have any questions!!