I need help on the relocation of the Opus amp on my 1971 V12 E-type.
Ever since done, the tach goes wild when reved above 4000 rpm.
Thanks
Chad Bolles

Submitted by NE52-32043 on Thu, 11/20/2003 - 15:16

Chad,

If you used the proper OPUS amp with longer lead, I don't understand why the tach would go crazy. When changing to other types of ignition systems, like the Crane, you often have to put a diode in the tach line to prevent this. But yours sounds okay up to 4000 rpm.

Did you check the tach lead from connector to tach? You might want to be sure that all the connections are good, including on the back of the tach, and that you have a good ground on the tach itself. Remove all of the connectors and clean them up really well. Also, check the wires in the connectors for corrosion. And make sure that the lead for the tach pickup in the connector didn't get pushed out of the other side when you inserted the connector into the block. Beyond that, I'm at a loss.

Steve Weinstein
'72 E-type 2+2
'70 XKE FHC

Submitted by NE52-32043 on Mon, 11/17/2003 - 10:27

Chad,

How did you do it and where did you relocate it to? If you spliced wire into the harness to lengthen it, you've got a problem. The wiring harness on the OPUS unit was part of the tuning of the electrical circuit. If you changed the length, it can throw off the entire unit. Obviously, without knowing what you actually did or where you put the unit, it's hard to tell you what's wrong.

Jaguar offered a replacement unit with a longer wiring harness so that it could be mounted off the engine, but you can't just splice in longer wires on the original units. I have the short harness on mine and simply lifted it up out of the valley and mounted it on an aluminum plate between the intake manifolds right behind the AC pump. Not the coolest spot, but better than being bolted to the head down in the valley.

One of our club members, Mike Eck, is working on an upgraded unit to replace the OPUS, using modern components that are less prone to failure. He's also the only one I know who has figured out how to repair these units when they fail. You might want to contact him and get his thoughts. Mikeeckatoptonline.net.

Steve Weinstein
'72 E-type 2+2
'70 XKE FHC