So I was looking inside my ignition Amp (88 XJS V12), after removing the condenser and testing the new GM module I bought (yes, passed the test).
Am I right that it looks like those two little screws that hold the module in actually ground it to the case, which is then grounded to the intake manifold at the bottom?
I was testing with my ohm meter between the intake manifold and the top of one of those two screws, and sometimes it didn’t register 0 ohms. So I took it apart and gave the case metal a good scraping (where those two screw heads touch), cleaned the two screws, and sanded the connection areas on the intake manifold/bottom of case (where the two bolts hold it down)
You need to ground it.
Terminal “C” on the GM module switches the coil “-” terminal to ground.
The battery voltage to terminal “B” on the module is not switched, it is the power supply for the module.
The attached .pdf file shows the general idea, it does not show any suppression capacitors. This module is good for 12,000RPM on a V12.
Looks like uploaded files and photos do not display automatically for now.
Clicking on the .pdf file worked for me - might not be universal.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
6
OK, so now I’m wondering how many of the problems people have had with these modules has been due to grounding issues. This is especially disconcerting since you’re supposed to install the module with heat sink grease. Does heat sink grease conduct electricity? So if an installer gets carried away with the heat sink grease and slathers it all over the bottom of the module including under the metal contacts surrounding the mounting holes, does that screw up the grounding?
I was thinking the same thing, i had some on the actual screw, but as long as the underside of the head of the grounding screw is not covered, I guess it’s ok. I just saw a tiny bit of corrosion between mine and the metal case. I may pull apart again and test conductivity of that screw, since ground goes from the nut on one end thru screw and to underside of screw head to case.
A digital multimeter will usually show around 0.5ohm even across a dead short.
In this case you are switching around 10A depending on the coil impedance.
Half an ohm is not good, drops coil voltage by 5V.
So use the DMM to get an idea but make sure physically you have a dead short from the module to ground.
Of course you can bolt a wire to the module screw and ground the other end of the wire nearby.
Possibly, yes, with respect to the configuration of the mounting holes.
The module is sold with a GM ‘long’ part number and the short Delco part number. The long number has changed several times over the decades but the Delco number has remained the same.
In the GM system, a part number change typically coincides with a design change or a vendor change. All the latest iterations as supposed to be backwards compatible.
Anyhow, some seem to have one mounting hole with the hex shape and what appears to be a small grounding strap. Others do not. The significance of this has been discussed from time-to-time but I can’t remember where. I’m just two sips into my first cuppa coffee Some Googling would likely reveal more.
Cheers
DD
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
12
Might it be worth adding a ground? Like a wire from that mounting stud to a screw in the side of the case?
Some Googling would likely reveal more.