I actually have had zero PMD failures in the 4 years I have had the truck. I had an IP failure, which may not have been a true failure because I had it changed out before I learned more about the truck. The PMD was on the IP and was not the reason for the no-start, the PO never changed the PMD or IP in the many years they had it, and although I did put a new one on a heatsink, its been on the intake for 3 years and I have probed and prodded it plenty. So, although heat cycling is a normal failure, there must be other failure modes electrically related. I kept the PMD off the IP and it still works.
Since Heath's units seem to last pretty long, occasional failures, the success may not be in the solution or location, but simply the consistency in the installation. When you purchase it how does it come, pre-attached? is thermal pad used, or thermal grease, is there a sealant around the PMD, and does the heatsink mount in a chassis grounded manner?
Are those willing to shell out the money for the Heath unit and warranty more likely to have well maintained vehicles with good charging systems and good batteries and the type that doesnt leave the lights on and kill their batteries?
As I recall in one of our calls, Bill said the drivers get milled for flatness, then a mounted to a aluminum alloy not std aluminum something sourced from the aero industry plate.
The driver is epoxied & screwed to the plate with another aero compound that is capable of xferring heat to it. So part of the extra cost in the price is the fabbing required to mill & mount it.
Heath's failures have been few, of the years I've been on the forums I think I can count 1 hand of guys that have had a Heath unit fail he's using the same driver so the risk of it failing is there so I do carry spare with me just in case, but 6 years is a pretty good run so far.
There are some IP mounted drivers from GM that have yet to fail in 200+K even 300K miles, so they can last under hood as several trucks have demonstrated, but population of those is small, next population of fails is underhood intake mounted, and highest survival thus far has been out of engine bay mounted drivers, supported by survey at old site.
IMO multiple fail modes from bad components, improper assembly, cyclic stress of mechanical joints expanding/contracting when combined with heat are what push the ones that have inherent mfg defects or built at tolerance margins in them over top so they are more prone to fail.
One would have to do a 6 sigma project to try drill down to exact fail mode, but since these have been built over such a long period the data used to draw conclusions on is perishable lot A vs B assemebled at X plant with components from X supplier we may never know full root cause of the why.
Voltage deviations very well could also be a variable in the mix, mine have been subjected to dead batteries and crappy gnds on occasion since remoting and none have left me stranded, I've revived dead ones with a retorque of transistor lock nuts to have them fail later, since they are the base of the transitor could be some voltage discrepancies causing premature death of transistor, the chip burried in center between the transitors may give up ghost as well from voltage spikes.
k i am sick of the pmd plague ! every time the better half gets near the damn burban it either runs out of fuel or the pmd dies or both !!!!! that being said i have a 95 puter 6.5 in the trk and a 94 on the stand in the shop,i am going to switch to a non pmd pump i allready know to run a manual switch for the solenoid any advice to make the tranny shift? i dont give a damn about lights in the dash but i need to make the tranny shift normally and not manualon the tree as it is now basically her ride?
or if you problem is more fuel sender related U don't know how much fuel is in tank 
opcorn::bigear:
