Changing to negative earth

[Peter Harper]

I have just bought a Pertronix eloctronic ignition kit for my 4A from Moss but it is for negative earth and I am therfore in a situation as my car is posative earth ( USA Import ) do I change the electronic ignition to a posative earth model or switch to negative earth. As all is negative in this day and age there must be a good reason to change.

 

Any feed backs on this cheap electronic ignition system, and apart from the obvious swapping of terminals what else is involved in changing to negative I can live with the ammeter showing discharge when it is charging as I dont fancy changing the terminals behind the dash ( hands too big )

 

Comments please

 

Regards Peter

[jonlar]

Hi Peter, I think the main problem with Positive earth was that it tended to increase corrosion due to more galvanic/electrolytic reaction, also with use of alternators, vehicles had to be Negative earth. If your car is +ve ground, it must be dynamo/generator. It is comparatively easy to change polarity, but you may need to get a battery with poles reversed to current one to keep terminal connectors away from from potential shorts. The dynamo has to be flashed or run as a motor with polarity reversed to get it charging right. With battery leads DISCONNECTED, it is easy enough to remove the 2 knurled securing nuts off the Ammeter bracket and push it out of the dash to reverse connections - don't ever be tempted to fiddle around behind the dash panel wearing metal rings or watch straps etc.. 35 years ago, a mate of mine lost his ring finger to a short from ammeter/battery lead to earth through his wedding ring - arced and welded itself before heating enough to melt and let him get his hand back out.

[Menno van Rij]

Peter - I'm on a Saab 96 forum too. Many Saab owners changed to Pertronix. Most of the time a fit and forget system. But there's one important point to remember: when installed you can not (NEVER!) leave the ignition switched on without running the engine. We all know that leaving the ignition swiched on causes the coil to become hot. It also destroys the Pertronix in no time! That's the reason I didn't change to Pertronix. Some say that a relay of some sort will overcome this problem, but I'm not that good with electronics, so it's not my cup of tea.

 

Menno

[Nigel Lay]

Hello Peter, the correct way to repolarise (I am sure that's how not to spell it) is to remove both wires from the dynamo, reverse the battery so that the -ve terminal goes to earth (chassis/body), you will probably have to swap the battery terminals over as they are different sizes, reconnect the battery and then take a fairly large piece of insulated cable - not like starter motor or anything but not VERY thin bell flex, say like a bit stripped out of a vacuum cleaner flex. Connect one end to the SMALL terminal on the dynamo and then hold the other end on the +ve terminal of the battery for say 5 seconds, no longer. This will change round the residue magnetic field in the dynamo. There is a quicker way but unorthodox that has always worked for me but aparently for some reason not recomended, if you want it please PM me.

Nigel (with TS952)

[BrianC]

There is an excellent step-by-step guide to changing to negative earth by Steve Redway on the TR Register Technicalities CD (Section J2) and originally published in TRaction 135. This also includes reminders to swap connections for ammeter and some added electrical accessories such as fuel pump and fan.