924Board.org

[Scorpio]

Ive got ALOT of aftermarket electrical units moving into the cabin so i need some good power sources and some good earths.
They include

1)megasquirt
2)megasquirt relay board
3)megajolt light jnr
4) car alarm
5) ride tones
6) remote central locking
7) car amp
8 ) extra cabin lighting
9) dual stage boost controller
10) double din HD GPS/digital TV
10) door popper solenoids

need to ensure i get good power...AMP is getting its own line with inbuilt fuse.

1) Are there any problems with running a high gauge earth cable straight off the battery negative into a distribution block for these appliances? or should i be earthing them just to the body?

2) Are the " H" connections on the relay board sufficient power for everything (except the amp), remembering not everything is running at the same time..From what i remember the "H" connections are a"30" line giving +12V all the time ( not ignition switched) straight off the battery.

p.s the new blue LED's in the new white faced gauges ROCK
_________________
1979 NA
MS1..EFI..
GARRETT T25 TURBO
BILSTEIN SHOCKS
GT BASED CUSTOM BODYKIT

Brisbane , Australia
Think mean think fast
all youll see is
my Porsches Arse!!!

[ideola]

The primary grounding (earth) cable from the battery to the chassis must be sufficiently large to carry the entire electrical load you wish to support in the car. There is a formula based on Ohm's law (I think) for determining appropriate cable sizing based on a variety of factors including amperage, current draw, diameter of cable, conductivity of cable, length of cable, etc. I have a book that explains this, maybe I'll see about digging the details out later.

For now, you want the biggest fattest shortest and least resistant primary ground you can get from the battery to the chassis. This is the foundation.

Then from there, make sure you have at least one, and preferably two, really good grounds from the engine to chassis. Then make sure your starter and alternator have sufficient grounds. Again the formula for wire gauge is based on the parameters above.

My research indicates that welding cable is an excellent alternative for high load grounding material (as well as the primary hot lead from the battery to your starter).

As for individual components, ideally, if you can route their grounds to single distribution unit that would be best (you see the problems we have on our cars with multiple ground points). I've seen some folks create a "ground bus", basically a big cable from front to back with several points at which items throughout the car can be grounded. But if you do a good job to begin with and have sufficient ground to the chassis, going straight to chassis should be fine, as long as you maintain those grounding points (i.e. no rust, good bare metal contact, no frays in the wires, good conductive material, strong clean and shrink-wrapped splices, etc.).

Those are the basics as I understand them, but I'm no electrics whiz, so hopefully some of our electrical gurus can build upon this (or correct me where I'm wrong!).
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erstwhile owner of just about every 924 variant ever made

[Min]

From my understanding of car electrics. Run wires to the engine block for these items. Then run a large welding cable to your battery. Absolutely ensure that your ECU's are grounded to the same place, as well as your wide band oxygen sensor (I'm assuming your going to have one of these?). Its really important that you do that if you want the numbers to make sense between units.

Personally I ran all my goodies directly to the battery, but it looks like a gigantic rats nest. I don't trust chassis grounds for a variety if reasons, the least of which is degrading and changing current paths through your body. So a star grounding method using your engine block is what i would recommend, and what I will be doing on my next squirt installation.

Min
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Custom means it didn't come from a box.
1980 n/a with EDIS and Megasquirt II Injection. 7 different colors and counting.

[Scorpio]

[Min]

[Scorpio]

[Min]