positive power lead

[graham]

Can someone xxplain the route the positive cable from the battery takes to the front of the car and the solenoid switch as cant find any reference in the manual .Its a 73 s130

Graham

[bob_rich]

hi

on my 1973 +2S130 the lead leaves ( or left as it is now stripped down) the battery goes over around the corner of the rear seat back right hand side then down to the floor inside the rear quarter trim and runs along the floor by the passenger side sill going up just past the accelerator pedal through the front bulk head to the starter solenoid. Mine is 4.05 Metres long.

hope this helps

bob

[bob_rich]

hi again

I said passengers side but I may have tried to be too clever and forgot which side of the road you guys drive on!! For passengers side substitute right hand side as defined and anyone sitting normally in the car.

Hope this is clear

regards

Bob

[billwill]

In the two seater the cable is on the left hand side, in the door sill.

[graham]

Thanks for replies- very helpful and as my lead wouldnt be long enough to go via passengers side already decided it had to go drivers side but where I didnt know.

Graham

[pauljones]

Hi guys, sorry to jump on the band waggon but ill soon be changing the loom in my car, (a plus 2 uk car). I had problems with it starting before so i was wondering what size cable to use, do i stick with the origonal or replace it with something a bit bigger, zero gadge possibly.Same question for the earth/return side.

Any help would be usefull

Many thanks,Paul jones

[stugilmour]

Paul, I think the stock cable size is fine. A similar size works OK in my M6 to start a reasonably high compression six cylinder twin cam. My Plus 2 would spin the starter very well prior to tear down; I had starting problems but was related to other issues with the ignition key switch rather that low voltage due to main cable size.

Perhaps prior to tear down check voltage drop from battery positive post to solinoid switch terminal. If excessive, clean terminals thoroughly and re-check.

You mention a ground return; is this another large cable from the battery to the front of the car somewhere? I am plannng in setting up mine this way again; was done this way by mechanic to improve starting. Again, don't think the cable sizes are an issue, but the integrity of the ground connections can be problematic; pay particular attention to rear ground and move to 7/16" right rear tower bolt if not already there. Rear ground to rear trunk floor bobbin does not appear to be very reliable. I think this was the real issue in my car and the added ground return cable is redundant; going to re-install it as it is available and can always disconnect later if it causes ground loop problems.

[pauljones]

Stu,

If i remember rightly the volts at the coil on starting was around 8volts,
It didnt turn over very well even with a full charged battery (and even with a booster pack too).
I was told to fit a bigger main to the solonoid and then to the starter,with the earth return a similar size.
I have a lead running from the battery negative to the chassis at the rear,with a long lead running to the front too.
Perhaps it is this that is causing the problem

Any ideas??? Paul

[stugilmour]

Paul, 8 volts certainly sounds way too low, and would result in hard starting. Question is, what is causing the extreme voltage drop.

I assume 8 volts is during cranking.

Did you measure the 8 volts with a separate meter lead all the way back to the ground battery post? This will assist in determining if the difficulty is on the ground side or power side or both.

Is your ground at the rear to the bolts on the boot floor? If so, they could be suspect as this is a difficult conection to make tight as the bolt threads land in the bobbin in the fibreglass rather than a tapped hole in the frame with better contact to the steel frame. I believe the move to grounding the battery at the 7/16" tapped hole on the right rear tower behind the seat is more reliable.

The ground return cable can't hurt for sure. Where are you terminating it at the front of the car? How is it being connected; the starter has to rely on the engine ground straps for the high current draw, so critical to understand and check the complete ground path from engine block to grounded battery post.

I think the cable sizes are fine, but with only 8 volts at the front of the car, one or more likely several of the connections are dodgey. Replacing the cables will most likely fix things as you will end up cleaning up all the connections during the repair. However, would recommend checking and cleaning every connection first, replacing cable ends if badly corroded or dodgey first, as I expect this will improve things. If you wish to replace the long power cable to be sure of things, it won't hurt to upsize it I suppose, but I don't think it is required and may make shaping the cable to attach to the solinoid a bit more difficult.

Might want to get a helper to take a voltage reading right at the battery during cranking so you know the amount of line loss to the front of the car.

Another suggestion might be to try cranking with the battery connected with jumpers to the solinoid and a firm jumper to the block. This would hopefully rule out the starter motor or solinoid going bad and causing excessive loss. Suppose doesn't matter if you are replacing the cables anyway with the re-wire, but could be another source of problem.

Assuming yours is not a balast resister set-up on the coil, and you are expecting full 12 volts in run and start. Don't have direct experience with balast setup, but understand it should be 12 volts in start and 10 volts in run.


HTH

[pauljones]

Stu,

Thanks for your points.Quite a few to be getting on with.

I think it would be worth mentioning that I have a spyder chassis too.So when I get round to the rebuild that will possibly help matters.
Anyway to answer your points, 8volts was at cranking, raising only to 9 when running. this was measured on the coil,nowhere else.

I think as its a standard setup,the rear ground goes to the bobbin mount you describe and the cable to the front comes from this area to a bolt on the engine mount.

The engine (off memory) doesnt have any cables earthing it to the chassis.Ill check when i get back to it, this sounds like a concern.

Currently, (no joke honestly) i have a coil with out a ballest resistor, however I have an emerald 3d EFI system to put on so that wont be a problem.The concern on this is to get a good electrical suply to all components so i dont fry the brain.

would i be correct in thinking that I have a poor engine earth? and how does that effect power to the coil?

Many thanks,Paul

[bob_rich]

Hi folks

a cable of around 16 square millimetres should be around 0.0011 ohms/metre at around 20C (degrees Centigrade). On a very cold (UK that is around -1C) starter current on my +2 twin cam engine peaked at 250A so a 4 metre lead would drop around 1V. problems with bigger volts drop could be connections, solenoid contacts, and / or earth return through the chassis.

16 square millimetres is around 5AWG. If wanting a bit better then next size is 25 square mm or around 3AWG

hope this helps

Bob

[paddy]

The most important, and unavoidable, voltage drop when cranking comes from the internal resistance of the battery itself. This drop might be 1.5V for a battery in good condition, even when there are no other losses anywhere else in the circuit.

So if, on top of that, you had a 1V loss in the +ve cable then this starts to look a bit marginal. So all other connections do really need to be in tip-top condition to be left with a decent voltage for starting.

Paddy

[leifanten]

On my '69 +2 it runs along the right side of the car.