Thread: Optima Yellow Top Issues

OK then lets start by ruling the SC80 in or out, as the cause.

If the GREEN LED is on constant, measure the voltage at your cranking battery's positive terminal.

Then measure the voltage at the two studs on the Circuit Breaker, mounted on the side of the SC80.

the voltage should be the same at all three points.

Originally Posted by drivesafe

OK then lets start by ruling the SC80 in or out, as the cause.

If the GREEN LED is on constant, measure the voltage at your cranking battery's positive terminal.

Then measure the voltage at the two studs on the Circuit Breaker, mounted on the side of the SC80.

the voltage should be the same at all three points.

Sorry for the delay but have had some diffuculty getting access to measure as we have just had about 300mm of rain over the last couple of days with 140mm in the last 24hrs

I ducked out quick this morning between downpours and measured the following

Motor off, and has been standing since last Sunday.

Main Batt + stud to earth on car 12.1v, and across both terminals the same 12.1v

Aux Batt + stud to earth now 6.25v and same across both terminals.

SC80 "Yellow" LED is solid.

Now motor on, and it fired first crank with no hesitation.

Main Batt + stud to earth and across both terminals 14.4v

Aux Batt + stud to earth and across both terminals 6.25v

SC80 LED status, solid Yellow, I had it running for about 5 mins before the heavens started to open and I high tailed it back inside.


Oh and guess what, no leaks inside my Defender







May have something to do with the giant silver tarp I've got over it............hahahahahahahahahahahahaha

Hi Glen, are you saying that you had high voltage readings on both the studs on the circuit breaker but a low voltage on the auxiliary battery positive ( + ) terminal to earth was reading just 6.25v?

If this was the case, try placing your multi meter's positive probe on one of the circuit breaker's studs and the negative probe on the auxiliary battery's positive ( + ) terminal.

My guess is that you are going to get another 6.?v reading.

Hi Tim,

No I only read the voltages at the battery terminals, I didn't read your instructions before I grabbed my window of opportunity

I will try and get a measurement at the C/B studs if I get another break in the weather
BTW, this is the SC80 that doesn't have a C/B built in, just the twin tails coming out of the unit, like an SC40 x 2.

I have no idea how old it is as it was already on the car and may have been there for some time, having said that though my SC40 is about 12 yo now and on it's second car and still going strong

When you get a chance, just measure the RED going into the SC80 and the GREY coming out.

If the LED is constant, and the voltages are different, it's the SC80 is the problem and if so, no matter how old it is, it is still under warranty.

If the voltages are the same, the problem is in the cabling between the two batteries, but it does sound like the SC80 is the problem.

Just got another "window" of opportunity, light shower actually so I had a good poke around with a torch through the jumbled spaghetti of wiring and found out that it is actually wired as follows

Red and grey are connected to the + terminal of the main battery and the blue and grey are connected to the + terminal of the aux battery, and the earth/exciter cable to a ground point on the body.


Unfortunately no protection in the form of a C/B or fuse in either

Although the cabling is very messy it is sound with solid connections

I think I'll pull the optima out and see if my charger can save it if I try the recovery mode, as I would prefer not to have to replace the battery and DBS

Hi Glen, if you put the battery charger on your Optima and it does not turn on, get a set of jumper leads and connect your cranking battery to the Optima and then try turning on the charger.

Once the charger starts, disconnect the cranking battery.

Do not start your motor while trying to trick the charger into starting.