Parking Brake Light won't go off

GEM Forum
84

New to forum so forgive me if I should start a new thread.

Purchased 2015 Gem as DOA project. Pervious owner was told the charger was bad and gave up on it. The previous owner had the charger on the floor and a couple of wires disconnected. The 12 system was bad and charger repaired by flight systems but now the hand brake light will not go off and the only relay picking up is on the PSDM. The hand brake has 12 volts from stake on # 6 and the limit switch is working properly. Switched the two control relays around and even changed one for a new one to be sure. All the fuses are okay.

My thoughts are that I have a ground/neutral issue. Cleaned all the chassis ground connections with wire brush but… my charger had both neutrals from the 72 volt and the 12 volt connected to the neutral on the PSDM and no connection to the chassis ground. The diagrams show the 12 volt relay coils connected to chassis ground when in fact I read 12 volts (approx) between chassis ground and neutral so I don’t see any way the the relays are going to pick up. There is a picture in the shop manual which looks like the 12 volt ground is connected to the chassis. I have read in other posts however that the Gem charger is not connected to chassis ground. I am a little gun shy about connecting the 12v to ground because I believe the 12 volt supply is not really fuse protected and easily damaged.

Is the 12 volt supply neutral supposed to be connected to chassis ground or am I missing something?

85

There are technically 2 power systems on this car (3 if you count 120v ACV for the charger).

The main drive battery pack is 72~85v and has a Pos and Neg. Also referred to as B+ and B-.

The Accessory power, 12VDC which drives the car sub systems (headlights, signals, brake lights, horn, wipers, etc) and some monitoring, safety loop stuff. It has a +12v (as you would expect) and like a car, -12v is tied to chassis ground (car frame).

These systems must remain separated. Do not take any of the main battery pack NEG to chassis.

When probing various wires/circuits looking for why something is not working, it is important to know what wire you are working with and use the appropriate reference source. (B- or -12vNeg?)

We might need to establish what you are calling Neutral. That is a common term when working with AC. I think you are referring to -12v or Neg? (but you hop around a lot)

Your statement:

my charger had both neutrals from the 72 volt and the 12 volt connected to the neutral on the PSDM and no connection to the chassis

Is quite alarming and flat out wrong.
Look for and identify the grouped bundle of 4) 12ga wires coming from the charger. The cable sheath ends and the 4 wires splay out in various directions. These wires are Red, Black, Green, and White.

The Red is B+ (+72v) and usually goes to the front of the PSDM stud on the left(driver side), but can be attached in a few less convenient locations.

The Black is B- (-72v) Usually ends up on the front of the PSDM Right side lower stud, but can also be found on top of the controller NEG post.

The Green wire is your Interlock wire and should ONLY go to its’ mate, a slightly different color of green wire. Most people mistake this as a Ground wire and attach it to the frame. ← DON’T DO THIS!!!

The White wire is a Temp Sense wire and it attaches to an Or/Blu wire that runs back to a temp sensor on your battery pack.

You also need to locate the second cable that comes out of your charger. It is usually in a corrugated split loom that goes up to J4 on your PSDM. This is the 12v power source from the DC Converter built in to your DQ Charger. Part way along in this corrugated harness will be a Black wire that breaks out and goes to a screw connection to your chassis.
(see line drawing post 66 of this topic)

Verify that your wires are all going to the correct locations and report back with what you find.

86

Thank you very much for your prompt and very complete explanation.

Yes moving the neutral (-12vdc) wire to chassis ground did solve the problem and everything now works properly.

Thank you also for pointing out that my post was disjointed. Reading it this morning I realize that I should not post when I am under what I call the “IPA” effect that sometimes (never before 5pm) influences my communication skills.