M998 Instrument cluster and Lights not working

[IResqU2]

So...I am working on a friends M998. He replaced a battery and while doing so shorted it at the terminal to the truck. It didn't want to start so he ordered a PCB. I installed the new one and wired the batteries correctly ( he had it both pos to truck and negatives together). After I changed all of that it runs fine but now the gauges don't work, the stop lights and blinkers don't work and the wait light does not illuminate. I have checked and cleaned the ground behind the dash, it's good. I checked both breakers with an ohm meter and they are fine. 24v coming out of breakers and at all the gauges. What am I missing here???

 

[springer1981]

The ignition switch, in the run position, applies power to only 2 components, the PCB and Circuit Breaker 2 (CB-2). If the truck starts then power is going to the PCB. The PCB also feeds power to CB-1 and that goes to your heater fan switch. My guess is the heater fan works. If this is the case then I doubt you are getting power on the load side of CB-2. Unplug the wires to CB-2 and check for 24v on wire 29B. If you don't have 24v, check the wire back to the run switch. If you do, plug it back into CB-2 and see if you have 24v on the other side of CB-2.

 

[springer1981]

Also, if he had both negatives together, I don't see how that would damage anything. Either it wouldn't flow any power or in the event he actually grounded the 2 negatives and hooked up the positive, it would only be 12v.

 

[IResqU2]

Also, if he had both negatives together, I don't see how that would damage anything. Either it wouldn't flow any power or in the event he actually grounded the 2 negatives and hooked up the positive, it would only be 12v.

When he hooked up the batteries he did hook them backwards which shouldn't do anything but supposedly the PCB could be burnt if the battery was shorted, which he did. I'm not sold that was the problem with all these issues..

 

[IResqU2]

The ignition switch, in the run position, applies power to only 2 components, the PCB and Circuit Breaker 2 (CB-2). If the truck starts then power is going to the PCB. The PCB also feeds power to CB-1 and that goes to your heater fan switch. My guess is the heater fan works. If this is the case then I doubt you are getting power on the load side of CB-2. Unplug the wires to CB-2 and check for 24v on wire 29B. If you don't have 24v, check the wire back to the run switch. If you do, plug it back into CB-2 and see if you have 24v on the other side of CB-2.

I will have to recheck that tomorrow. Pretty sure there is power off CB-2 all the way to the cluster. Is there a ground on the cluster that could be bad making all the instruments not operate? I do get 24v to the 27's and 567 behind the gauges. Also would this cause the brake lights not to work? Im thinking a ground issue somewhere not completing the circuit, bet which one??

 

[springer1981]

When he hooked up the batteries he did hook them backwards which shouldn't do anything but supposedly the PCB could be burnt if the battery was shorted, which he did. I'm not sold that was the problem with all these issues..

Backwards is different than "( he had it both pos to truck and negatives together)". If the batteries were backwards as in Positive to Ground and Negative to Power, that would likely do damage.

 

[springer1981]

I will have to recheck that tomorrow. Pretty sure there is power off CB-2 all the way to the cluster. Is there a ground on the cluster that could be bad making all the instruments not operate? I do get 24v to the 27's and 567 behind the gauges. Also would this cause the brake lights not to work? Im thinking a ground issue somewhere not completing the circuit, bet which one??

Put your hand held volt meter across the volt meter in the dash and see if you have 24v. That is literally ground on 1 side and 27 power on the other. If you have 0v then take your negative volt meter probe and find a ground on the truck, like the case of the PCB. Then see if you have 24v. If you do then it is a ground issue. You can try a jumper wire from a ground on the dash to a body ground and "backfeed" the ground. I would only do this as a test and wouldn't have any lights or anything on. Use a small gauge wire like 18-20ga so it will act like a fuse if there is too much current draw.

 

[papakb]

Part of the circuitry in the PCB is a reverse polarity sensor designed to prevent bad things from happening if you install the batteries backwards.

The instrument cluster diagrams are in the back of the TM 9 2329-280-20-3 manual. Choose any of them since the gauge cluster wiring is basically the same for all models.