Unusual electrical problems with my 98 Pontiac Transport!! HELP!!! :(?

I had my heater core replaced a couple months ago. Since then all my lights and instrument cluster bezel malfunction. When it gets close to dusk my van makes a weird faint buzzing noise and my turn signal and high beam dash lights light up simultaneously. If I try to use my turn signals they don't work. Also, although the the dash says the high beams are on, they're not. When I do switch to brights, the light goes off. The rear heater/AC control nob on the dash also affects the lights if I turn the knob to any position other than off my headlights turn off completely which isn't normal because if its dark, they are always on whether or not my headlight switch is turned on or off. The heater/AC control nob located in the rear stopped working altogether. The fuse for the AC compressor located under the hood keeps blowing. As soon as we replace it the new fuse instantly blows. We tried replacing the light switch but that didn't help at all. I live in AZ and I have two toddlers with me at all times so it's hard to have to go somewhere with no AC. My husband took most of my dash off already so that we don't get charged "labor costs", but we have no idea where to begin looking for a crossed wire or short. I have a Haynes manual and the original owners manual. Someone please help me understand what's going on so I can go to the repair shop prepared and not get ripped off for something that might be a simple fix.:( I was thinking the "DRL Ambient Light Sensor" could be the culprit??



Thanks in advance for your help!!!Unusual electrical problems with my 98 Pontiac Transport!! HELP!!! :(?
Step no1 if the vehicle has a DRL sensor check it out bec that system does use a relay/timer system and if it has a sensor build into it for detecting if it's getting dark out then this could be part or all of your problem.Note a short in the DRL system could cause the BCM to go haywire causing all weird type of problems.Also note I looked up that vehicle and the only type of ambient sensor listed is the one for the climate control but it also runs to the BCM or a module.

Step no2 have the full dash off and check any wiring harness's that are near by the heater-core and that run along the dash.Someone might have jammed/pinched a harness and it maybe the harness that runs to the BCM and cluster/gauge assembly.

Step no3 check all the grounds bec the dash area should have a few ground wires running to different ground locals, the factory service manual should have charts and charts called the ground local chart and the wiring splice local chart.Check the diagram on the cluster assembly and the headlight switch be sure the grounds have good solid connections, someone might of forget to connect up a ground and comp systems, electronic circuits are sensitive.Note not all ground wires are black they might be a two colour wire one with say a brown and a black stripe etc but your factory book should help you know what colour wires to look for.

Step no4 check and trace these harness wires bec a plug in connection say at the cluster maybe loose or one at the body control module=BCM. Note the BCM is what controls the cluster/dash display gauges etc.Also many times the cluster circuit board inside the assembly has bad soldering connections.The BCM on that may also be involved with the headlight switch or other devices etc that you're having troubles with.

Step no5 trace and test each wire going to and from the BCM and dash and headlight switch be sure none have bad connections.Again your book should tell you what wires and what number of pins the plug in connectors have.

Step no 6 check all the cluster, BCM, dash module diagrams find the 12 volt positive feed wires and pins , plus double check any pins related to the grounds.You then want to check the ignition feed wires it should have a few wires feeding the ignition that are fused supplying it different 12 volt positive ignition feeds.Note any wires that have a higher amp fuse or draw are can have what we call hot spots so check where they run to for obvious hot spots due to extreme heat etc.The ignition then has output wires that may have a fuse in them after the ignition.Each thick wire you see is either for a positive 12 volt feed or the ignition output circuits.Every position of the key ignition switch has wiring like I'am mentioning.Next the ignition and dash etc also has grounds and usually the steering column area has a thick ground wire going to the ignition etc and this harness with that wire can have problems especially if tilt steering.





Hope that helps and best of luck.By the way if you could msg me and send me the schematics of these circuits I'd study them and explain more to you.Note many times ppl pinch or pull or tug on wiring harness's when performing dash work etc so check them closely bec one could be burnt/melted/bare and shorting out.Lastly the comp system may have a error code/codes stored even if the engine light isn't on and many shops or part stores will do the scan for free or you can purchase a basic scanner for it for as little as 20 bucks.