I've been working on my moms 98 Blazer LT for the past few years on and off. The problem started a few years ago when the car began to stall ,have trouble starting then just stopped altogether.. While looking about the engine bay I noticed the coil and map sensor plugs were slightly burnt (not by a short but resembled a small isolated engine fire), There were a few scorched wires but none exposed, In any event I decided to replace the harness. I managed to find an excellent replacement on eBay (same year) and installed it without any problems, that is except for the oil sensor plug next to the distributor. The old one has a 3 prong plug but the replacement has 1 (is there more than 1 type of harness for a 98 blazer 4.3 engine?) Now after the replacement my problem (or should I say the cars) is all the chassis electrical is weak. It has dim lights all around, starter wont engage, horn sounds like a sick moose but, interestingly the DRL relay buzzes and the A/C clutch engages and disengages. After all the red flag warnings I quickly disconnected the battery (which was fully charged with 12.4 volts) Both pos and neg batt cables were replaced with Delco replacements and virtually all sensors 2 years ago. Now I don't know if this is related but before its demise on both the drivers side, the radio speakers (dash and doors) no longer worked and the master power windows/locks /mirror switch stayed illuminated day or night with engine on or off which drains the batt. Any ideas out there?

 

What is the resting battery voltage at the battery terminals before you start. What is the voltage when you turn the truck on and all this wonky behavior starts?

Do you have an amp clamp meter?

George

 

Fortunately I do have a volt meter,
Here are the battery stages,
The battery alone is at 12.43 volts (not hooked up)
When hooked up 10.75v and dropping volts
When ignition turned on (not running) 9.75v
Note, The A/C clutch engages (interior climate control switch is off) and DRL relay buzzes

 

You have either:

1. A bad battery, those voltage readings are too low at hook up. A fully charged battery BTW hold 12.6V open circuit (no load).
2. You have some marginal connections, corrosion, frayed wires, partially blown fusible links near the battery.
3. Something drawing mad amperage, like 50+ amps (bad starter, shorted alternator diodes, etc. That why I asked if you have an amp clamp meter to see how much current draw you have.

If your not flush with tools the best bet to start maybe a battery load test at a parts store. They draw 100 amps from the battery and see how much voltage drop you get. We cant go any further until we know we have a good battery and then we can test some key voltage drops or current draw.

George