Electrical Problems / Info

Starter Info
Battery Info

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I Turn the Key but the Engine won't Start and the Starter won't Turn.


My Turn Signal would Light up but Not Flash

The first thing to check is the bulbs. Next check the flasher. If one side works and the other doesn't then the problem isn't the flasher. After that it usually is a bad ground at the light so you have to take the light unit out and check the connections. The last resort is the turn signal switch or a broken wire.

The Door chime Keeps ringing?

The biggest reason for this is that it's wet. The chime is located under the drivers side kick panel, I think near the fuse panel. Usually water leaks in at the corner of the windshield or the hole for the hood release. The chime unit made by Ford.

I left the dome lights on Until the batteries were drained all the way down. Now I can't jump start it.

it sounds like you have a shorted plate in one (or both) of the Hummer's batteries from the deep discharge it underwent. They are both good for nothing other than turning in for a core charge when you buy new batteries now that they have been deep discharged.

You can completely disconnect both batteries, and move the battery from your Jeep to the Hummer to start the truck if you need to. This is a short-term solution as extended starting from one battery will probably damage your jeep's battery. Don't try and use jumper cables as they won't support the current needed to start the Diesel.

Best thing would be to get two replacement batteries and just put them in. Don't put in just one, the batteries should be replaced in sets from the same production lot so they have the same characteristics.

Take the old batteries with you to turn in for a core charge. Your looking for around 1000 Amp cranking, and 800 Cold-Cranking. The batteries are Group 78 and somewhat difficult to find at the 1000/800 level - the more common 800/600 batteries are too small.

The Interstate part number is MTP-78. It comes with an 85 month warranty.

Interior dome and cargo lights

I don't have my interior (dome/ cargo etc) lights working for some reason but when I unlock the doors with the remote control all the lights come on for the duration of the timer. Is there two circuits driving those lights? Is it possible that one fuse can be blown but the remote door lock control of the lights is still functioning? This has me scratching my head.

Replace fuse H5 15amp

I go to crank it and the glow plug cycle is all normal but when I turn the key to start everything electrical dies again.

The batteries are fully charged.

Check your battery cables for tightness and corrosion - clean and re tighten if necessary. The problem as you describe it sounds like a bad connection or high-resistance connection. Using a volt meter to look at voltages on the batteries while this is going on would help greatly too. You might have a bad cell on one of your batteries.

Other things to check:

Check out the fusible link that goes from the batteries to the power distribution block at the base of the windshield - flex it and play with it - see if you have problems from a partial connection.

Check out the power distribution block at the base of the drivers windshield and tighten those nuts too. Watch out for shorting your socket to anything - or even better, do it with the batteries disconnected so you don't have to worry about shorts.

Leaky Window Causes Electrical Problems

I had a speedometer die on me recently, along with my dash lights, and oil gauge (a scary one). Turned out to be a leaky window dripping water on my wire harness causing a grounding bundle to badly corrode. Don't discount the wiring problem. It may be there. If the path to ground is bad the signal of any input will be effected by the changing resistance.

My 95 Won't Go Out of Limp Home Mode

Here is what I have replaced so far in an effort to correct the problem on my 95. The TPS (throttle position sensor), the input speed sensor (transmission), the output speed sensor (transfer case), rebuilt the connector plugs at the ECM, and then both the A and B solenoid in the transmission. The code on the scanner returns a bad B solenoid but replacing it did not fix the problem.

After all of this we replaced the ignition switch. The early hummers had a computer for the transmission, not one for the engine. If your truck is running you theoretically can disconnect the batteries because it is a diesel and doesn't need an electrical spark for ignition it will continue to run. Once you do this you will have lost power to the transmission PCM (power control module). The trans will now go into limp mode.If you disconnect the battery on a running Hummer Diesel engine you will ruin the alternator. It is a characteristic of the alternator.

In other words a possible malfunction in the ignition switch may cause power loss to the trans PCM. A loose switch could lose contact when you hit a bump our just because it's worn.

My Hummer kept jumping into limp mode (stuck in second gear). That is the problem which caused me to bring to two different shops and then the dealer. When I first started to check everything myself, I checked the plug at the trans, the connecter going through the floor near the dog house, and of course changed both solenoids, the input speed sensor, the output speed sensor (on the transfer case tail shaft), and the throttle position sensor. Nothing fixed the problem until AMG told the dealer to check the plug at the firewall. That fixed it. I myself have never seen this plug although I have been all over the vehicle. I even rebuilt the plugs that go into the TCM (harness was unavailable and I knew I could put new plugs on).

AAMCO just replaced all of the solenoids in my tranny for $400.00. I was in limp home mode and feared I needed a whole new tranny.

My Cruise Control is Flaky and or my Speedometer doesn't work.

Check the brake switch at the brake pedal. This switch cancels the cruise and will cause a bunch of problems if it is out of adjustment. The PCM has 2 sources of signal from the brake switch which are exactly opposite each other. One is at 12v and goes to ground when pressed, the other rests at ground and goes to 12v when pressed. I found that the switch needed a slight adjustment. The pcm thought the brake was applied when it wasn't so the cruise control cancelled out.

If you are using LED turn signal and brake lights on your truck you need to install a load resistor under the dash and connect the brake lights to ground or your cruise control and/or high idle switch won't work. There is one switch with 2 connectors on the brake pedal. One is used to remove power to the cruise control (2 wires). The other two wires control the brake lights. One wire on the brake switch goes to power (orange). The other wire goes to the brake lights (red). You attach the wire that goes to the red wire on the brake lights to a 215 ohm resistor to ground. There is an actual AMG 'kit' that comes with a ring lug that is suppose to go under one of the ground lugs on the body pillar. Without the resistor the computer thinks the brakes are on and the cruise or high idle switches will not work.

Another possibility for causing weird problems with your cruise control is stray RF (radio frequencies). 3 years ago I was caravanning from Chicago to Colorado. We were setting our cruise controls so we would be in sync. I'd set my control and use the speedup lever to fine tune my speed. Every so often for no apparent reason the trucks would drift farther apart. After many hours of playing around I realized that each time I keyed my transmitter the cruise returned to the speed where I had originally pressed the set button. It lost the memory of the 'fine tuning'.

If you are running a CB or ham radio in your truck you might check this out.

Read the article on the Output speed sensor

The output speed sensor produces the signal that the cruise control and the speedometer uses. A quick way to test everything up to the speedometer is to try the cruise control. If the cruise control works and your speedometer doesn't then your speedometer is bad. If the cruise doesn't work then check the sender, DRAC and associated wiring .

TT4 and ABS Diagnostics:

Fault Diagnostic Procedure
Faults are stored in the ECU memory in code form. The information can be retrieved by initiating and reading a series of flash and pause sequences (blink codes) on the ABS warning light or with the Wabco Diagnostic Controller. Use of the blink code procedure will determine the location of
the fault prior to performing physical wiring and component tests, thus reducing diagnostic time.
Blink Code Procedure To initiate the blink code procedure, connect the blink code switch jumper Jb-44237 to the Diagnostic Link Connector (DLC) of the vehicle. The jumper allows you to short pin 4 to pin 15 of the DLC.

1. Switch on the ignition, the ABS warning light will illuminate and extinguish if there are no active faults.
2. Five seconds after connecting the switch jumper, the ABS warning light will extinguish, indicating the start of the blink code cycle.
3. The start phase consists of the ABS warning light flashing in the following sequence
b" Pause = 2.5 seconds (long)
b" Flash = 2.5 seconds (long)
b" Pause = 2.5 seconds (long)
b" Flash = 0.5 seconds (short)

4. The first part of the code number A pause of 2.5 seconds precedes a series of short flashes. Count the flashes until the next long pause occurs. The number of short flashes obtained is the first part of the code number.
5. The second part of the code number: A pause of 2.5 seconds occurs between the first and second parts, before a series of short flashes occurs. The number of short flashes forms the second part of the code number.
6. The sequence of the start phase, first and second parts will continue until the switch jumper is deactivated.
NOTE: If you are unsure of the code, do not deactivate the switch jumper from the DLC because the code for that fault will be cleared from the memory.
7. The memory is capable of storing more than one fault. To search the memory, reconnect the switch jumper and await the next start phase.
8. Repeat the procedure until no further faults are stored in the memory. The memory is cleared when a long pause of 7.5 seconds occurs after the start phase.


The battery isn't charging and the voltage is low. http://www.misterfixit.com/alterntr.htm
You may want to check the fusible link that comes off the alternator, I've had a couple of them go.