Voltage drop????

[MBuhrig]

Hello all,

New here with my 1997 H1 Two-Door.

I have a problem with voltage drop when using indicator light and/or headlights. Any time either head or indicator lights are on my voltage drops to 12v or so causing all my guages to jump. This is even worse when head lights are on, and gauges display wrong oil pressure, temp etc. I replaced one battery which I load tested and found to be bad, however the new battery made no difference and the problem continued. With lights off the volt meter shows about 14-15v. Is this an alternator problem? What should I try next before heading to the local dealer?

Thanks for any input.

[MBuhrig]

Hello all,

New here with my 1997 H1 Two-Door.

I have a problem with voltage drop when using indicator light and/or headlights. Any time either head or indicator lights are on my voltage drops to 12v or so causing all my guages to jump. This is even worse when head lights are on, and gauges display wrong oil pressure, temp etc. I replaced one battery which I load tested and found to be bad, however the new battery made no difference and the problem continued. With lights off the volt meter shows about 14-15v. Is this an alternator problem? What should I try next before heading to the local dealer?

Thanks for any input.

[MBuhrig]

Hello all,

New here with my 1997 H1 Two-Door.

I have a problem with voltage drop when using indicator light and/or headlights. Any time either head or indicator lights are on my voltage drops to 12v or so causing all my guages to jump. This is even worse when head lights are on, and gauges display wrong oil pressure, temp etc. I replaced one battery which I load tested and found to be bad, however the new battery made no difference and the problem continued. With lights off the volt meter shows about 14-15v. Is this an alternator problem? What should I try next before heading to the local dealer?

Thanks for any input.

[Joe]

First, though I don't think this is your issue, the batteries in the Hummer are recommended to always be replaced in pairs from the same lot. It's possible for one new battery to get pulled down by the other if they are not close in spec.

Check your grounds. Also could pull the fuses to try and isolate the source of the problem and then back track from there.

[MBuhrig]

Thanks for the input. I will replace the other battery and then go after the grounds.

I will post the result.

Cheers

[ssgharkness020147]

Which battery did you replace? The "main" battery is the one closest to the windshield, the other battery is the secondary battery. Checking the grounds is a good start, dont forget to clean the connections on the battery too. If that doesnt solve it it could be a bad alternator. A simple way of testing it is to start the truck and touch a wrench or srewdriver to the alternator. The alternator is like a magnet, the wrench or screwdriver should stick on it like they would on a magnet .

[MBuhrig]

I first replace the main (that was the one I found bad under the load test). Today I replaced the other one as well and cleaned and tightened the ground to the starter, battery terminals and 5 (I think) ground points under the dash. Seems to have helped a bit but the gauges still read wrong with the lights on. I will try the magnet test tomorrow.

Also, while wrenching today and getting acquainted with the vehicle I noticed a small leak coming from the break reservoir. There is a small gold cylinder about 1.5 inches in diameter and 3 inches long sticking out horizontally. It looks like a filter. Any input would be appreciated.

Cheers,
Marc

[ssgharkness020147]

Marc,
Could you take a picture of what is leaking and post it? It kind of sounds like your lift pump, with a pic I could tell you what it is for sure and how to fix it.

[MBuhrig]

The alternator checked out fine. I checked out some grounds but still no luck.

I finally took it to took it to the dealer yesterday. They confirmed I do need a new master brake cylinder and I have a ground fault. They said there is a large point at which a lot of grounds come together. The service guy showed me this on the shop manual and said they did not know where it is located! Another certified Hummer mechanic I know said it is behind the driver side wheel well. Can anyone confirm this and I will let the Dealer know. I don't believe they see many H1's there.

Also, are there any good recommendations for All Terrain tires for the 16.5 rim. I have the ply military mud tires now and they ride to rough until they heat up a little.

Thanks again for any input. Hopefully I will get to drive it one day soon.

[belezeebub]

This might help.

One of the first things I do to a car before the winch and stereo and other crap, it to upgrade all the power and ground cables.

I normally run 1 or 0/1 welding cable to the starter and main engine grounds then 2 or 1 gauge from the alt to the battery(s),

Sure its a PITA but I never have ground loops or issues like you are having, and if you own/rent a crimper its normally under 100 bucks and some of your time.

[MBuhrig]

Thanks for the input.

I replaced a few grounds. No luck. The dealer got ahold of it and found a loose engine ground where 4 come together on the back driver's side of the block. I would have never found it!

Seems like the previous owner had some audio equipment installed and they used this ground for some crazy reason....must have had the interior out. All seems to be working out now. Even got to put some miles on her today.

Thanks again.