87 Bronco II Grounding Problems Solved

The last year or so I have had problems with the electrical system in my BII, no big surprise, but frustrating. On cold starts the truck would stumble and hesitate and you could make it go if you floored it and stayed on it, but ran rough, especially we you got over 35-40 mph. After much checking of the basics many times, I found all the problems were ground related. The main battery cable runs down towards the block, but stops at the frame where it was clamped to the frame and then continued on to the bolt on the side of the block. Where the bare ground wire was clamped to the frame, the wire was corroded and about half it's normal size. I replaced the clamp on the frame with a bolt and ran two new ground wires, one directly from the battery to the block and then one from the block to the new bolt on the frame. Two of the problems I was having went away.

The next bad ground was the ground from the computer to the body behind the kick panel on the passenger side. The ground appeared to be good with no corrosion, but with the age of the truck the ground path back to the battery had deteriorated. I ran a temporary jumper from the ground bolt by the computer to the battery and took the truck for a drive and miraculously the rest of the driving problems vanished......except for one. I ran a new 16ga wire back to ground point on the front frame by the battery and started working on the last problem.

If you turned on the fan control to medium or high you could see the lights dim and the truck would stumble under load. I took the dash apart and found there is a large ground wire that leaves the fan controller and disappears towards the fuse block, but could not find where it landed but I'm betting it terminated on the firewall sheet metal. I cut the black wire on the fan control and replaced it with a #10ga wire from the controller to the front frame ground point and replaced the spade connectors with a ground lug and re-terminated all the grounds. This solved the fan problem.

Every ground wire I inspected has had some type of corrosion problem, so I am in the process of replacing all of them, one at a time. The Bronco II hasn't run this good since it was new! If you are having any computer related problems that you can't explain......get grounded and see if it solves the problem!
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Good luck!

Thanks for sharing your experience. Great job on tracking down the problems, fixing them, and describing everything. Ground problems are real easy to overlook.

And, welcome to TRS!

there is a ground by the mcu?dang it!

How do you handle the ground from the computer to body ?

Hi all. I'm new to the forum, but recently bought a 1989 Ford Bronco II and am having some issues with it. To be brief the truck runs and it runs pretty good but something seems off. There is some acceleration hesitation especially in low rpms and in first gear and it sometimes seems to stumble or miss even when cruising. I've read a lot of forums and have checked several components and today looked at my negative battery cable and saw that its pretty corroded. My question is could a bad ground to the ECM coming off the negative terminal cause these erratic issues? I think the negative cable needs replaced either way, but I'm wondering if this could solve my issues or if that is a silly thought. Full disclosure I am not a mechanic, but I love to learn and like doing things myself so I don't know a whole lot other than what I've read.

I forgot to mention there is a clicking sound that is pretty audible when the engine is running. I've read a lot about poor oil delivery to the lifters but I don't know that I think that is what it is. I think it may be the injectors opening although it seems pretty dang loud for that, but what it sounds like to me is almost like an electrical sound like an arc. However there are no sparks that can be seen in the dark. Idk if that helps with my prior question but I thought it might. Thanks.

Yanz said:

I forgot to mention there is a clicking sound that is pretty audible when the engine is running. I've read a lot about poor oil delivery to the lifters but I don't know that I think that is what it is. I think it may be the injectors opening although it seems pretty dang loud for that, but what it sounds like to me is almost like an electrical sound like an arc. However there are no sparks that can be seen in the dark. Idk if that helps with my prior question but I thought it might. Thanks.

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My truck has a fast clicking noise too, it ended up being the PCV valve

I would definitely check the connections for your TFI module (attached to the distributor). I had a similar issue where the engine would hesitate at certain rpms, after replacing the TFI. After scratching my head for days as to why putting the new part would cause this problem, I went to change it a 3rd time with a different manufacturer, to discover 2 wires with severe heat fatigue. One of them being the green SPOUT (SPark OUTput) signal wire. The damage was very close to the pin in the connector, so it wasn't found initially, but only upon manipulating the connector many times the wire finally broke lose, leading to the discovery. Apparently that entire system around the TFI module is sensitive to heat, so I would check all the wires/connectors involved in the ignition system!