Electrical Concerns

[BroncoBeth]

I bought an 88 Bronco II a few months back that already had the 4.0 conversion done and a 3" lift. I am learning to work on my own vehicle. I am currently having an electrical problem. At RANDOM I lose all power. So, sometimes it goes out while driving and sometimes it just won't start. And it's no power to anything but the head lights. It's all or nothing. It always starts/restarts within a few minutes but just can't seem to find the problem because it's such an intermittent issue. I have checked the wiring, starter, fuses/relays; all good. I think it may be either the ignition or the PCM. Am I missing anything else? Has anyone else had this problem or can anyone tell me if I'm on the right track. I really hope it's not the PCM, but if it is... What are your thoughts on just grabbing one from a donor at Pick-n-pull or some other junk yard? Please any help, suggestions or info is welcome. I really want to figure this out.

 

[ab_slack]

You say all goes out but the headlights. Do the headlights happen to dim tho? Probably hard to tell.

At least you know what year 4.0L. Do you know if the 4.0L harness stuff was spliced into the B2 wiring or if a full dash swap was done? One of the 4.0L swap tricks is to swap the dash and bring in the harness with the dash. If this was the case it may be easier than if spliced in.

Something as big as your seeing, the one thing I don't recall you mentioning that would be on my list is to check the grounds. You might be losing the main ground to the dash or something like that. I don't know where they all are unfortunately, it is just something I would dig into. That and the main power feeds. Stuff that can affect lots of if a connection is bad.

An intermittent fusible link?

Good luck with it.

 

[JerryC]

I bought an 88 Bronco II a few months back that already had the 4.0 conversion done and a 3" lift. I am learning to work on my own vehicle. I am currently having an electrical problem. At RANDOM I lose all power. So, sometimes it goes out while driving and sometimes it just won't start. And it's no power to anything but the head lights. It's all or nothing. It always starts/restarts within a few minutes but just can't seem to find the problem because it's such an intermittent issue. I have checked the wiring, starter, fuses/relays; all good. I think it may be either the ignition or the PCM. Am I missing anything else? Has anyone else had this problem or can anyone tell me if I'm on the right track. I really hope it's not the PCM, but if it is... What are your thoughts on just grabbing one from a donor at Pick-n-pull or some other junk yard? Please any help, suggestions or info is welcome. I really want to figure this out.

I have no experience with the 4.0 conversion.... But if the head lights work the dash lights should work too as they go through the headlight switch, unless it is bad. HL switches are known to go bad along with plug to the harness.

The ignition switch doesn't control the headlights or dash lights.

I don't remember if the PCM uses the case as a ground or not, but I have this vague memory of reading that rust from water damage between the PCM and body causing problems.

Checking grounds is a good idea, at minimum yours should have battery to frame, frame to engine and engine to firewall ground wires. The engine to firewall is the one most likely to left off after an engine swap or replacement. The factory wire goes from the driver side cylinder head to the firewall. This is where the body gets it's ground. You could just run one straight from the battery.

My last suggestion is to get on ebay and get the electrical manual, it will help you find all the original wiring points.