Cooling Fan Problem

Apologize if this is not the correct forum as I could not see one for this thread. If not please move.

Vehicle: 2003 Ford Ranger 3.0L manual trans. 88k miles

I have just installed an electric cooling fan to replace the factory clutch fan because I am trying to get the engine to heat faster after start and run hotter (closer to 195 stat setting). The fan has improved both of those.

The fan is aftermarket TYC 621860 for 2008-10 Chrysler Town & County 3.3L. The fan fits perfectly inside my factory shroud. Fan draws 45 amp start and 18 amp full speed run.

I am using a Flex-a-lite controller 31163 which starts with 60% for cooling and 60% for AC but will ramp up if heat calls for more rpm. The controller uses PWM to achieve variable speed. Controller wired directly to good battery. The stock alternator is a 95 amp.

Fan is working great, except on fan start. At idle, not moving, my speedo will bounce from zero to 5-10 mph, then settle when fan is spinning. No bouncing when moving or when fan turns off. I found out that turning the headlights on eliminated the bounce. I had the alternator checked by professional alternator shop who found no voltage surges or other problem with the alternator. I was going to replace the voltage regulator anyway to see if that helped. On removing the old voltage regulator I found the alternator slip rings badly worn and grooved for a vehicle with 88k. I replaced the alternator with a new 130 amp made for this truck.

After installation of new alternator the bouncing speedo was still there. Also with the new alternator turning the headlights on does not stop the bouncing.

Speedo uses a VSS to the PCM to show speed.

I'm assuming some EMI/EMF from the fan motor is causing this??? I have researched about some possible solves, which included a capacitor across the plus/minus wires as close to the the fan as possible to reduce the electrical interference. Flex-a-lite has never seen this before, but have seen somewhat same for the tachometer. No solve from them so far.

Looking for help on the cause and how to solve this. It's not a problem for me unless this affects my PCM somehow.

Thanks,
Peter

Update:

This weekend I thought I'd make sure all my engine and body grounds were good. There is a large ground strap that runs from the engine block to the firewall. I removed and cleaned both ends. The engine connection had some corrosion/dirt on it and I cleaned, wire brushed and sanded both connection points. Today driving the truck with AC on the speedo bounce was considerably less, barely moving the needle, and only on the last part of the 60% speed, not right at the start.

I'll look for more ground points and clean them.